Topic outline

  • UNIT 1 SOUND WAVES


    Key unit competence: Analyze the effects of sound waves in elastic medium
    My goals
    • Describe how sound propagates through a substance
    • Give the characteristics of sound.
    • Relate loudness and pitch to amplitude and frequency
    • Carry out calculations relating decibels and intensity
    • Establish relationship between characteristics of notes and sound
    waves
    • Explain beats and establish beat frequency
    • Explain Doppler – Fizeau effect.
    • Give examples of musical pipe instruments.
    • Explain Doppler – Fizeau effect.
    • Give examples of musical pipe instruments.
    • Establish the fundamental frequency and 2nd harmonic, 3rd harmonic,
    in vibrating strings and in pipes
    INTRODUCTORY ACTIVITY
    1. Most people like to listen to music, but hardly anyone likes to listen to
    noise. What is the difference between a musical sound and noise?
    2. A guitarist plays any note. The sound is made by the vibration of the
    guitar string and propagates as a wave through the air and reaches your
    ear. Which of the following statement is the right?
    • The vibration on the string and the vibration in the air have the
    same wavelength.
    • They have the same frequency.
    • They have the same speed.
    • None of the above is the same in the air as it is on the string.
    Questions
    a. Explain the meaning of underlined terms used in the text above
    b. Do you think, it was 100% correct for Claudette to relate sound waves to
    light waves. Explain.
    c. There is somewhere where she was asked to discuss the different media
    in which sound waves can travel. Discuss these different media and talk
    about velocity of sound waves in the stated media.
    d. In one of the paragraph, Claudette said that the laws governing reflection
    and refraction of sound waves were similar to those of light. Can you
    explain these laws (Use diagrams where possible)
    e. Assuming that you were an interviewer and the interview was out of
    80.What mark would you award Claudette? Why?
    1.1. CHARACTERISTICS AND PROPERTIES OF SOUND WAVES
    ACTIVITY 1.1: Properties of sound
    Read the scenario below and answer the questions that follow.
    On an interview for Physics placement in a certain school in Rwanda,
    Claudette a S.6 leaver who had applied for the job was asked about
    sound waves during the interview. She was asked to state the properties
    of sound waves. Confidently, she responded that the properties are
    reflection, refraction, diffraction and interference. This was enough
    to make Claudette pass the first level of the interview.
    However, in the second step, she was required to discuss different media
    in which sound waves can propagate. Claudette started discussing
    these different media. What surprised the interviewer was Claudette’s
    ability to relate sound waves to other kinds of waves stating that these
    waves behaves the same way when they pass from one medium to

    another.

    Looking at Claudette’s face, the interviewer asked her to discuss the laws
    governing reflection and refraction of sound waves. With a smile, she
    started by saying that since sound waves have the same properties as for
    light; these laws therefore do not change.
    As she was attempting to state them, the interviewer stopped her and
    congratulated her upon her confidence and bravery she showed in the room.
    She was directly told that she was successful and she was given the job.
    Claudette is now working as assistant S2 Physics teacher and doubles as a
    Physics laboratory attendant.
    1.1.1 Properties of sound waves
    Most of us start our lives by producing sound waves! We spend much of our
    life surrounded by objects which produce sound waves. Most machines in
    use vibrate and produce sound so the only sure way to silence them would
    be to put them in vacuum where there would be no surrounding medium for
    the vibrating surfaces of the machine to push against, hence no sound waves.
    Some physiologists are concerned with how speech is produced, how speech
    impairment might be corrected, how hearing loss can be alleviated.
    Sound is associated with our sense of hearing and, therefore, with the physiology
    of our ears that intercept the sound and the psychology of our brain which
    interprets the sensations that reach our ears. Sound waves are longitudinal
    mechanical waves that can travel through solids, liquids, or gases.
    As the sound wave propagates, many interactions can occur, including reflection,
    refraction, diffraction and interference. When a sound wave hits a surface, a
    part of the energy gets scattered while a part of it is absorbed. Absorption is
    the phenomenon of the wave where the energy of sound wave gets transformed
    from one form to another. The high frequency sound waves are more easily
    absorbed than low frequency sounds. It happens most with the soft materials.
    1.1.2 Characteristics of sound waves
    ACTIVITY 1.2: Characteristics of sound waves
    1. How to calculate the speed of sound waves in different materials.
    2. How to calculate the intensity of a sound wave.
    3. From the Fig.1.2, can you hear the ultrasound waves that a bat uses

    for echolocation? Why or why not?

    Fig.1. 2: Range of frequencies heard by various animals and human (Randall & Knight.,-

    Physics for scientists and engineers: Stategic approach., 2008)

    Usually, the characteristics used to describe waves are period, frequency,
    wavelength, and amplitude.
    a. Frequency ranges
    Any periodic motion has a frequency, which is the number of complete cycles
    in a second and a period which is the time used to complete one cycle. While
    the frequency is measured in Hertz (Hz), the period is measured in seconds (s).
    For a wave, the frequency is the number of wave cycles that pass a point in a
    second. A wave’s frequency equals the frequency of the vibrating source
    producing the wave.
    Sound waves are classified into three categories that cover different frequency
    ranges:
    • Audible soundlies within the range of sensitivity of the human ear.
    They can be generated in a variety of ways, such as musical instruments,
    human voices, or loudspeakers. It is almost impossible to hear sounds
    outside the range of 20 Hz to 20 kHz. These are the limits of audibility
    for human beings but the range decreases with age.
    • Infrasonic waveshave frequencies below the audible range. They are
    sound waves with frequencies that are below 20 Hz limit. Some animals
    such as elephants can use infrasonic waves to communicate with each
    other, even when they are separated by many kilometers. Rhinoceros
    also use infrasonic as low as 5 Hz to call one another.
    • Ultrasonic waves have frequencies above the audible range. They
    are sound waves whose frequencies are higher than 20 KHz. You may
    have used a “silent” whistle to retrieve your dog. The ultrasonic sound
    emitted by that device is easily heard by dogs, although humans cannot
    detect it at all. Ultrasonic waves are also used in medical imaging.
    Many animals hear a much wider range of frequencies than human beings do.
    For example, dog whistles vibrate at a higher frequency than the human ear
    can detect, while evidence suggests that dolphins and whales communicate at
    frequencies beyond human hearing (ultrasound) (Cutnell & Johnson, 2006).
    b. Wavelength
    Wavelength is the distance covered by a wave in a period. It is represented by
    the separation between a point on one wave and a similar point on the next
    cycle of the wave. For a transverse wave, wavelength is measured between
    adjacent crests or between adjacent troughs. For a longitudinal wave such as
    sound wave, wavelength is the distance between adjacent compressions or
    rarefaction.
    c. Speed of sound
    For a periodic wave, the shape of the string at any instant is a repeating pattern.
    The length of one complete wave pattern is the distance from one crest to the
    next or from one trough to the next or from any point to the corresponding point
    on the next repetition of the wave shape. We call this distance the wavelength
    of the wave, denoted by the Greek letter lambda (λ).
    The wave pattern travels with constant speed and advances a distance of one
    wavelength in a time interval of one period T. So the wave speed is given by

    where f is the frequency of the wave.
    Sound travels faster in liquids and solids than in gases, since the particles in
    liquids and solids are closer together and can respond more quickly to the
    motion of their neighbors. As examples, the speed of sound is 331 m/s in
    air,1500 m/s in water and 5000 m/s in iron (though these can change depending

    on temperature and pressure). Sound does not travel in vacuum.

    Example 1.1: Wavelength of musical sound
    Example 1.1 Wavelength of a musical sound
    1) Sound waves can propagate in air. The speed of the sound depends
    on temperature of the air; at 200 C it is 344 m/ s it is. What is the
    wavelength of a sound wave in air if the frequency is 262 Hz (the
    approximate frequency of middle C on a piano)?

    Answer:

    Using Equation of wave (1.01): 

    Factors which affect the velocity of sound in air
    • The speed of sound waves in a medium depends on the compressibility
    and density of the medium. If the medium is a liquid or a gas and has a
    bulk modulus Band density ρ , the speed of sound waves in that medium

    is given by:                 (1.02)

    • It is interesting to compare this expression with the equation

    applicable to transverse waves on a string. In both cases,

    the wave speed depends on an elastic property of the medium (bulk
    modulus B or tension in the string T) and on an inertial property of the
    medium (the density ρ or linear mass μ ).
    In fact, the speed of all mechanical waves follows an expression of the

    general form                      (1.03)

    • For longitudinal sound waves in a solid rod of material, for example,
    the speed of sound depends on Young’s modulus Y and the density ρ

    Changes of pressure have no effect on the velocity of sound in air.

    Sir Isaac Newton showed that:                                          (1.04)

    • In accordance with Boyle’s law, if the pressure of a fixed mass of air is
    doubled, the volume will be halved. Hence the density will be doubled.
    Thus at constant temperature, the ratio P⁄ρ
    will always remain constant
    no matter how the pressure may change. The speed of sound increases
    with temperature . If the air temperature increases at constant pressure
    the air will expand according to Charles’ law, and therefore become
    less dense. The ratio P⁄ρ
    will therefore increase, and hence the speed of
    sound increases with temperature. For sound traveling through air, the

    relationship between wave speed and medium temperature is            ( 1 . 0 5 )

    Where v0 331m/ s  = is the speed of sound in air(at 0 degree Celsius
    and normal pressure) .
    • The speed of sound in air at standard temperature and pressure (25
    oC, 760 mm of mercury) is 343 m/s. It is determined by how often the
    air molecules collide. The speed of sound increases by about 6 m/s if

    the temperature increases by 10 oC (Glencoe, 2005).

    d.Amplitude
    The amplitude of a wave is the maximum displacement of the medium from its
    rest position. The amplitude of a transverse wave is the distance from the rest
    position to a crest or a trough. The more energy a wave has, the greater is its
    amplitude.
    1.1.3 Checking my progress
    1. The correct statement about sound waves is that:
    a. They are transverse waves
    b. They can be polarized
    c. They require material medium to propagate
    2. Sound travels in
    a. Air b. Wate c. Iron d. All of these
    3. Two men talk on the moon. Assuming that the thin layer of gases on the
    moon is negligible, which of the following is the right answer:
    a. They hear each other with lower frequency
    b. They hear each other with higher frequency
    c. They can hear each other at such frequency
    d. They cannot hear each other at all
    4. Do you expect an echo to return to you more quickly on a hot day or a
    cold day?
    a. Hot day. b. Cold day. c. Same on both days.
    5. A sound wave is different than a light wave in that a sound wave is:
    a. Produced by an oscillating object and a light wave is not.
    b. Not capable of traveling through a vacuum.
    c. Not capable of diffracting and a light wave is.
    d. Capable of existing with a variety of frequencies and a light wave
    has a single frequency.
    6. A spider of mass 0.30 g waits in its web of negligible mass see Fig. below.
    A slight movement causes the web to vibrate with a frequency of about
    15 Hz.

    Fig.1. 3 A spider of mass waits in its web

    a. Estimate the value of the spring stiffness constant k for the web
    assuming simple harmonic motion.
    b. At what frequency would you expect the web to vibrate if an insect

    of mass 0.10 g were trapped in addition to the spider?

    1.2 PRODUCTION OF STATIONARY SOUND WAVES

    ACTIVITY 1.3: Production of stationary sound waves


    Fig.1. 4: A guitarist.

    Look at the Fig.1.4 of guitarist and then answer the following question.
    1. How do vibrations cause sound?
    2. What determines the particular frequencies of sound produced by
    an organ or a flute?
    3. How resonance occurs in musical instruments?
    4. How to describe what happens when two sound waves of slightly

    different frequencies are combined?

    1.2.1 Sound in pipes
    The source of any sound is vibrating object. Almost any object can vibrate
    and hence be a source of sound. For musical instruments, the source is set
    into vibration by striking, plucking, bowing, or blowing. Standing waves (also
    known as stationary waves are superposition of two waves moving in opposite
    directions, each having the same amplitude and frequency) are produced and
    the source vibrates at its natural resonant frequencies.
    The most widely used instruments that produce sound waves make use of
    vibrating strings, such as the violin, guitar, and piano or make use of vibrating
    columns of air, such as the flute, trumpet, and pipe organ. They are called wind
    instruments.
    We can create a standing wave:
    • In a tube, which is open on both ends. The open end of a tube is
    approximately a node in the pressure (or an antinode in the longitudinal
    displacement).
    • In a tube, which is open on one end and closed on the other end. The
    closed end of a tube is an antinode in the pressure (or a node in the
    longitudinal displacement).
    In both cases a pressure node is always a displacement antinode and vice versa.
    a. Tube of length L with two open ends
    An open pipe is one which is open at both ends. The length of the pipe is the

    distancebetween consecutive antinodes. But the distance between consecutive

    antinode is               (1.06)

    The longest standing wave in a tube of length L with two open ends has
    displacement antinodes (pressure nodes) at both ends. It is called the

    fundamental.


    Notes with higher frequencies than fundamental can be obtained from the pipe
    by blowing harder. The stationary wave in the open pipe has always an antinode

    at each end. 

    The next longest standing wave in a tube of length L with two open ends is the
    second harmonic (first overtone). It also has displacement antinodes at each

    end.


    Fig.1. 6: First overtone (second harmonic).

    The second overtone is obtained from Fig. 1.6 and is the third harmonic.

    Fig.1. 7: Second overtone (third harmonic).

    An integer number of half wavelength has to fit into the tube of length L:

                 (1.07)

    For a tube with two open ends, all frequencies  fn− 1  =nf0  with n equal to an
    integer are natural frequencies.
    The frequency f of fundamental note emitted by a vibrating string of length L,

    mass per unit length m and under tension T is given by           (1.08)

    Example 1.3
    The fundamental frequency of a pipe that is open at both ends is 594 Hz.
    a. How long is this pipe?
    b. Find the wavelength. Assume the temperature is 20oc
    c. Determine the fundamental frequency of the flute when all holes are
    covered and the temperature is 10 °C instead of 20 °C?

    Answer :

    Quick check 1.1: Standing sound waves are produced in a pipe that is 1.20
    m long. For the fundamental and first two overtones, determine the locations
    along the pipe (measured from the left end) of the displacement nodes and
    the pressure nodes if the pipe is open at both ends.
    b. Tube of length L with one open end and one closed end.
    The longest standing wave in a tube of length L with one open end and one
    closed end has a displacement antinode at the open end and a displacement
    node at the closed end.

    This is the fundamental.        (1.09)


    Fig.1. 8: Fundamental note (1st harmonic).

    The next longest standing wave in a tube of length in a tube of length L with one
    open end and one closed end is the third harmonic (second overtone). It also

    has a displacement antinode at one end and a node at the other.

                     (1.10)

    Fig.1. 9: First overtone (third harmonic)

    The next longest standing wave in a tube of length L with one open end and one

    closed end is the second overtone (fifth harmonic).

                  (1.11)

    Fig.1. 10: Second overtone (fifth harmonic)

    An odd-integer number of quarter wavelength has to fit into the tube of length L.

    For a tube with one open end and one closed end, frequencies  

    with n equal to an odd integer are natural frequencies.
    Only odd harmonics of the fundamental are natural frequencies.
    Another way to analyze the vibrations in a uniform tube is to consider
    a description in terms of the pressure in the air. Where the air in a wave
    is compressed, the pressure is higher, whereas in a wave expansion (or
    rarefaction), the pressure is less than normal. We call a region of increased
    density a compression; a region of reduced density is a rarefaction.
    The wavelength is the distance from one compression to the next or from one

    rarefaction to the next.


    Fig.1. 11: Pressure variation in the air: Graphs of the three simplest modes of vibration (standing

    waves) for a uniform tube open at both ends (“open tube”).

    The open end of a tube is open to the atmosphere. Hence the pressure variation
    at an open end must be a node: the pressure does not alternate, but remains at

    the outside atmospheric pressure as shown in Fig.1.12.


    Fig.1. 12: Modes of vibration (standing waves) for a tube closed at one end (“closed tube”).

    If a tube has a closed end, the pressure at that closed end can readily alternate
    to be above or below atmospheric pressure. Hence there is a pressure antinode
    at a closed end of a tube. There can be pressure nodes and antinodes within the
    tube as shown in Fig.1.12.

    Example 1.4

    1. A section of drainage culvert 1.23 m in length makes a howling noise
    when the wind blows.
    a. Determine the frequencies of the first three harmonics of the
    culvert if it is open at both ends. Take v = 343 m/s as the speed
    of sound in air.
    b. What are the three lowest natural frequencies of the culvert if
    it is blocked at one end?
    c. For the culvert open at both ends, how many of the harmonics
    present fall within the normal human hearing range (20 Hz to
    17 000 Hz)?
    Answer
    a. The frequency of the first harmonic of a pipe open at both
    ends is Because both ends are open, all harmonics are present;

    thus,

    Quick check 1.2:
    Standing sound waves are produced in a pipe that is 1.20 m long. For the
    fundamental and first two overtones, determine the locations along the pipe
    (measured from the left end) of the displacement nodes and the pressure
    nodes if the pipe is closed at the left end and open at the right end.
    1.2.2 Vibrating strings
    The string is a tightly stretched wire or length of gut. When it is struck, bowed
    or plucked, progressive transverse waves travel to both ends, which are fixed,
    where they are reflected to meet the incident waves. A stationary wave pattern
    is formed for waves whose wavelengths fit into the length of the string, i.e.
    resonance occurs.
    If you shake one end of a cord (slinky) and the other end is kept fixed, a
    inverted. The frequencies at which standing waves are produced are the natural
    frequencies or resonant frequencies of the cord. A progressive sound wave (i.e.
    a longitudinal wave) is produced in the surrounding air with frequency equal
    to that of the stationary transverse wave on the string.
    Now let consider a cord stretched between two supports that is plucked like
    a guitar or violin string. Waves of a great variety of frequencies will travel in
    both directions along the string, will be reflected at the ends, and will be travel
    back in the opposite direction. The ends of the string, since they are fixed, will
    be nodes.
    The lowest frequency, called the fundamental frequency, corresponds to one
    antinode (or loop) and corresponds to whole length of the string i.e, L= λ⁄2the
    other natural frequencies are called overtones or harmonics. The next mode
    after the fundamental has two loops and is called the second harmonic or first
    overtone and so on.
    Fundamental note (first harmonic):       (1.13)
    The frequency:                      (1.14)

    It was stated that the speed of a transverse wave travelling along a string is

    given by 

    The frequency of the vibration is given by:              (1.15)

    First overtone (second harmonic) of a string plucked in the middle corresponds
    to a stationary wave which has nodes at the fixed ends and antinode in the
    middle. If is λ1
    the wave length it can be seen that:
                          (1.16)
    The frequency of fist overtone is given by: 
    In order to find the frequency f of each vibration we use equation: 
    and we see that                 (1.17)
    where               (1.18)
    Consider a string of length L fixed at both ends, as shown in Fig.1.12. Standing
    waves are set up in the string by a continuous superposition of wave incident
    on and reflected from the ends.
    Note that there is a boundary condition for the waves on the string. The ends of
    the string, because they are fixed, must necessarily have zero displacement and

    are, therefore, nodes by definition.

    Fig.1. 13: Fundamental and first two overtones: (a) A string of length L fixed at

    both ends.

    The normal modes of vibration form a harmonic series: (b) the fundamental
    note (first harmonic); (c) First overtone (second harmonic); (d) the second

    overtone (third harmonic) (Halliday, Resneck, & Walker, 2007).

    Quick check 1.3:
    Middle C on a piano has a fundamental frequency of 262 Hz, and the first A
    above middle C has a fundamental frequency of 440 Hz.
    a. Calculate the frequencies of the next two harmonics of the C string.
    b. If the A and C strings have the same linear mass densityμ and
    length L, determine the ratio of tensions in the two strings.
    c. With respect to a real piano, the assumption we made in (b) is only
    partially true. The string densities are equal, but the length of the A
    string is only 64 % of the length of the C string. What is the ratio of
    their tensions?
    1.2.3. Wave Interference and Superposition
    a. Wave interference
    Up to this point we’ve been discussing waves that propagate continuously in
    the same direction. But when a wave strikes the boundaries of its medium, all
    or part of the wave is reflected.
    When you yell at a building wall or a cliff face some distance away, the sound
    wave is reflected from the rigid surface and you hear an echo. When you flip the
    end of a rope whose far end is tied to a rigid support, a pulse travels the length
    of the rope and is reflected back to you. In both cases, the initial and reflected
    waves overlap in the same region of the medium. This overlapping of waves is
    called interference.
    In general, the term “interference” refers to what happens when two or more
    waves pass through the same region at the same time Fig.1.14 shows an example

    of another type of interference that involves waves that spread out in space.

    Fig.1. 14: Two speakers driven by the same amplifier: Constructive interference occurs at point P

    and destructive interference occurs at Q.

    Two speakers, driven in phase by the same amplifier, emit identical sinusoidal
    sound waves with the same constant frequency. We place a microphone at
    point P in the figure, equidistant from the speakers. Wave crests emitted from
    the two speakers at the same time travel equal distances and arrive at point
    P at the same time; hence the waves arrive in phase, and there is constructive
    interference.
    The total wave amplitude at P is twice the amplitude from each individual wave,
    and we can measure this combined amplitude with the microphone.
    Now let’s move the microphone to point Q, where the distances from the
    two speakers to the microphone differ by a half-wavelength. Then the two
    waves arrive a half-cycle out of step, or out of phase; a positive crest from one
    speaker arrives at the same time as a negative crest from the other. Destructive
    interference takes place, and the amplitude measured by the microphone is
    much smaller than when only one speaker is present. If the amplitudes from
    the two speakers are equal, the two waves cancel each other out completely at
    point Q, and the total amplitude there is zero.
    b. The principle of superposition
    Combining the displacements of the separate pulses at each point to obtain
    the actual displacement is an example of the principle of superposition: “When
    two waves overlap, the actual displacement of any point on the string at any
    time is obtained by adding the displacement the point would have if only the
    first wave were present and the displacement it would have if only the second
    wave were present”.
    In other words, the wave function y(t, x) that describes the resulting motion in
    this situation is obtained by adding the two wave functions for the two separate

    waves:        (1.19)


    As we saw with transverse waves, when two waves meet they create a third
    wave that is a combination of the other two waves. This third wave is actually
    the sum of the two waves at the points where they meet. The two original
    waves are still there and will continue along their paths after passing through
    each other. After passing the third wave no longer exists. Its amplitude has the

    magnitude                    (1.21)

    ACTIVITY 1.4:
    Problem 1
    The Adventures of Marvin the Mouse: You and your friend are walking
    down by the pool when you hear a cry for help. Poor Marvin the Mouse
    has fallen into the pool and needs your help. The sides of the pool are
    to slippery for Marvin to climb out but there is an inner tube anchored
    in the center of the pool. Oh no! The sides of the inner tube are too
    slippery and high for Marvin to climb. He’s getting tired and can’t swim
    to the sides; he has just enough energy to float by the inner tube. Having
    studied about waves, you and your friend take up positions on opposite
    sides of the pool. How did you help Marvin get safely onto the inner
    tube?
    Problem 2: Dance club designer
    You are the designer of a new Dance Club. You have been informed that
    you need to design the club in such a way that the telephone is placed
    in a location that allows the customers to hear the people on the other
    side. The phone company states that they can only put the phone line
    in at a point 20 m from the stage. Develop a model which allows the
    customers to use the phone with the least amount of trouble given that
    the phone must be placed at a distance of 20 m, (2/3 the room size),
    from the stage. This will be an area where there will be virtually no
    sound.
    c. Resonance of sound
    We have seen that a system such as a taut string is capable of oscillating in one
    or more normal modes of oscillation. If a periodic force is applied to such a
    system, the amplitude of the resulting motion is greater than normal when the
    frequency of the applied force is equal to or nearly equal to one of the natural
    frequencies of the system. This phenomenon is known as resonance. Although
    a block–spring system or a simple pendulum has only one natural frequency,
    standing-wave systems can have a whole set of natural frequencies.
    Because oscillating systems exhibits large amplitude when driven at any of
    its natural frequencies, these frequencies are often referred to as resonance
    frequencies. Fig.1.15 shows the response of an oscillating system to various
    driving frequencies, where one of the resonance frequencies of the system is

    denoted by f0


    Fig.1. 15: Graph of the amplitude versus driving frequency for oscillating system. The amplitude
    is a maximum at the resonance frequency. Note that the curve is not symmetric (Halliday, Resneck,

    & Walker, 2007)

    One of our best models of resonance in a musical instrument is a resonance
    tube. This is a hollow cylindrical tube partially filled with water and forced into
    vibration by a tuning fork (Fig.1.16). The tuning fork is the object that forced
    the air, inside the resonance tube, into resonance.

    Fig.1. 16: Turning fork forcing air column into resonance
    As the tines of the tuning fork vibrate at their own natural frequency, they
    created sound waves that impinge upon the opening of the resonance tube.
    These impinging sound waves produced by the tuning fork force air inside
    of the resonance tube to vibrate at the same frequency. Yet, in the absence of
    resonance, the sound of these vibrations is not loud enough to discern.
    Resonance only occurs when the first object is vibrating at the natural frequency
    of the second object. So if the frequency at which the tuning fork vibrates is not
    identical to one of the natural frequencies of the air column inside the resonance
    tube, resonance will not occur and the two objects will not sound out together
    with a loud sound. But the location of the water level can be altered by raising
    and lowering a reservoir of water, thus decreasing or increasing the length of
    the air column.
    So by raising and lowering the water level, the natural frequency of the air in
    the tube could be matched to the frequency at which the tuning fork vibrates.
    When the match is achieved, the tuning fork forces the air column inside of
    the resonance tube to vibrate at its own natural frequency and resonance is
    achieved. The result of resonance is always a big vibration - that is, a loud sound.
    A more spectacular example is a singer breaking a wine glass with her amplified
    voice. A good-quality wine glass has normal-mode frequencies that you can
    hear by tapping it.
    If the singer emits a loud note with a frequency corresponding exactly to one of
    these normal-mode frequencies, large-amplitude oscillations can build up and
    break the glass (Fig. 1.17)

    Fig.1. 17: Some singers can shatter a wine glass by maintaining a certain frequency of their voice
    for seconds, (a) Standing-wave pattern in a vibrating wine glass. (b) A wine glass shattered by the

    amplified sound of a human voice

    d. Beats and its phenomena
    Beats occur when two sounds-say, two tuning forks- have nearly, but not exactly,
    the same frequencies interfere with each other. A crest may meet a trough at one
    instant in time resulting in destructive interference. However at later time the
    crest may meet a crest at the same point resulting in constructive interference.
    To see how beats arise, consider two sound waves of equalamplitudes and
    slightly different frequencies as shown on the figure below.

    Fig.1. 18: Beats occur as a result of the superposition of two sound waves of slightly different

    frequencies (Cutnell & Johnson, 2006).

    In 1.00 s, the first source makes 50 vibrations whereas the second makes 60. We
    now examine the waves at one point in space equidistant from the two sources.
    The waveforms for each wave as a function of time, at a fixed position, are shown
    on the top graph of Fig. 1.19; the red line represents the 50 Hz wave, and the
    blue line represents the 60 Hz wave. The lower graph in Fig. 1.18 shows the sum
    of the two waves as a function of time. At the time the two waves are in phase
    they interfere constructively and at other time the two waves are completely
    out of phase and interfere destructively. Thus the resultant amplitude is large
    every 0.10 s and drops periodically in between. This rising and falling of the
    intensity is what is heard as beats. In this case the beats are 0.10 s apart. The
    beat frequency is equal to the difference in frequencies of the two interfering
    waves.
    Consider two sound waves of equal amplitude traveling through a medium with
    slightly different frequencies f1 and f2atchosen point x = 0:utnell & Johnson, 2006).

    Using the superposition principle, we find that the resultant wave function at

    this point is 

    The trigonometric identity              write the expression for y as

    We see that the resultant sound for a listener standing at any given point has

    an effective frequency equal to the average frequency given by the expression:               (1.22)

    The frequency of the beats is equal to the difference in the frequencies of the

    two sound waves:


    The interference pattern varies in such a way that a listener hears an alternation
    between loudness and softness. The variation from soft to loud and back to soft
    is called a Beat. The phenomena of beats can be used to measure the unknown

    frequency of a note.

    Example 1.6
    Two identical piano strings of length 0.750 m are each tuned exactly to
    440 Hz. The tension in one of the strings is then increased by 1.0%. If they
    are now struck, what is the beat frequency between the fundamentals of

    the two strings?

    Answer:
    We find the ratio of frequencies if the tension in one string is 1.0% larger

    than the other:     Thus,

    the frequency of the tightened string is 

    and the beat frequency is 

    Quick check 1.4:
    A tuning fork produces a steady 400 Hz tone. When this tuning fork is struck
    and held near a vibrating guitar string, twenty beats are counted in five
    seconds. What are the possible frequencies produced by the guitar string?
    1.2.4 Checking my progress
    1. Is the wavelength of the fundamental standing wave in a tube open
    at both ends greater than, equal to, or less than the wavelength of the
    fundamental standing wave in a tube with one open end and one closed
    end?
    2. You blow across the opening of a bottle to produce a sound. What must
    be the approximate height of the bottle for the fundamental note to be a
    middle C (1.29 m)?
    3. Two loudspeakers are separated by 2.5 m. A person stands at 3.0 m from
    one and at 3.5 m from the other one. Assume a sound velocity of 343
    m/s.What is the minimum frequency to present destructive interference
    at this point? Calculate the other two frequencies that also produce
    destructive interference.
    4. How would you create a longitudinal wave in a stretched spring? Would
    it be possible to create a transverse wave in a spring?
    5. In mechanics, massless strings are often assumed. Why is this not a good
    assumption when discussing waves on strings?
    6. Draw the second harmonic (The second lowest tone it can make.) of a
    one end fixed, one end open pipe. Calculate the frequency of this mode
    if the pipe is 53.2 cm long, and the speed of sound in the pipe is 317 m/s.
    7. Calculate the wavelengths below. The length given is the length of the
    waveform (The picture)

    L = 45 cm                                                             L = 2.67 m                                          L = 68 cm
    8. A guitar string is 64 cm long and has a fundamental Mi frequency of
    330 Hz. When pressing in the first fret (nearest to the tuning keys) see
    fig. the string is shortened in such a way that it plays a Fa note having a
    frequency of 350 Hz. Calculate the distance between this first fret and the

    nut necessary to get this effect.

    9. Why is a pulse on a string considered to be transverse?
    10. A guitar string has a total length of 90 cm and a mass of 3.6 g. From the
    bridge to the nut there is a distance of 60 cm and the string has a tension
    of 520 N. Calculate the fundamental frequency and the first two over
    tones
    1.3 CHARACTERISTICS OF MUSICAL NOTES
    ACTIVITY 1.5: Characteristics of musical notes
    The physical characteristics of a sound wave are directly related to
    the perception of that sound by a listener. Before you read this section
    answer these questions. As you read this section answer again these
    questions. Compare your answer.
    1. What is the difference between the sound of whistle and that of
    drum?
    2. Can you tell which musical instrument is played if the same note is
    played on different instrument without seeing it? Explain
    3. How can you calculate the intensity of a sound wave?
    A musical note is produced by vibrations that are regular and repeating,
    i.e. by periodic motion. Non-periodic motion results in noise which is not
    pleasant to the ear. Many behaviors of musical note can be explained using a
    few characteristics: intensity and loudness, frequency and pitch, and quality or
    timber.
    1.3.1. Pitch and frequency
    The sound of a whistle is different from the sound of a drum. The whistle
    makes a high sound. The drum makes a low sound. The highness or lowness of
    a sound is called its pitch. The higher the frequency, the higher is the pitch. The
    frequency of an audible sound wave determines how high or low we perceive
    the sound to be, which is known as pitch.
    Frequency refers to how often something happens or in our case, the number
    of periodic, compression-rarefaction cycles that occur each second as a sound
    wave moves through a medium and is measured in Hertz (Hz) or cycles/second.
    The term pitch is used to describe our perception of frequencies within the
    range of human hearing.
    If a note of frequency 300 Hz and note of 600 Hz, are sounded by a siren, the
    pitch of the higher note is recognized to be an upper octave of the lower note.
    The musical interval between two notes is an upperoctave if the ratio of their
    frequencies is 2:1. It can be shown that the musical interval between two notes
    depends on the ratio of their frequencies, and not on the actual frequencies.
    Whether a sound is high-pitched or low-pitched depends on how fast something
    vibrates. Fast vibrations make high-pitched sounds. Slow vibrations make lowpitched
    sounds.
    Do not confuse the term pitch with frequency. Frequency is the physical
    measurement of the number of oscillations per second. Pitch is a psychological
    reaction to sound that enables a person to place the sound on a scale from high
    to low, or from treble to bass. Thus, frequency is the stimulus and pitch is the
    response. Although pitch is related mostly to frequency, they are not the same.
    A phrase such as “the pitch of the sound” is incorrect because pitch is not a
    physical property of the sound.The octave is a measure of musical frequency.
    1.3.2 Intensity and amplitude
    A police siren makes a loud sound. Whispering makes a soft sound. Whether a
    sound is loud or soft depends on the force or power of the sound wave. Powerful
    sound waves travel farther than weak sound waves. To talk to a friend across
    the street you have to shout and send out powerful sound waves. Your friend
    would never hear you if you whispered.
    A unit called the decibel measures the power of sound waves. The sound waves
    of a whisper are about 10 decibels. Loud music can have a level of 120 decibels
    or more. Sounds above 140 decibels can actually make your ears hurt. The
    energy carried by a sound wave is proportional to the square of its amplitude.
    The energy passing a unit area per unit time is called the intensity of the wave.
    The intensity of spherical sound wave at a place p is defined as the energy per
    second per m2, or power per m2 flowing normally through an area at X. i.e

             (1.25)

    So the unit of intensity is W /m2 where r is the distance from the source for a

    spherical wave

    Sound intensity level
    To the human ear the change in loudness when the power of a sound increases
    from 0.1 W to 1.0 W is the same as when 1 W to 10 W. The ear responds to the
    ratio of the power and not to their difference. We measure sound level intensity
    in terms of “decibels”. The unit bel is named after the inventor of the telephone,
    Alexander Graham Bell (1847–1922). The decibel is a “relative unit” which is
    actually dimensionless, comparing a given sound to a standard intensity which

    represents the smallest audible sound:             (1.26)

    Where at 1000 Hz is the reference intensity. 0 dB thus represents

    the softest audible sound (threshold of human hearing), while 80 dB (i.e.,
    moderately loud music) represents an intensity which is one hundred million

    times greater.

    Example 1.8

    Two identical machines are positioned the same distance from a worker.

    The intensity of sound delivered by each machine at the location of

    the worker is . Find the sound level heard by the worker (a) when one

    machine is operating and (b) when both machines are operating.

    Answer

    a. The sound level at the location of the worker with one

    machine operating is 

    b. When both machines are operating, the intensity is doubled

    to ; therefore, the sound level now is 

    From these results, we see that when the intensity is doubled,
    the sound level increases by only 3 dB.
    Quick check 1.4:
    A point source emits sound waves with an average power output of 80.0 W.
    a. Find the intensity 3.00 m from the source.
    b. Find the distance at which the sound level is 40 dB.
    ACTIVITY 1.6: Noise or music
    Most people like to listen to music, but hardly anyone likes to listen to
    noise.
    1. What is the physical difference between musical sound and noise?

    2. What is the effect of noise to human being?

    The physical characteristics of a sound wave are directly related to the
    perception of that sound by a listener. For a given frequency the greater the
    pressure amplitude of a sinusoidal sound wave, the greater the perceived
    loudness. The loudness or softness of sound depends on the intensity of the
    sound wave reaching the person concerned. Loudness is a subjective quantity
    unlike intensity.Sound that is not wanted or unpleasant to the ear is called
    noise. High intensity can damage hearing.The higher the intensity, the louder is
    the sound. Our ears, however, do not respond linearly to the intensity. A wave
    that carries twice the energy does not sound twice as loud.
    1.3.3 Quality or timbre
    If the same note is sounded on the violin and then on the piano, an untrained
    listener can tell which instrument is being used, without seeing it. We would
    never mistake a piano for flute. We say that the quality or timbre of note is
    different in each case. The manner in which an instrument is played strongly
    influences the sound quality. Two tones produced by different instruments
    might have the same fundamental frequency (and thus the same pitch) but
    sound different because of different harmonic content. The difference in sound
    is called tone color, quality, or timbre. A violin has a different timbre than a
    piano.
    1.3.4 Checking my progress
    1. Complete each of the following sentences by choosing the correct term
    from the word bank: loudness, pitch, sound quality, echoes, intensity
    and noise
    a. The ------------ of a sound wave depends on its amplitude
    b. Reflected sound waves are called ---------------------------
    c. Two different instruments playing the same note sound different
    because of ------------------
    2. Plane sound wave of frequency 100 Hz fall normally on a smooth wall. At
    what distances from the wall will the air particles have:
    a. Maximum
    b. Minimum amplitude of vibration?
    Give reasons for your answer. The speed of sound in air may be taken as 340
    m/s
    3. A boy whistles a sound with the power of 0.5x10-4w . What will be his
    sound intensity at a distance of 5m?
    4. Calculate the intensity level equivalent to an intensity 1 nW/m2
    5. If the statement is true, write true. If it is false, change the underlined
    word or words to make the statement true.
    a. Intensity is mass per unit volume.
    b. Loudness is how the ear perceives frequency

    c. Music is a set of notes that are pleasing

    1.4 APPLICATIONS OF SOUND WAVES
    ACTIVITY 1.7: Doppler Effect and uses of sound waves
    1. Why does the pitch of a siren change as it moves past you?
    2. How is Doppler’s effect used in communication with satellites?
    3. Explain how is the Doppler’s effect used in Astronomy?
    4. People use sound for other things other than talking and making
    music. In your own word, give more examples and explanations to
    support this statement.
    1.4.1 The Doppler Effect
    Doppler’s effect is the apparent variation in frequency of a wave due to the

    relativemotion of the source of the wave and the observer.

    Fig.1. 19 C.J.Doppler (Douglass, PHYSICS, Principles with applications., 2014)

    The effect takes its name from the Austrian Mathematician Christian Johann
    Doppler (1803-1853), who first stated the physical principle in 1842. Doppler’s
    principle explains why, if a source of sound of a constant pitch is moving toward
    an observer, the sound seems higher in pitch, whereas if the source is moving
    away it seems lower. This change in pitch can be heard by an observer listening

    to the whistle of an express train from a station platform or another train.

    Fig.1. 20: An observer O (the cyclist) moves with a speed vOtoward a stationary point source
    S, the horn of a parked truck. The observer hears a frequency f’ that is greater than the source

    frequency.

    The wavelength is shortened by an amount  vsT , where T is the period
    of the wave. This is simply due to the motion of the source. Since the
    “received” wavelength (λ r

    is related to the “source” wavelength by 


    Knowing the velocity of the moving source of wave ( vs ), you can use the

    equation v = λf to convert the wavelength equations to solve for frequency.

    The received frequency is related to the source frequency by 

    Hence the frequency you hear is higher than the frequency emitted by the
    approaching source.
    Example 1.9
    If a source emits a sound of frequency 400 Hz when at rest, then when
    the source moves toward a fixed observer with a speed of 30 m/s, what
    frequency does the observer hears knowing that the speed of a sound in
    air at room temperature is 343m/s?
    Answer

    The observer hears a frequency of 

    As the source passes you and recedes, the “speed of approach” vs becomes
    negative, and the frequency you hear becomes lower than the frequency emitted
    by the now receding source.

    The frequency of the wave will be: 

    In this case if a source vibrating at 400 Hz is moving away from a fixed observer

    at 30 m/s, the later will hear a frequency of about 

    a. When the source is stationary but you are approaching it at a speed vo.
    The Doppler’s effect also occurs when the source is at rest and the observer is
    in motion. If the observer is travelling toward the source the pitch is higher; and
    if the observer is travelling away from the source, the pitch is lower.
    With a fixed source and moving observer, the distance between wave crests, the
    wavelengthλ , is not changed. But the velocity of the crests with respect to the
    observer is changed. If the observer is moving toward the source, the speed of
    the wave relative to the observer is v′ = v + v0

    Hence, the new frequency is 

    If the observer is moving away from the source, the relative velocity is o v'= v − v

    and 

    Example 1.10
    1. The siren of a police car at rest emits at a predominant frequency
    of 1600 Hz. What frequency will be heard if you were moving with
    speed of 25 m/s?
    a. Toward it?
    b. Away from it?

    Answer


    b. If both the source and receiver are moving
    If both the source and receiver are moving and vs and vo are the speeds with

    which they are approaching each other (respectively), the Doppler shift is

                  (1.31)

    c. Here v is the speed of sound in air; vr  is the speed of the listener (substituted
    as positive if he moves towards the source, as negative if he moves away from
    the source), and vs  is the speed of the source (reckoned as positive if it moves

    towards the listener, as negative if it moves away from the listener.

    Example 1.11
    A car, sounding a horn producing a note of 500 Hz, approaches and
    passes a stationary observer O at a steady speed of 20 m/s. Calculate the
    change in pitch of the note heard by O (speed of sound is 340 m/s)

    Answer:


    For convenience, we can write Doppler’s effect equation as a single

    equation that covers all cases of both source and observer in motion: 

    The upper signs apply if source and/or observer move toward each other. The
    lower signs apply if they are moving apart. The word toward is associated with
    an increase in observed frequency. The words away from are associated with a
    decrease in observed frequency. Although the Doppler’s effect is most typically
    experienced with sound waves, it is a phenomenon that is common to all waves.
    For example, the relative motion of source and observer produces a frequency
    shift in light waves. The Doppler’s effect is used in police radar systems to
    measure the speeds of motor vehicles. Likewise, astronomers use the effect to
    determine the speeds of stars, galaxies, and other celestial objects relative to
    the Earth.
    Example 1.12
    As an ambulance travels east down a highway at a speed of 33.5 m/s, its
    siren emits sound at a frequency of 400 Hz. What frequency is heard by
    a person in a car traveling west at 54.6 m/s
    a. As the car approaches the ambulance and
    b. As the car moves away from the ambulance?
    Answer
    As the ambulance and car approach each other, he person in the car
    hears the frequency

    a. As the vehicles recede from each other, the person hears the frequency

    The change in frequency detected by the person in the car is 475 Hz - 338 Hz
    = 137 Hz, which is more than 30% of the true frequency.
    b. Suppose the car is parked on the side of the highway as the ambulance
    speeds by. What frequency does the person in the car hear as the
    ambulance (a) approaches and (b) recedes?
    Answer
    (a) 443 Hz. (b) 364 Hz.

    The motion of the source of sound affects its pitch.

    Quick check 1.5:
    Middle C on the musical scale has a frequency of 264 Hz. What is the
    wavelength of the sound wave?
    1.4.2 Uses of Ultrasonic
    a. Echolocation
    Some marine mammals, such as dolphin, whales, and porpoises use sound
    waves to locate distant objects. In this process, called echolocation, a dolphin
    produces a rapid train of short sound pulses that travel through the water,
    bounce off distant objects, and reflect back to the dolphin. From these echoes,
    dolphins can determine the size, shape, speed, and distance of their potential
    prey. Experiments have shown that at distance of 114 m, a blindfolded dolphin
    can locate a stainless-steel sphere with a diameter of 7.5 cm and can distinguish
    between a sheet of aluminum and a sheet of copper (Cutnell & Johnson, 2006).
    The Ultrasonic waves emitted by a dolphin enable it to see through bodies of
    other animals and people (Fig.1.21). Skin muscles and fat are almost transparent
    to dolphins, so they see only a thin outline of the body but the bones, teeth and
    gas-filled cavities are clearly apparent. Physical evidence of cancers, tumors,
    heat attacks, and even emotional shake can all be seen by dolphin. What is more
    interesting, the dolphin can reproduce the sonic signals that paint the mental
    image of its surroundings, and thus the dolphin probably communicates its
    experience to other dolphins. It needs no words or symbol for fish, for example,

    but communicates an image of the real thing.

    Fig.1. 21: The Ultrasonic waves emitted by a dolphin enable it to see through bodies of other

    animals and people.

    Bats also use echo to navigate through air.Bats use ultrasonic with frequencies

    up to 100 kHz to move around and hunt (Fig.1.23).


    Fig.1. 22 Bats use ultrasonic with frequencies up to 100 kHz to move around and hunt.

    The waves reflect off objects and return the bat’s ears. The time it takes for the
    sound waves to return tells the bat how far it is from obstacles or prey. The bat
    uses the reflected sound waves to build up a picture of what lies ahead. Dogs,
    cats and mice can hear ultrasound frequencies up to 450 kHz. Some animals
    not only hear ultrasound but also use ultrasonic to see in dark.
    b. In medicine
    The sonogram is device used in medicine and exploits the reflected ultrasound
    to create images. This pulse-echo technique can be used to produce images of
    objects inside the body and is used by Physicians to observe fetuses. Ultrasound
    use a high frequency in the range of 1 MHz to 10 MHz that is directed into the
    body, and its reflections from boundaries or interfaces between organs and
    other structures and lesions in the body are then detected. (Michael, Loannis,
    & Martha, 2006)
    Tumors and other abnormal growths can be distinguished; the action of
    heart valves and the development of a foetus (Fig.1.24) can be examined; and
    information about various organs of the body, such as the brain, heart, liver, and
    kidneys, can be obtained.
    Although ultrasound does not replace X-rays, for certain kinds of diagnosis it is
    more helpful. Some tissues or fluid are not detected in X-ray photographs, but
    ultrasound waves are reflected from their boundaries. Echoes from ultrasound
    waves can show what is inside the body. Echo is a reflection of sound off the

    surface of an object.

    Fig.1. 23: Ultrasound image as an example of using high-frequency sound waves to see within the

    human body (Douglass, PHYSICS, Principles with applications., 2014).

    In medicine, ultrasonic is used as a diagnostic tool, to destroy diseased tissue,
    and to repair damaged tissue.Ultrasound examination of the heart is known as
    echocardiography.
    c. Sonar
    The sonar or pulse-echo technique is used to locate underwater objects and to
    determine distance. A transmitter sends out a sound pulse through the water,
    and a detector receives its reflection, or echo, a short time later. This time interval
    is carefully measured, and from it the distance to the reflecting object can be
    determined since the speed of sound in water is known. The depth of the sea
    and the location of sunken ships, submarines, or fish can be determined in this
    way. Sonar also tells how fast and what direction things are moving. Scientists
    use sonar to make maps of the bottom of the sea. An analysis of waves reflected
    from various structures and boundaries within the Earth reveals characteristic
    patterns that are also useful in the exploration for oil and minerals.
    Radar used at airports to track aircraft involves a similar pulse-echo technique
    except that it uses electromagnetic (EM) waves, which, like visible light, travel
    with a speed of 3 ×108 m/s.
    One reason for using ultrasound waves, other than the fact that they are
    inaudible, is that for shorter wavelengths there is less diffraction so the beam
    spreads less and smaller objects can be detected.
    1.4.3 Uses of infrasonic
    Elephants use infrasonic sounds waves to communicate with one another. Their
    large ears enable them to detect these low frequency sound waves which have
    relatively long wavelengths. Elephants can effectively communicate in this way
    even when they are separated by many kilometers. Some animals, such as this

    young bat-eared fox, have ears adapted for the detection of very weak sounds.

    Fig.1. 24: Some animals, such as this young bat-eared fox, have ears adapted for the detection of

    very weak sounds.

    1.4.4 Checking my progress
    For question 1 to 2: Choose the letter of the best answer
    1. Bats can fly in the dark without hitting anything because
    a. They are flying mammals
    b. Their night vision is going
    c. They are guided by ultrasonic waves produced by them
    d. Of no scientific reason
    2. Bats and dolphins use echolocation to determine distances and find
    prey.
    What characteristic of sound waves is most important for echolocation?
    a. Sound waves reflect when they hit a surface
    b. Sound waves spread out from a source
    c. Sound waves diffract around corner
    d. Sound waves interfere when they overlap
    3. Discuss application of sound waves in medicine and navigation
    4. Explain how sonar is used to measure the depth of a sea
    5. a. What is meant by Doppler Effect?
    b. A police car sound a siren of 1000 Hz as it approaches a stationary
    observer at a speed of 33.5 m/s. What is the apparent frequency
    of the siren as heard by the observer if the speed of sound in air is
    340 m/s.
    c. Give one application of the Doppler Effect.
    END UNIT ASSESSMENT 1
    A. Multiple choices question
    For question 1 to 6, choose the letter of the best answer
    1. Which of the following affects the frequency of wave?
    a. Reflection
    b. Doppler effect
    c. Diffraction
    d. All of the above
    2. Consider the following statements:
    I. Recording of sound on tapes was first invented by Valdemar
    Poulsen.
    II. Audio tapes have magnetic property.
    III. The tapes may also be made of PVC (Polyvinyl-chloride)Of
    these statements:
    a. I, II, and III all are correct.
    b. I, II, and III all are wrong
    c. I and II are correct, III is wrong
    d. I and II are wrong, III is correct
    3. Nodes are
    a. Positions of maximum displacement
    b. Positions of no displacement
    c. A position between no displacement and maximum
    displacement
    d. None of these
    4. Sound waves are
    a. Transverse waves characterized by the displacement of air
    molecules.
    b. Longitudinal waves characterized by the displacement of air
    molecules.
    c. Longitudinal waves characterized by pressure differences.
    d. Both (B) and (C).
    e. (A), (B), and (C).
    5. In which of the following is the wavelength of the lowest vibration
    mode the same as the length of the string or tube?
    a. A string.
    b. A tube closed at one end.
    c. All of the above.
    d. An open tube.
    e. E. None of the above.
    6. When a sound wave passes from air into water, what properties of the
    wave will change?
    a. Frequency.
    b. Wave speed.
    c. Both frequency and wavelength.
    d. Wavelength.
    e. Both wave speed and wavelength.
    B. Structured questions
    1. Does the phenomenon of wave interference apply only to sinusoidal
    waves? Explain.
    2. As oppositely moving pulses of the same shape (one upward, one
    downward) on a string pass through each other, there is one instant at
    which the string shows no displacement from the equilibrium position
    at any point. Has the energy carried b traveling in opposite directions
    on the same string reflect from each other? Explain.
    4. When two waves interfere, can the amplitude of the resultant wave be
    greater than the amplitude of any of the two original waves? Under
    which conditions?
    5. When two waves interfere constructively or destructively, is there any
    gain or loss in energy? Explain.
    6. Explain why your voice seems to sound better than usual when you sing
    in the shower.
    7. An airplane mechanic notices that the sound from a twin-engine aircraft
    rapidly varies in loudness when both engines are running. What could
    be causing this variation from loud to soft?
    8. Explain how a musical instrument such as a piano may be tuned by using
    the phenomenon of beats.
    9. Fill in the gap
    a. As a sound wave or water ripple travels out from its source, its -----
    --------- decreases.
    b. The vibrating air in a/an ----------------------------- has displacement
    antinodes at both ends.
    c. For a /an ……………., the fundamental corresponds to a wavelength
    four times the length of the tube.
    d. The ……………….. refers to the change in pitch of a sound due to
    the motion either of the source or of the observer. If source and
    observer are approaching each other, the perceived pitch is …….. If
    they are moving apart, the perceived pitch is …………….
    10. A bat, moving at 5.00 m/s, is chasing a flying insect. If the bat emits a
    40.0 kHz chirp and receives back an echo at 40.4 kHz, at what speed
    is the insect moving toward or away from the bat? (Take the speed of
    sound in air to be v = 340 m/s.)
    11. If you hear the horn of the car whose frequency is 216 Hz at a frequency
    of 225 Hz, what is their velocity? Is it away from you or toward you? The
    speed of sound is 343 m/s
    12. You run at 12.5 m/s toward a stationary speaker that is emitting a
    frequency of 518 Hz. What frequency do you hear? The speed of sound
    is 343 m/s
    13. If you are moving and you hear the frequency of the speaker at 557
    Hz, what is your velocity? Is it away from or toward the speaker? The
    speed of sound is 343 m/s
    C. Essay type question
    20. Read the following text and answer the question
    Researchers have known for decades that whales sing complicated songs.
    Their songs can last for 30 min and a whale may repeat the song for two or
    more hours. Songs can be heard at a distances of hundreds of kilometers.
    There is evidence that whales use variations in the songs to tell other whales
    about the location of food and predators. Only the male whales sing, which
    has led some researchersto think that songs are also used to attract a male.
    The whale songs may be threatened by noise pollution. in the past 50 years,
    ocean noise has increased due to human activities. Goods are transported
    across the ocean in larger ships than ever before. Large ships use bigger
    engines. They produce low-frequency noise by stirring up air bubbles with
    their propellers. Unfortunately, whales also use low-frequency sound in their
    songs, perhaps because these sounds carry further than high-frequency
    sounds in the ocean. Propeller noise from large ships is loud enough to
    interfere with whale songs at a distance of 20 km.
    Question: Are regulations needed to protect whales from noise?
    In your own words, describe the major issue that needs to be resolved about
    ocean noise pollution. List three arguments for those who think regulations
    should require large ships to reduce noise pollution. List three arguments for

    those who think regulations are not necessary.


  • UNIT 2 APPLICATION OF PHYSICS IN AGRICULTURE

    Fig.2. 1: A farmer spraying rice

    Key unit competence: Evaluate applications of Physics in Agriculture.
    My goals
    • Describe the atmosphere and its constituents.
    • Outline variation of atmospheric pressure, air density and water
    vapour with altitude.
    • Evaluate how heat and mass transfers occur in the atmosphere.
    • Apply knowledge of physics to illustrate changes in water vapour
    atmospheric pressure, and air with altitude.
    • Evaluate and interpret physical properties of soil (soil Texture and
    structure).
    • Evaluate why air, temperature and rainfall limit economical activities
    in Agriculture.
    • Explaining how mechanical weathering and soil erosion impact
    economic activities in agriculture.
    • Explaining clearly how agrophysics plays an important role in the
    limitation of hazards to agricultural objects and environment in our

    country.

    INTRODUCTORY ACTIVITY: Role of machines in agriculture

    It is very important to know the role of Physics in agriculture and
    environment. Knowledge in physics can contribute more in the limitation of
    hazards in agriculture and the environment based on suitable programs of
    transformation and modernization of agriculture in our country.
    Look at the image given in Fig.2.1
    a. What do you observe? Is there any application of prior knowledge
    of Physics learnt before applied on the image? Justify your answer?
    b. Can you suggest the role of machines in agriculture? How do they
    contribute
    in the rapid development of the country programs
    of transformation and modernization of agriculture? Knowing
    different stages of growing plants activities, suggest which stages
    mostly benefit the use of technology!
    Plan it! To get started, brainstorm about your prior knowledge on applications
    of physics in agriculture and try to suggest answers to questions given above

    based on your understanding.

    2.1 ATMOSPHERE AND ITS CONSTITUENTS
    2.1.1 Atmosphere
    ACTIVITY 2.1: How the atmosphere protect life on the earth
    a. Brainstorm and write short notes on constituents of atmosphere
    and explain clearly how the atmosphere of Earth protects life on
    earth.
    b. Why should you care about protecting the atmosphere and
    minimise the long-term changes in the climate?
    c. What can be the use of atmospheric knowledge in evaluating and

    improving agricultural activities?

    The atmosphere of earth is the layer of gases, commonly known as air that

    surrounds the earth. This layer of gases is retained by Earth’s gravity. The

    atmosphere of Earth protects life on Earth by absorbing ultraviolet solar

    radiations that cause cancers and other diseases, warming the surface

    through heat retention (greenhouse effect) and reducing temperature extremes

    between day and night. It also contain the oxygen which human beings, animals

    and plants are using, The atmospheric knowledge can be helpful in evaluating

    and improving the quality of soils and agricultural products as well as the

    technological processes.

    2.1.2 Composition of the Atmosphere

    The atmosphere is composed of a mixture of several gases in differing amounts.

    The permanent gases whose percentages do not change from day to day are

    nitrogen, oxygen and argon. By volume, dry air contains 78.0% nitrogen, 21%

    oxygen, 0.9% argon, 0.04% carbon dioxide, and small amounts of other gases

    called trace gases 0.1% as shown in Fig.2.2

    Gases like carbon dioxide, nitrous oxides, methane, and ozone are trace gases

    that account for about a tenth of one percent of the atmosphere.and plants are using, The atmospheric knowledge can be helpful in evaluating

    and improving the quality of soils and agricultural products as well as the

    technological processes.

    2.1.2 Composition of the Atmosphere

    The atmosphere is composed of a mixture of several gases in differing amounts.

    The permanent gases whose percentages do not change from day to day are

    nitrogen, oxygen and argon. By volume, dry air contains 78.0% nitrogen, 21%

    oxygen, 0.9% argon, 0.04% carbon dioxide, and small amounts of other gases

    called trace gases 0.1% as shown in Fig.2.2

    Gases like carbon dioxide, nitrous oxides, methane, and ozone are trace gases

    that account for about a tenth of one percent of the atmosphere.

    Fig.2. 2Composition of the atmosphere

    Air also contains a variable amount of water vapor, on average around 1% at
    sea level, and 0.4% over the entire atmosphere. Water vapor is unique in that
    its concentration varies from 0-4% of the atmosphere depending on where you
    are and what time of the day it is. In the cold, dry Arctic regions water vapor
    usually accounts for less than 1% of the atmosphere, while in humid, tropical
    regions water vapor can account for almost 4% of the atmosphere. Water vapor
    content is very important in predicting weather.
    Air content and atmospheric pressure vary at different layers, and air suitable
    for use in photosynthesis by terrestrial plants and breathing of terrestrial
    animals is found only in earth’s troposphere.
    The composition of the atmosphere, among other things, determines its ability
    to partly absorb and transmit sunlight radiations and trap infrared radiations,

    leading to potentially minimise the long-term changes in climate.

    2.1.3 Layers of the atmosphere.
    ACTIVITY 2.2: Classifying layers of the atmosphere
    Materials For class demonstration:
    • Chalk board or dry erase board mounted on a wall
    • Chalk or dry erase marker
    • 2-meter piece of string
    • 1000 ml (1 litre) graduated cylinder
    • Four bags of fish gravel or coloured sand (different colours)
    Procedures
    Case1:
    1. Use a model to explore how far the earth’s atmosphere extends
    above the surface of the earth and learn about the thickness of the
    different layers of the atmosphere.
    2. How far do you think the atmosphere extends above us? Tie a dry
    eraser marker or a piece of chalk to one end of the string. Standing
    next to the board, place your foot on the free end of the string and
    draw an arc on the board with a radius of about 1.2 m. Your foot
    represents the center of the earth. The arc represents the surface

    of the Earth.

    Fig.2. 3 A person demonstrating the layers of the atmosphere

    3. Suggest how far the earth’s atmosphere would extend above the
    surface in this drawing. Mark your suggestions on the board above
    the chalk/marker line. Note that it is found that over 90% of the
    earth’s atmosphere is within about 12km of the earth’s surface. The
    distance from the centre of the earth to its surface equals about

    6361 km.

    Case 2:
    1. Use a 1000 ml (1 litter) graduated cylinder and represent the layers by
    using the following amounts of fish gravel or coloured sand found in the
    photo and table below.
    2. Choose what colour you want for each atmospheric layer. Keep in
    mind these are relative proportions and not exact points of departure
    for the different layers. In this scale model, each millilitre of volume
    represents one kilometre of atmosphere layer thickness (for example,
    the troposphere is 10 km thick and is represented by 10 ml of sand or

    gravel in the graduated cylinder).


    Fig.2. 4: Color coding represented in cylinder with the corresponding layers


    Table 2. 1: Atmospheric layers with color code and thickness

    Questions
    1. What atmospheric layers are represented by the different colors?
    2. What atmospheric layer do we live in?
    3. How much thicker is the stratosphere compared to the troposphere?
    4. How much thicker is the thermosphere compared to all the other layers
    combined?
    5. Where in this model would you expect to find clouds?
    6. Where in this model would you expect to find mounts Everest and
    Kalisimbi?
    7. Where in this model would you expect to find a satellite?
    8. Where in this model would you expect to find the space shuttle?

    9. Where in this model is the ozone layer?

    Earth’s atmosphere has a series of layers, each with its own specific
    characteristics and properties. Moving upward from ground level, these layers
    are named the troposphere, stratosphere, mesosphere, thermosphere and
    exosphere.
    The above activity demonstrates the relative thickness of the thin section of the
    atmosphere that includes the troposphere and stratosphere. These layers are
    essential to all life on Earth. Over 99% of the mass of the Earth’s atmosphere
    is contained in the two lowest layers: the troposphere and the stratosphere.
    Most of the Earth’s atmosphere (80 to 90%) is found in the troposphere, the
    atmospheric layer where we live (Cunningham & William, 2000).
    This layer, where the Earth’s weather occurs, is within about 10 km of the
    Earth’s surface. The stratosphere goes up to about 50 km. Gravity is the reason

    why atmosphere is more dense closer to the Earth’s surface.

    Fig.2. 5: Illustration of layers from the core to the atmosphere

    While we may think of the atmosphere as a vast ocean of air around us, it is very
    thin relative to the size of the earth. The “thickness” of the atmosphere, or the
    distance between the earth’s surface and the “top” of the atmosphere, is not an
    exact measure. Although air is considered as a fluid, it does not have the same
    well-defined surface as water does. The atmosphere just fades away into space
    with increasing altitude.
    Description of layers of earth’s atmosphere
    A. Troposphere
    This is the lowest layer of our atmosphere starting at ground level; it extends
    upward to about 10 km above the sea level. We live in the troposphere, and
    nearly all weather occurs in this lowest layer. Most clouds appear here, mainly

    because 99% of the water vapor in the atmosphere is found in the troposphere.

    Air pressure drops and temperatures get colder, as you climb higher in the
    troposphere.
    B. Stratosphere
    The stratosphere extends from the top of the troposphere to about 50 km above
    the ground. The infamous ozone layer is found within the stratosphere. Ozone
    molecules in this layer absorb high-energy ultraviolet (UV) light from the sun,
    converting the ultraviolet energy into heat.
    Unlike the troposphere, the stratosphere actually gets warmer the higher
    you go! That trend of rising temperatures with altitude means that air in the
    stratosphere lacks the turbulence and updrafts of the troposphere beneath.
    Commercial passenger jets fly in the lower stratosphere, partly because this
    less-turbulent layer provides a smoother ride.
    C. Mesosphere
    It extends upward to a height of about 85 km above our planet. Most meteors
    burn up in the mesosphere. Unlike the stratosphere, temperatures once again
    grow colder as you rise up through the mesosphere. The coldest temperatures
    in earth’s atmosphere, about -90° C, are found near the top of this layer. The air
    in the mesosphere is far too thin to breathe; air pressure at the bottom of this
    layer is well below 1% of the pressure at sea level, and continues dropping as
    you go higher.
    D. Thermosphere
    High-energy X-rays and ultraviolet radiations from the Sun are absorbed in the
    thermosphere, raising its temperature to hundreds or at times thousands of
    degrees. Many satellites actually orbit Earth within the thermosphere! Variations
    in the amount of energy coming from the Sun exert a powerful influence on
    both the height of the top of this layer and the temperature within it. Because of
    this, the top of the thermosphere can be found anywhere between 500 km and
    1 000 km above the ground. Temperatures in the upper thermosphere can
    range from about 500 ° C to 2 000 °C or even higher.
    E. Exosphere
    Although some experts consider the thermosphere to be the uppermost layer of
    our atmosphere, others consider the exosphere to be the actual “final frontier”
    of Earth’s gaseous envelope. As you might imagine, the “air” in the exosphere is
    very thin, making this layer even more space-like than the thermosphere.
    In fact, air in the exosphere is constantly “leaking” out of earth’s atmosphere
    into outer space. There is no clear-cut upper boundary where the exosphere
    finally fades away into space. Different definitions place the top of the exosphere
    somewhere between 100 000 km and 190 000 km above the surface of earth.
    The latter value is about halfway to the moon!
    F. Ionosphere
    The ionosphere is not a distinct layer like the others mentioned above.
    Instead, the ionosphere is a series of regions in parts of the mesosphere and
    thermosphere where high-energy radiation from the sun has ionized atoms
    and molecules. The ions formed in this way are responsible of the naming of

    this region as the ionosphere and endowing it with some special properties.

    ACTIVITY 2.3: Classifying layers of the atmosphere
    Observe scale models of the atmosphere on fig.3.3 below and its layers.
    Note the height of earth’s atmosphere as compared to the size of
    the planet overall and the relative thickness of each of the four main
    layers of the atmosphere. Interpret the graph and Use it to answer

    questions below:

    Fig.2. 6: Layers of the atmosphere.

    Questions:
    a. Outline the economic activities taking place in the layers
    represented above?
    b. Why is it very important to have ozone layer in the layers
    close to the earth surface?
    c. Explain why it is advisable to travel in troposphere and
    stratosphere than in other layers of the atmosphere?
    d. Explain clearly why the rocket and aeroplanes decide to move

    in the corresponding layers of the atmosphere?

    2.1.4 Checking my progress
    1. Use the fruit question suggested in the procedure and respond in writing
    or with a picture instead of simply orally in class. Think of the fruit as the
    size of the Earth and the skin of the fruit represents the thickness of the
    atmosphere. Make a labelled diagram in your note book illustrating the
    most important point of the lesson and the reason why the atmosphere
    is considered as the skin of the fruit?
    2. Imagine that you are in an orbit around a planet one half the size and
    mass of the Earth. Explain how I would expect the atmosphere of the new
    planet to be different from my planet?
    3. What is the structure and composition of the atmosphere?
    4. How does solar energy influence the atmosphere?
    5. How does the atmosphere interact with land and oceans?
    6. Outline two most important layers that are essential to all life on earth?
    Explain clearly to support your answer.
    2.2 HEAT AND MASS TRANSFER
    2.2.1 Modes of Heat Transfer
    ACTIVITY 2.4: Describing the different modes of heat transfer
    in the atmosphere

    Brainstorm on modes of heat transfer and explain clearly how each

    affects agricultural activities?

    Heat transfer is concerned with the exchange of thermal energy through a
    body or between bodies which occurs when there is a temperature difference.
    When two bodies are at different temperatures, thermal energy transfers from
    the one with higher temperature to the one with lower temperature. Naturally
    heat transfers from hot to cold. A small amount of the energy that was directed
    towards the earth from the sun is absorbed by the atmosphere, a larger amount
    (about 30%) is reflected back to space by clouds and the Earth’s surface, and
    the remaining is absorbed at the planet surface and then partially released as
    heat. Energy is transferred between the Earth’s surface and the atmosphere
    in a variety of ways, including radiation, conduction, and convection. The
    figure below uses a camp stove to summarize the various mechanisms of heat
    transfer. If you were standing next to the camp stove, you would be warmed by
    the radiation emitted by the gas flame. A portion of the radiant energy generated
    by the gas flame is absorbed by the frying pan and the pot of water.
    By the process of conduction, this energy is transferred through the pot and pan.
    If you reached for the metal handle of the frying pan without using a potholder,
    you would burn your fingers! As the temperature of the water at the bottom
    of the pot increases, this layer of water moves upward and is replaced by cool
    water descending from above. Thus convection currents that redistribute the

    newly acquired energy throughout the pot are established.

    Fig.2. 7: Camp stove to summarize the various mechanisms of heat transfer.

    As in this simple example using a camp stove, the heating of the Earth’s
    atmosphere involves radiation, conduction, and convection, all occurring
    simultaneously. A basic theory of meteorology is that the Sun warms the ground
    and the ground warms the air. This activity focuses on radiation, the process
    by which the Sun warms the ground. Energy from the Sun is the driving force
    behind weather and climate.
    Quick check 2.1
    What do trees, snow, cars, horses, rocks, centipedes, oceans, the atmosphere,
    and you have in common?
    Each one is a source of radiation to some degree. Most of this radiation is
    invisible to humans but that does not make it any less real.
    Radiation is the transfer of energy by electromagnetic waves. The transfer of
    energy from the Sun across nearly empty space is accomplished primarily by
    radiation. Radiation occurs without the involvement of a physical substance
    as the medium. The Sun emits many forms of electromagnetic radiation in

    varying quantities.


    Fig.2. 8: The spectrum of electromagnetic radiations emitted by the sun

    About 43% of the total radiant energy emitted from the Sun is in the visible
    part of the spectrum. The bulk of the remainder lies in the near-infrared (49%)
    and ultraviolet (7%) bands. Less than 1% of solar radiation is emitted as x-rays,
    gamma rays, and radio waves.
    A perfect radiating body emits energy in all possible wavelengths, but the wave
    energies are not emitted equally in all wavelengths; a spectrum will show a
    distinct maximum in energy at a particular wavelength depending upon the
    temperature of the radiating body. As the temperature increases, the maximum
    radiation occurs at shorter wavelengths.
    The hotter the radiating body, the shorter the wavelength of maximum radiation.
    For example, a very hot metal rod will emit visible radiation and produce a
    white glow. On cooling, it will emit more of its energy in longer wavelengths
    and will glow a reddish color. Eventually no light will be given off, but if you
    place your hand near the rod, the infrared radiation will be detectable as heat.
    The amount of energy absorbed by an object depends upon the following:
    • The object’s absorptivity, which, in the visible range of wavelengths, is
    a function of its color
    • The intensity of the radiation striking the object
    Every surface on Earth absorbs and reflects energy at varying degrees, based
    on its color and texture. Darker-colored objects absorb more visible radiation,
    whereas lighter-colored objects reflect more visible radiation. These concepts

    are clearly discussed in unit two.

    2.2.2 Environmental heat energy and mass transfer


    Fig.2. 9: Illustration of interactions of solar radiations with different constituents of the atmosphere.

    Practically all of the energy that reaches the earth comes from the sun.
    Intercepted first by the atmosphere, a small part is directly absorbed,
    particularly by certain gases such as ozone and water vapor. Some energy is
    also reflected back to space by clouds and the earth’s surface.
    In the atmosphere, convection includes large- and small-scale rising and
    sinking of air masses.. These vertical motions effectively distribute heat and
    moisture throughout the atmospheric column and contribute to cloud and
    storm development where rising motion occurs) and dissipation where sinking

    motion occurs.

    2.2.3 Water vapour in the atmosphere.
    ACTIVITY 2.5: Impact of water vapor in agricultural activities
    1. Brainstorm on water vapor in the atmosphere and explain clearly
    how it impacts on agricultural activities?
    2. Does water vapor play an important role in the atmosphere? Justify
    your answer with clear reasons.
    When water vapor condenses onto a surface, a net warming occurs on that
    surface. The water molecule brings heat energy with it. In turn, the temperature
    of the atmosphere drops slightly. In the atmosphere, condensation
    produces clouds, fog and precipitation (usually only when facilitated by cloud
    condensation nuclei).

    The role of water vapor in the atmosphere

    Water vapor plays a dominant role in the radiative balance and the hydrological
    cycle. It is a principal element in the thermodynamics of the atmosphere as it
    transports latent heat and contributes to absorption and emission in a number
    of bands. It also condenses into clouds that reflect and adsorb solar radiation,
    thus directly affecting the energy balance.
    In the lower atmosphere, the water vapor concentrations can vary by orders of
    magnitude from place to place.
    2.2.4 Variation in Atmospheric Pressure
    Variation with height or vertical variation: The pressure depends on the
    density or mass of the air. The density of air depends on its temperature,
    composition and force of gravity. It is observed that the density of air decreases
    with increase in height so the pressure also decreases with increase in height.
    Horizontal variation of pressure: The horizontal variation of atmospheric
    pressure depends on temperature, extent of water vapor, latitude and land and
    water relationship.
    Factors affecting atmospheric pressure:
    1. Temperature of air
    2. Altitude
    3. Water vapor in air
    4. Gravity of the earth.
    Effect of atmospheric pressure in agricultural activities
    The pressure exerted by the atmosphere of the earth’s surface is called
    atmospheric pressure. Generally, in areas of higher temperature, the
    atmospheric pressure is low and in areas of low-temperature the pressure
    is high. Atmospheric pressure has no direct influence on crop growth. It is,
    however an important parameter in weather forecasting.
    2.2.5 Air density and water vapour with altitude
    ACTIVITY 2.6: Effect of air density in the atmosphere

    Brainstorm on air density and explain clearly its affects in the earth’s
    atmosphere?
    The density of air (air density) is the mass per unit volume of earth’s
    atmosphere.
    Air density, like air pressure, decreases with increasing altitude.

    It also changes with variation in temperature and humidity. At sea level and at

    15 °C air has a density of approximately 1.225 kg/m3.
    Air density and the water vapor content of the air have an important effect
    upon engine performance and the takeoff characteristics of air-craft. Some of
    the effects these two factors have upon engine takeoff, and the methods for
    computing these elements from a meteorological standpoint. Pressure altitude,
    density altitude, vapor pressure, and specific humidity in the atmosphere are
    determined using a Density Altitude Computer.
    Pressure altitude: Pressure altitude is defined as the altitude of a given
    atmospheric pressure in the standard atmosphere. The pressure altitude of
    a given pressure is, therefore, usually a fictitious altitude, since it is equal to
    true altitude only rarely, when atmospheric conditions between sea level and
    the altimeter in the aircraft correspond to those of the standard atmosphere.
    Aircraft altimeters are constructed for the pressure-height relationship that

    exists in the standard atmosphere.

    2.2.6 Checking my progress
    1. Why does atmospheric pressure change with altitude?
    2. The graph below gives an indication of how pressure varies non-linearly

    with altitude. Use the graph to answer the following questions:

    Fig.2. 10: A graph of altitude vs pressure

    a. Explain what happens to pressure if the altitude reduces?
    b. Estimate the atmospheric pressure when someone is at an altitude of

    40 km above sea level.

    2.3 PHYSICAL PROPERTIES OF SOIL
    ACTIVITY 2.7: How the surface of earth reflects and absorbs heat
    Perform the activity to investigate how different surfaces of the
    earth reflect and absorb heat and apply this knowledge to realworld
    situations. It justifies that the physical characteristics of the
    Earth’s surface affect the way that surface absorbs and releases heat
    from the Sun.

    Materials needed in demonstration


    Procedures

    1. a. Brainstorm on the already known concepts about how the color
    and type of material affects how hot it gets in the sunshine. Try to
    think about these questions. When it is a hot day, what color shirt
    would you wear to keep cool and why? During the summer, what
    would it feel like to walk on gravel with no shoes?
    b. In performing activity, explore how different types of surfaces
    found at the earth’s surface (such as sand, soil, and water) heat
    up when the sun’s energy reaches them, and how they cool down
    when out of the sunshine.
    c. Note that this experiment uses materials to model sunshine
    and earth materials. Observe the materials and realize how each
    material relates to the earth system. (The lamp represents the
    sun in this model. The sand represents beaches, sand dunes, and
    rocks. The potting soil represents large areas of soil outdoors. And
    the water represents lakes, rivers, and the ocean.)
    2. Fill the pie pans to the same level, one with dark soil, one with light
    sand, and one with water.
    3. Place the pie pans on a table or desk and position the lamp about

    30.48 cm above them. (Do not turn on the lamp yet.)


    Fig.2. 11: Arrangement of pie pans to investigate the absorption of solar radiation.

    Checking skills Questions
    1. Which material absorbed more heat in the first ten minutes?
    2. Which material lost the most heat in the last ten minutes?
    3. Imagine that it is summer and that the Sun is shining on the ocean and
    on a stretch of land.
    a. Which one will heat up more during the day?
    b. Which one will cool more slowly at night? Explain.
    4. Imagine three cities in the desert, all at about the same altitude and
    latitude. Which city would likely have the highest average summer air
    temperature and why?
    • One city (A) is surrounded by a dark-colored rocky surface.
    • Another city (B) is surrounded by a light-colored sandy surface.
    • The third city (C) is built on the edge of a large man-made desert
    lake.
    5. The Earth’s surface tends to lose heat in winter. Which of the above cities
    would have the warmest average winter temperature? Why?
    6. Since the Sun is approximately 93 million miles from the Earth and space
    has no temperature, how do we get heat from the Sun?
    Physical properties of a soil that affect a plant’s ability to grow include: Soil
    texture,
    which affects the soil’s ability to hold onto nutrients (cation exchange
    capacity) and water. Texture refers to the relative distribution of the different
    sized particles in the soil. It is a stable property of soils and, hence, is used in
    soil classification and description.Soil structure, which affects aeration, waterholding
    capacity, drainage, and penetration by roots and seedlings, among other
    things. Soil structure refers to the arrangement of soil particles into aggregates
    and the distribution of pores in between. It is not a stable property and is
    greatly influenced by soil management practices.
    2.3.1 Soil texture
    ACTIVITY 2.8
    Soil texture is determined by three proportions of the soil. Brainstorm
    and try to answer questions using knowledge gained.
    a. Outline three proportions of the soil?
    b. What does the underlined word mean?
    Soil texture, or the ‘feel’ of a soil, is determined by the proportions of sand, silt,
    and clay in the soil. When they are wet, sandy soils feel gritty, silky soils feel
    smooth and silky, and clayey soils feel sticky and plastic, or capable of being
    moulded. Soils with a high proportion of sand are referred to as ‘light’, and
    those with a high proportion of clay are referred to as ‘heavy’.
    The names of soil texture classes are intended to give you an idea of their
    textural make-up and physical properties. The three basic groups of texture
    classes are sands, clays and loams.A soil in the sand group contains at least
    70% by weight of sand. A soil in the clay group must contain at least 35% clay
    and, in most cases, not less than 40%. A loam soil is, ideally, a mixture of sand,
    silt and clay particles that exhibit light and heavy properties in about equal
    proportions, so a soil in the loam group will start from this point and then

    include greater or lesser amounts of sand, silt or clay.

    2.3.2 Soil structure
    ACTIVITY 2.9
    a. It is known that soil structure contains soil particles and pores
    and is classified under physical properties of soil. Brainstorm and
    write short notes on soil structure.
    Use the knowledge gained in part (a) above to answer questions in part (b).
    b. (i) List the elements found in soil particles.
    (ii)What do the underlined words mean?
    (iii)Explain the role of pores in soil structure that improves
    capillary action in plant growth.
    Structure is the arrangement of primary sand, silt and clay particles into
    secondary aggregates called peds or structural units which have distinct shapes
    and are easy to recognize. These differently shaped aggregates are called the
    structural type.
    There are 5 basic types of structural units:
    • Platy: Plate-like aggregates that form parallel to the horizons like
    pages in a book. This type of structure may reduce air, water and root
    movement.
    • Blocky: Two types--angular blocky and sub angular blocky. These
    types of structures are commonly seen in the B horizon. Angular is
    cube-like with sharp corners while sub angular blocky has rounded
    corners.
    • Prismatic: Vertical axis is longer than the horizontal axis. If the top
    is flat, it is referred to as prismatic. If the top is rounded, it is called
    columnar.
    • Granular: Peds are round and pourous, spheroidal. This is usually the
    structure of A horizons.
    • Structureless: No observable aggregation or structural units.
    Good soil structure means the presence of aggregations which has positive
    benefits for plant growth. These benefits arise from the wider range of pore
    sizes which result from aggregation. The nature of the pore spaces of a soil
    controls to a large extent the behavior of the soil water and the soil atmosphere.
    It influences the soil temperature. All these affect root growth, as does the
    presence of soil pores of appropriate size to permit root elongation. Favorable
    soil structure is therefore crucial for successful crop development. The
    destruction of soil structure may result in a reduction in soil porosity and/or
    change to the pore size distribution.
    Soil structure refers to the arrangement of soil particles (sand, silt and clay)
    and pores in the soil and to the ability of the particles to form aggregates.
    Aggregates are groups of soil particles held together by organic matter or
    chemical forces. Pores are the spaces in the soil. The pores between the
    aggregates are usually large (macro pores), and their large size allows good
    aeration, rapid infiltration of water, easy plant root penetration, and good
    water drainage, as well as providing good conditions for soil micro-organisms
    to thrive. The smaller pores within the aggregates or between soil’s particles
    (micro pores) hold water against gravity (capillary action) but not necessarily
    so tightly that plant cannot extract the water.
    A well-structured soil forms stable aggregates and has many pores (Fig.3.12 A).
    it is friable, easily worked and allows germinating seedlings to emerge and to
    quickly establish a strong root system. A poorly structured soil has either few
    or unstable aggregates and few pore spaces (Fig.3.12 B). This type of soil can
    result in unproductive compacted or waterlogged soils that have poor drainage
    and aeration. Poorly structured soil is also more likely to slake and to become

    eroded.

    Fig.3. 12: Different soil structures: well structured and poorly structured soil.

    2.3.3 Checking my progress:
    1. Explain the physical properties of Soil and explain clearly how each
    impact agricultural activities?
    2. (a) Explain how the weathering of rocks contributes to soil formation.
    (b) Explain the following terms as used in the context of soil and plant
    growth.
    I. Well structured soil
    II. Poor structured soil
    (c) The following table shows the water content of three soil samples.

    Use the table to answer questions that follows:


    Analytical Questions:
    I. What is the percentage of available water in sample A?
    II. Which sample would be the most suitable for a crop suffering a
    drought during the growing season?
    III. Which sample would be the most suitable for a crop growing
    during a rainy season?
    (d) Describe an experiment to compare the capillarity of two contrasting

    soils.

    2.4 MECHANICAL WEATHERING
    2.4.1 Concepts of mechanical weathering
    ACTIVITY 3.10:Exploring Mechanical Weathering
    Mechanical rock weathering is an important part of the formation of
    both soils and new rocks, and an important part of the entire rock cycle.
    The activity explores what causes rocks to break down.
    Materials:
    • Coffee can with lid
    • Rocks

    • Dark-coloured construction paper

    Fig.2. 13 Coffee can with lid

    Procedures
    Place a handful of rocks on a piece of dark-coloured construction paper.
    Observe the rocks and take notes on their appearance. Place the rocks
    in a coffee can. Put the lid on the can and shake the can forcefully for 2
    minutes, holding the lid tightly shut. Pour the rocks onto the construction
    paper. Observe them and take notes on any changes in their appearance.
    Use the skills gained above to answer the following questions:
    d. What happened to the rocks and why?

    e. What forces in nature might affect rocks in similar ways?

    Briefly explain what causes mechanical weathering?
    Earth’s surface is constantly changing. Rock is integrated and decomposed,
    moved to lower elevations by gravity, and carried away by water, wind, or
    ice. When a rock undergoes mechanical weathering, it is broken into smaller
    and smaller pieces of sediment and dissolved minerals; each retaining the
    characteristics of the original material. The result is many small pieces from a
    single large one.
    Weathering takes place in two ways: physical weathering and chemical
    weathering. Physical and chemical weathering can go on at the same time.
    Weathering is thus the response of Earth’s materials to change environment.
    Weathering is the first step in the breakdown of rock into smaller fragments.
    This process is critical to the formation of landscapes and many other geological
    processes. Our discussion will focus on mechanical weathering. Mechanical
    weathering is the physical breaking up of rocks into smaller pieces.
    2.4.2 Causes of mechanical weathering
    Temperature change
    ACTIVITY 3.11:Effects of temperature on mechanical weathering
    a. Brainstorm on the effects of temperature in mechanical weathering
    and explain clearly its impacts on soil formation and agricultural
    activities?
    b. Explain how thermal expansion and contraction affect mineral
    composition?
    As the water evaporates, the salt is left behind. Over time, these salt deposits build
    up, creating pressure that can cause rocks to split and weaken. Temperature
    changes also affect mechanical weathering. As temperatures heat up, the

    rocks themselves expand.

    Fig.2. 14 Illustration of mechanical weathering

    Temperature is an essential part of rock creation, modification and destruction.
    Heating a rock causes it to expand, and cooling causes it to contract. Repeated
    swelling and shrinking of minerals that have different expansion and
    contraction rates should exert some stress on the rock’s outer shell.
    Thermal expansion and contraction of minerals
    Thermal expansion is the tendency of matter to change in shape, area, and
    volume in response to a change in temperature. Thermal expansion due to
    the extreme range of temperatures can shatter rocks in desert environments.
    Temperature is a monotonic function of the average molecular kinetic energy
    of a substance. When a substance is heated, the kinetic energy of its molecules
    increases. Thus, the molecules begin vibrating more and usually maintain a
    greater average separation.
    Materials which contract with increasing temperature are unusual; this effect
    is limited in size, and only occurs within limited temperature ranges. The
    relative expansion (also called strain) divided by the change in temperature is
    called the material’s coefficient of thermal expansion and generally varies
    with temperature. Materials expand or contract. when subjected to changes in
    temperature. Most materials expand when they are heated, and contract when
    they are cooled. When free to deform, concrete will expand or contract due
    to fluctuations in temperature. Concrete expands slightly as temperature rises
    and contracts as temperature falls. Temperature changes may be caused by
    environmental conditions or by cement hydration.
    Thermal expansion and contraction of concrete varies primarily with aggregate
    type (shale, limestone, siliceous gravel and granite), cementitious material
    content, water cement ratio, temperature range, concrete age, and ambient
    relative humidity. Of these factors, aggregate type has the greatest influence on
    the expansion and contraction of concrete.
    Quick Check 2.2
    1. How does climate affect the rate of weathering?
    2. What is the process that breaks down rocks?
    a. Effects of temperature and moisture changes on weathering
    At high elevations, cold night time temperatures during much of the year can
    produce relentless freeze-thaw cycles. This process explains the presence of
    broken boulders and stony fragments that litter mountaintops. And, the minerals
    in volcanic rock that formed at the highest temperatures and pressures are the

    most vulnerable to chemical weathering at Earth’s surface.

    In many locations, changes in temperature and moisture content of the
    environment cause significant physical weathering. When rock is warmed,
    it expands; when it cools, it contracts. In some regions, rocks are heated to
    relatively high temperatures during the day and then cooled to much lower
    temperatures during the night. The constant expansion and contraction of the
    rocks may result in pieces being broken off. Temperature also affects the land
    as the cool nights and hot days always cause things to expand and contract.
    That movement can cause rocks to crack and break apart.
    The most common type of mechanical weathering is the constant freezing, and
    thawing of water. In liquid form, water is capable of penetrating holes, joints,
    and fissures within a rock. As the temperature drops below zero celcius, this
    water freezes. Frozen water expands compared to its liquid form. The result is
    that the holes and cracks in rocks are pushed outward. Even the strongest rocks
    are no match for this force.
    As temperatures heat up, the rocks themselves expand. As the temperatures
    cool down, rocks contract slightly. The effect can be the weakening of the rock
    itself which induces mechanical weathering. It breaks rock into smaller pieces.
    These smaller pieces are just like the bigger rock, but smaller. That means the
    rock has changed physically without changing its composition. The smaller
    pieces have the same minerals, in just the same proportions as the original
    rock.
    b. Ice wedging
    There are many ways that rocks can be broken apart into smaller pieces.
    Ice wedging is the main form of mechanical weathering in any climate that
    regularly cycles above and below the freezing point (Fig.2.15). Ice wedging
    works quickly, breaking apart rocks in areas with temperatures that cycle above

    and below freezing in the day and night.

    Fig.2. 15 Ice wedging.

    Explanation of figure 3.15:
    (A) water seeps into cracks and fractures in rock, (B) when the water freezes, it
    expands about 9% in volume, which wedges apart the rock, (C) with repeated
    freeze cycles, rock breaks into pieces.
    Ice wedging breaks apart so much, rocks with large piles of broken rock are
    seen at the base of a hillside, as rock fragments separate and tumble down. Ice
    wedging is common in Earth’s polar regions and mid latitudes, and also at higher
    elevations in the mountains. Water has the unique property of expanding about
    9% when it freezes. This increase in volume occurs because, as ice form, the
    water molecules arrange themselves into a very open crystalline structure. As a
    result, when water freezes, it expands and exerts a tremendous outward force.
    This can be verified by completely filling a container with water and freezing it.
    After many freezing cycle, the rock is broken into pieces. This process is called
    frost wedging also as known as Freeze-thaw weathering as shown in Fig.3.13.
    This occurs when water gets into the small holes and gaps in rocks. If the water
    in the gap freezes, it expands, splitting the existing gaps into wider cracks. When
    the water thaws, the wider gaps allow even more water to enter the rock and
    freeze. Frost wedging can repeat over months or years, turning microscopic
    gaps in the rock into large cracks. Ice has more volume than liquid water, so
    the cracks are forced wider. Then, more water accumulates in the cracks the
    next day, which freeze at night to widen the cracks further. When this happens
    repeatedly, the rock eventually breaks apart along the crevices.
    Frost heaving, a similar process to frost wedging, occurs when a layer of ice
    forms under loose rock or soil during the winter, causing the ground surface to
    bulge upward. When it melts in the spring, the ground surface collapses.
    c. Abrasion
    ACTIVITY 2.12: Importance of abrasion in real life situations
    With the help of knowledge gained in the concepts above, explain how
    abrasion is formed and suggest its importance in real life situations?
    The word ‘abrasion’ literally means scraping of the surface of an object. This
    is exactly what happens with abrasion of rocks. Weathering by abrasion is
    responsible for the creation of some of the largest deserts in the world. The
    rock’s surface is exposed to blown sands - high velocity winds which blow

    throughout the day while carrying large sand particle

    The sand blasts against the surfaces of the rocks, undercutting and deflating
    them. As a result, smaller rock particles are formed, which when exposed to
    further sand abrasion become sand particles themselves.
    Abrasion makes rocks with sharp or jagged edges smooth and round. If you
    have ever collected beach glass or cobbles from a stream, you have witnessed
    the work of abrasion (Fig.2.16 below). Rocks on a beach are worn down by

    abrasion as passing waves cause them to strike each other

    Fig.2. 16 Smooth round rocks

    In abrasion, one rock bumps against another rock. The following are the causes
    of abrasion;
    • Gravity causes abrasion as a rock tumbles down a mountainside or cliff.
    • Moving water causes abrasion as particles in the water collide and
    bump against one another.
    • Strong winds carrying pieces of sand can sandblast surfaces.
    • Ice in glaciers carries many bits and pieces of rock. Rocks embedded
    at the bottom of the glacier scrape against the rocks.
    Therefore abrasion occurs when the surface of rocks is exposed to water or
    wind. These elements can carry tiny particles of sediment or rock that then
    collide against the rock’s surface. When these particles rub against the rock’s
    surface, they break off tiny pieces of the rock. Over time, abrasion can wear
    down and smooth extremely large sections of the rock.
    d. Biological activity
    Weathering is also accomplished by the activities of organisms, including
    plants, burrowing animals, and humans. Plant roots in search of minerals and
    water grow into fractures, and as the roots grow they wedge the rock apart .
    Burrowing animals further break down the rock by moving fresh material to
    the surface, where physical and chemical process can more effectively attack
    it. Decaying organisms also produce acids, which contribute to chemical
    weathering .
    2.4.3 Factors influencing the type and rate of rock weathering
    ACTIVITY 2.13
    Brainstorm and classify clearly the factors affecting the rate of weathering?
    Several factors influence the type and rate of rock weathering. By breaking a rock
    into smaller pieces, the amount of surface area exposed to chemical weathering
    is increased. The presence or absence of joints can be significant because they
    influence the ability of water to penetrate the rock. Other important factors
    include the mineral makeup of rocks and climate.
    a. Climate
    The amount of water in the air and the temperature of an area are both part of
    an area’s climate. Moisture speeds up chemical weathering. Weathering occurs
    fastest in hot, wet climates. It occurs very slowly in hot and dry climates. Without
    temperature changes, ice wedging cannot occur. In very cold, dry areas, there
    is little weathering.
    b. Surface area
    Most weathering occurs on exposed surfaces of rocks and minerals. The more
    surface area a rock has, the more quickly it will weather. When a block is cut
    into smaller pieces, it has more surface area. So, therefore, the smaller pieces of
    a rock will weather faster than a large block of rock
    c. Rock composition
    Headstones of granite, which is composed of silicate minerals, are relatively
    resistant to chemical weathering. The minerals that crystallize first form under
    much higher temperatures than those which crystallize last. Consequently,
    the early formed minerals are not as stable at Earth’s surface, where the
    temperatures are different from the environment in which they formed. Olivine
    crystalizes first and is therefore the least resistant to chemical weathering,
    whereas quartz, which crystallizes last, is the most resistant.
    d. Pollution speeds up weathering
    Factories and cars release carbon dioxide and other gases into the air. These
    gases dissolve in the rainwater, causing acid rain to form. Acid rain contains
    nitric and sulfuric acid, causing rocks and minerals to dissolve faster.
    e. Soil erosion and soil deposition
    ACTIVITY 2.14: Soil erosion
    Look at the figure below that represents soil erosion. Carefully study

    the figure and answer the following questions:


    Fig.2. 17 The erosive force of wind on an open field

    a. What do you think caused water to get contaminated as shown in
    fig below
    b. How often have you seen water looking like that in your area.
    What was the cause?
    c. What scientific phenomena that explains the washing away of the
    top soil.
    d. how does the phenomena explained in c) above affect agriculture?
    e. Suggest possible measures that can be taken to reduce or stop the
    phenomenon explained in c) above
    Soil covers most land surfaces. Along with air and water, it is one of our most
    indispensableresources. Soil is a combination of mineral and organic matter.
    Soil erosion is a naturally occurring process that affects all landforms. In
    agriculture, soil erosion refers to the wearing away of a field’s topsoil by the
    natural physical forces of water and wind or through forces associated with
    farming activities.
    Erosion is incorporation and transportation of material by a mobile agent,
    usually water, wind, or ice. Erosion whether it is by water and wind, involves
    three distinct actions – soil detachment, movement and deposition. Topsoil,
    which is high in organic matter, fertility and soil life, is relocated elsewhere
    “on-site” where it builds up over time or is carried “off-site” where it fills in
    drainage channels. Soil erosion reduces cropland productivity and contributes
    to the pollution of adjacent watercourses, wetlands and lakes. Soil erosion
    can be a slow process that continues relatively unnoticed or can occur at an
    alarming rate, causing serious loss of topsoil.
    Soil compaction, low organic matter, loss of soil structure, poor internal drainage
    and soil acidity problems are other serious soil degradation conditions that can

    accelerate the soil erosion process.


    Fig.2. 18 The erosive force of water from concentrated surface water runoff.

    Deposition is the geological process in which sediments, soil and rocks are
    added to a landform or land mass. Wind, ice, and water, as well as sediment
    flowing via gravity, transport previously eroded sediment, which, at the loss of
    enough kinetic energy in the fluid, is deposited, building up layers of sediment.
    2.4.4 Checking my progress
    The pictures A and B are of two geographical features. Look and carefully

    study the pictures to answer questions below.


    Fig.2. 18 Illustration of geographical features

    a. Interpret the images above and Use your observation to suggest names
    of the corresponding geographical features in the image above?
    b. Do you have such geographical features in your district or neighboring
    districts? Use your observation to explain clearly the two geographical
    features occurring in the image above?
    c. Explain the causes for each geographical feature occurring above?
    d. Can the geographical features identified above impact agriculture in
    our communities? Explain with clear facts to support your decision.
    e. What are moral and ethical issues associated with the geographical

    features given above?

    END UNIT ASSESSMENT 2
    A. Multiple choices questions
    For question 1 to 5, choose the letter of the best answer
    1. It is known that earth’s atmosphere has a series of layers, each with
    its own specific characteristics and properties? The following is the
    appropriate layer where we live.
    a. Thermosphere
    b. Troposphere
    c. Stratosphere
    d. Mesosphere
    2. Consider the following statements:
    I. The atmosphere of Earth protects life on Earth by absorbing
    ultraviolet solar radiation, warming the surface through
    greenhouse effect and reducing temperature extremes between
    day and night.
    II. X-rays and ultraviolet radiation from the Sun are absorbed in the
    thermosphere.
    III. The stratosphere extends from the top of the thermosphere to
    about 50 km above the ground.
    Of these statements:
    a. I, II, and III are correct.
    b. I, II and III are wrong
    c. I and II are correct but III is wrong
    d. I and III are wrong but II is correct
    3. Agrophysics is defined as
    a. The branch of science dealing with study of matter and energy
    and their mutual relation.
    b. The branch of science dealing with communication devices to
    measure and collect information about physical conditions in
    agricultural and natural environments.
    c. The branch of natural sciences dealing with the application of
    physics in agriculture and environment.
    d. None of these
    B. Structured Questions
    1. Write the missing word or words on the space before each number.
    For items (a)-(i)
    a. ___speeds up chemical weathering.
    b. Weathering happens ______ in hot, wet (humid) climates.
    c. Weathering occurs very slowly in _______ and ______ climates.
    e. In very ________ and ________ areas, there is little weathering.
    f. Most weathering occurs on ____________________of rocks and minerals
    g. The ________ surface area a rock has, the quicker it will weather.
    h. Some minerals resist weathering. _________________ is a mineral that
    weathers slowly.
    i. Rocks made up of minerals such as feldspar, ______, and iron, weather
    more quickly.
    2. If the statement is true, write true. If it is false, change the underlined word
    or words to make the statement true.
    a. Water vapor is very important in predicting weather.
    b. Temperature is a reason why atmosphere is more dense close to the
    earth’s surface.
    c. Agrophysics plays an important role in the limitation of hazards to
    agricultural objects and environment.
    d. Energy is transferred between the earth surface and planet in a variety
    of ways.
    e. As the temperature increases in the atmosphere, the minimum radiation
    occurs at short wavelengths.
    3. Write a sentence describing the relationship between each pair of terms.
    I. Gravity, atmosphere
    II. Temperature, rocks.
    4. Marry wants to make agrophysics journal. She says, “My journal will be
    focused on advances in sensors and communication devices to measure and
    collect information about physical conditions in agricultural and natural
    environments”. Evaluate Marry’s statement.
    5. With the help of two clear examples on each, explain clearly how

    temperature and water vapor impact agricultural activities using the table.

    6. Complete the chart below. If the left column is blank, give the correct
    term. If the right column is blank, give an example of economic activities

    taking place in the corresponding layer if possible.

    7. How do climate impact agricultural activities?
    8. Explain briefly the role of machines in agriculture in rapid development of
    the country towards suitable programs of transformation and modernization
    of agriculture?
    9. Knowing different stages of growing plants in our daily agriculture
    activities, explain clearly which stages mostly benefit the use of technology?
    10. Cracks in rocks widen as water in them freezes and thaws. How does this
    affect the surface of Earth?
    11. Name the four factors that can hasten or speed up the process of
    weathering.
    12. How is weathering different from erosion?
    13. How can increasing the surface area of rock hasten or speed up the
    process of weathering
    14. Human activities are responsible for enormous amounts of mechanical
    weathering, by digging or blasting into rock to build homes, roads, and
    subways or to quarry stone. Suggest measures that can be taken to minimize
    mechanical weathering caused by human activities?
    C. Essay type questions
    15. Design and conduct your own research into the influence of surfaces on
    temperature comparing earth surfaces that interest them (such as colored
    soils, dry and wet soils, grass, dry leaves, or different types of coverings
    such as plastic or aluminum foil). Compare the data with these new surfaces
    compared to the given surfaces (water, light soil, dark soil). Note that the
    data may not be comparable due to variations in experimental design, such

    as differences in light bulb temperature and height of the lamp.

  • UNIT 3 FOSSIL AND NON-FOSSIL FUEL AND POWER PRODUCTION

    Key unit competence: By the end of this chapter, I should be able to evaluate
    fossil and non-fossil fuel for power production.
    Unit Objectives:
    By the end of this unit I will be able to;
    • explain the concept of fossil and no-fossil fuels and their use in power
    production properly.
    • explain the differences between fossil and no-fossil fuels properly.
    • explain Nuclear fuel and nuclear fission and their use in energy
    production and associated dangers properly.
    • explain the environmental problems of fossil fuels and suggest their

    solution clearly.

    3.0 INTRODUCTORY ACTIVITY

    Fossil fuel is a source of conventional or non-renewable energy. There are
    many examples of fossil fuels which we use in our daily lives. In fact, most
    of the energy that we consume comes from fossil fuels. Coal, petroleum
    and natural gas are called fossil fuels. Millions of years ago, during the
    carboniferous age, due to the change in atmospheric conditions and other
    changes, the forests were destroyed and they were fossilized. With the action
    of bacteria and other microorganisms on the surface of the earth, these trees
    and other vegetations were decayed and disintegrated. Years after these
    trees were available in solid, liquid and gaseous state. The solid form is coal.

    It is the most widely used form of fossil fuel for domestic purposes.

    ACTIVITY 3.1: The Atmosphere
    Crossword puzzle: Fill the missing words in the crossword puzzle given
    below.
    Down
    1. __________ _________ refers to the rise in the world’s average
    temperature due to air pollution.
    2. _________ _______ are gases in the atmosphere that absorb and
    emit radiation, causing the greenhouse effect.
    3. ______________ is a mixture of smoke and fog in the atmosphere.
    4. ____________ ________is a non-renewable source of energy
    formed from the remains of dead plants and animals.
    Across
    5. ______ _____ is the reduction of the amount of ozone
    6. The water sources and the land are polluted by ______ ________

    when exhaust gases dissolve in the rain.

    ACTIVITY 3-2: Pollution
    Word splash

    The following are the key words we learn about air pollution.

    3.1. FOSSIL FUELS AND NON-FOSSIL FUELS
    3.1.1 Fossil Fuels

    Fossil fuels are hydrocarbons, primarily coal, fuel oil or natural gas, formed
    from the remains of dead plants and animals. In common dialogue, the term
    ‘fossil fuel’ also includes hydrocarbon-containing natural resources that are not

    derived from animal or plant sources.

    Fig. 3.1. Fossil fuels in nature

    Coal, oil and natural gas are called ‘fossil fuels’ because they have been formed
    from the fossilized remains of prehistoric plants and animals. Fossil fuels are
    non-renewable energy source since they take millions of years to form. They
    ultimately get their energy from the sun.
    Types of Fossil Fuels
    Coal
    Coal is a hard, black coloured rock-like substance formed when dead plants
    were subjected to extreme heat and pressure for millions of years. It is made up
    of carbon, hydrogen, oxygen, nitrogen and varying amounts of sulphur. There
    are two ways to mine coal: surface mining and underground mining.
    Natural Gas
    Natural gas is formed from the remains of tiny sea animals and plants that
    died millions of years ago. The gas then became trapped in layers of rock-like
    water in a wet sponge. Raw natural gas is a mixture of different gases. Its main
    ingredient is methane. The strange smell of natural gas (like rotten eggs) comes
    from a chemical added by the companies. It is called mercaptan. This is added
    to detect the gas leakage.
    Oil (Petroleum)
    Oil is formed from the remains of animals and plants that died millions of years
    ago. The organic material was then broken down into hydrogen and carbon
    atoms and a sponge-like rock was formed, full of oil.
    Oil cannot be used as it is when it is drawn from the ground. Oil refineries clean
    and separate the oil into various fuels and byproducts. The most important of
    these is gasoline.
    Fossil fuels are used to generate electrical energy in a series of energy

    transformations as shown in Fig.6.2.


    3.1.2 Non-fossil fuels
    Non-fossil fuels are alternative sources of energy or renewable sources of
    energy that do not rely on burning up limited supplies of coal, oil or natural
    gas. Examples of these fuels include: nuclear energy, wind or water generated
    energy and solar power. These tend to be renewable energy sources, or means
    of generating power that can be utilized indefinitely.
    Non-fossil fuels are considered to be extremely important for power creation.
    This is because they are usually renewable energy sources that could be tapped
    for hundreds of years and not run out. In addition, energy production using
    nonfossil-based fuels usually generates much less pollution than fossil-based
    energy sources.
    3.2 Storage and transportation of different types of fossil
    fuels
    3.2.1 Coal
    Types of coal
    • Peat
    • Lignite
    • Semi bituminous
    • Bituminous
    • Anthracite
    Means of transporting coal
    • Transportation by rail
    • Transportation by ropeways
    • Transportation by sea or river
    • Road transport
    • Transport by pipeline
    Coal storage
    Storage of coal is undesirable because it costs more as there is:
    • Risk of spontaneous combustion,
    • Weathering,
    • Possibility of loss and deterioration during storage,
    • Interest on capital cost of coal lying dormant,
    • Cost of protecting the stored coal from deterioration.
    Types of coal storage
    1. Dead storage:
    This storage supplies the coal to places where there is a shortage of coal in
    plant due to failure of normal supply of coal. This is a long-term storage and
    comprises 10% of annual consumption, so, it requires protection against
    weathering and spontaneous combustion.
    2. Living storage:
    It supplies coal to plant for day-to-day usage. The capacity of live storage is less
    than that of dead storage. It is usually stored in vertical cylindrical bunkers or
    coal basins or silos, e.g. coal is transferred to boiler grate. Bunkers are normally
    diamond-shaped cross-section storage areas made up of steel or reinforced
    concrete.
    Purpose of dead coal storage of coal
    • To prevent shutdown of power plant in case of failure of normal
    supplies of coal due to coal strike, failure of the transport system, etc.
    • To permit choice of purchase allowing management to take advantage
    of seasonal market conditions.
    Means of coal storage
    1. Storage in coal heaps
    It is required to:
    • Keep coal at low temperature (>70oC).
    • Prevention of air circulation from bottom of coal piles.
    • Proper drainage of rainy water to prevent weathering–drainage should
    not be rapid to prevent washing of coal.
    Hence, ground used for stocking should be dry and levelled for proper drainage.
    It should have concrete floor to prevent flow of air from bottom. Coal is piled up
    to a height of about 10 m to 12 m in layers of 15 cm to 30 cm.
    In dead storage, coal pile is sealed by asphalt, fine coal dust, bituminous or
    other coating materials.
    2. Underwater storage
    Possibility of slow oxidation and spontaneous combustion can be completely

    eliminated by storing coal under water.

    Fig. 3.3. Coal dead storage

    Site selection for coal dead storage
    • The storage should be free from standing water
    • If well drainage is not available, artificial drainage should be provided.
    • It should be free from all foreign materials like wood, paper rags, waste
    oil or materials having low ignition temperature.
    • Handling cost should be minimum.
    • Pile should build up in successive layers and be compact.
    • Pile should be dressed to prevent entry of rainy water.
    • Alternative drying and wetting should be avoided.
    • Stoker size coal should be oil treated to prevent absorption of water
    and oxygen.
    • Side of pile should not be steep.
    • Air may circulate freely through pile for proper ventilation to keep
    temperatures low.
    • Hot surfaces or boiler blow down or hot water or steam pipe and tanks
    should be kept far from coal storage
    • Hot bright days should be avoided.
    • There should be provision for temperature measurement at different
    points.
    • Conical piling should be avoided.
    • Fire fighting equipment should be easily available.
    Coal Transfer
    Equipments used in coal transfer are:
    A: Belt conveyor
    It can transfer large quantities of coal over large distance economically. It has

    low initial cost and ensures low power consumption.

    Fig. 3.4. Belt conveyor

    Advantages:

    • Economical, low power consumption

    • Large capacity

    • Rate of coal transfer rapidly change

    • Low maintenance cost

    Disadvantages

    • Not suitable for shorter distance and inclination > 200.

    • Not suitable for dust particles and slurry.

    B: Flight conveyor

    It is used when coal is discharged at different points in bins situated below the

    conveyor. All parts are made of steel and iron, so it can handle hot materials. It

    is totally enclosed, so dust of coal can get transferred. It can transfer coal at high

    inclination


    Fig. 3.5. Flight conveyor

    Advantages
    • It requires small head room.
    • Speed and material transfer rate can easily change.
    • It can handle hot materials also.
    Disadvantages
    • High wear and tear, so, it has short life.
    • High maintenance required.
    • Speed is limited up to 300 m/min due to abrasive action of material.
    • High power consumption per unit of material transfer.

    C: Screw conveyor


    Fig. 3.6. Screw conveyor

    • It is used for shorter distance.
    • It is totally enclosed from atmosphere.
    • Coal dust can also be transferred easily.
    • It is generally used in metering of coal.
    • Driving mechanism is attached at the end of the shaft.
    • Diameter: 15 cm to 50 cm.
    • Speed: 70 rpm to 120 rpm.
    • Capacity: 125 tones/h (max)
    Advantage
    • Cheap initial cost.
    • Simple and compact.
    • Dust tight.
    • It can transfer coal at high inclination also.
    • Most suitable for short distance.
    Disadvantages
    • High power consumption.
    • Length is limited up to 30 m.
    • High maintenance due to high wear and tear.
    D: Bucket elevator
    It is used for vertical lifts. Buckets are fixed on chain which moves on two wheels

    or sprockets. Buckets are loaded at bottom and discharged at top.

    Fig. 3.7. Bucket elevator

    E: Grab bucket elevator
    • It is used for lifting as well as transfer material.
    • It can be used with crane or tower.
    • Initial cost is high but operating cost is less.
    • It is used when another arrangement is not possible.
    • Bucket capacity: 2 to 3 m3
    • Distance: 60 m

    • Capacity: 100 tonnes/h.


    Fig. 3.8. Grab bucket elevator

    3.2.2 Transporting Natural Gas and Crude Oil
    Transporting natural gas and crude oil thousands of miles through pipelines is
    the safest method of transportation. The transportation system for natural gas
    consists of a complex network of pipelines, designed to transport natural gas
    from its origin to the areas of high natural gas demand quickly and efficiently.
    In general, pipelines can be classified in three categories depending on the
    purpose:
    Gathering pipelines
    These are smaller interconnected pipelines forming complex networks with
    the purpose of bringing crude oil or natural gas from several nearby wells to
    a treatment plant or processing facility. In this group, pipelines are usually
    short — a couple of hundred metres — and with small diameters. Also subsea
    pipelines for collecting product from deep water production platforms are

    considered gathering systems.


    Fig. 3.9. Gathering pipelines

    Transportation pipelines
    These are long pipes with large diameters, moving products (oil, gas, refined
    products) between cities, countries and even continents. These transportation
    networks include several compressor stations in gas lines or pump stations for

    crude and multi-products pipelines.


    Fig. 3.10. Transportation pipelines

    Distribution pipelines
    These are composed of several interconnected pipelines with small diameters,
    used to take the products to the final consumer. Feeder lines to distribute gas
    to homes and business downstream, and pipelines at terminals for distributing

    products to tanks and storage facilities, are included in this group.


    Fig. 3.11. Distribution pipelines

    3.3 Advantages and disadvantages of fossil fuels



    3.4 Energy production using fossil fuels
    A fossil-fuel power station is a power station which burns fossil fuels, such as
    coal, natural gas or petroleum to produce electricity. Central station fossil-fuel

    power plants are designed on a large scale for continuous operation.


    Fig. 3.12. Fossil fuel power plant

    There are two main cycles in a power plant; the steam cycle and the gas turbine
    cycle. The steam cycle relies on the Rankine cycle in which high pressure and
    high temperature steam raised in a boiler is expanded through a steam turbine
    that drives an electric generator. The generator then transforms mechanical
    energy into electrical energy which is distributed for local use.
    The steam gives up its heat of condensation to a heat sink, such as water from
    a river or a lake and the condensate can then be pumped back into the boiler
    to repeat the cycle. The heat taken up by the cooling water in the condenser is
    dissipated mostly through cooling towers into the atmosphere.
    3.5 Nuclear fuel and nuclear fission
    Nuclear fuel is any material that can be consumed to derive nuclear energy.
    The nuclear fuel can be made to undergo nuclear fission chain reactions in a
    nuclear reactor. The most common nuclear fuels are 235U (uranium 235) and
    239Pu (plutonium 239). Not all nuclear fuels are used in fission chain reactions.
    Nuclear fission is a process, by which a heavy nucleus splits into two or
    more simpler pieces. This process releases a lot of energy.
    When a neutron strikes an atom of uranium, the uranium nucleus splits into
    two lighter atoms and releases heat simultaneously. Fission of heavy elements
    is an exothermic reaction which can release large amounts of energy both as

    electromagnetic radiation and as kinetic energy of the fragments.


    Fig. 3.13. Fission of Uranium 235

    A chain reaction refers to a process in which neutrons released in fission
    produce an additional fission in at least one further nucleus. This nucleus in
    turn produces neutrons, and the process continues. If the process is controlled
    it is used for nuclear power or if uncontrolled it is used for nuclear weapons.
    Fig.3.13 illustrates a chain reaction of uranium 235.

    The equation of reaction is:

    3.6 Controlled fission (power production)
    Of the three neutrons, liberated during a fission reaction, only one triggers a
    new reaction and the others are simply captured. The system is in equilibrium.
    One fission reaction leads to one new fission reaction, which leads to one

    more, and so on. This is known as controlled fission.

    Fig. 3.14. Controlled fission reaction

    In a nuclear power station, the uranium is first formed into pellets and then into
    long rods. The uranium rods are kept cool by submerging them in water. When
    they are removed from the water, a nuclear reaction takes place causing heat
    production. The amount of heat required is controlled by raising and lowering
    the rods. If more heat is required, the rods are raised further out of the water
    and if less heat is needed, they are lowered further into it.
    3.7 Uncontrolled fission (nuclear weapons)
    A fission reaction which is allowed to proceed without any moderation (by
    removal of neutrons) is called an uncontrolled fission reaction. Here more and
    more neutrons are given out and cause more fission reactions, thus, releasing
    large amounts of energy. An uncontrolled fission reaction is used for nuclear

    bombs.

    Using the energy released from the nuclear fission of uranium-235, an explosive
    device can be made by simply positioning two masses of U-235 so that they can
    be forced together quickly enough to form a critical mass and result in a rapid,
    uncontrolled fission chain reaction.
    This is not an easy task to accomplish. First, you must obtain enough uranium
    which is highly enriched to over 90% U-235, since natural uranium is only
    0.7% U-235. This enrichment is an exceptionally difficult task, a fact that has
    helped control the proliferation of nuclear weapons. Once the required mass is
    obtained, it must be kept in two or more pieces until the moment of detonation.
    Then the pieces must be forced together quickly and in such a geometry that
    the generation time for fission is extremely short. This leads to an almost
    instantaneous build up of the chain reaction, creating a powerful explosion
    before the pieces can fly apart. Two hemispheres which are explosively forced
    into contact, can produce a bomb, such as the one detonated at Hiroshima in

    1945.


    Fig. 3.15. Nuclear atomic bomb of Uranium 235.

    3.8 Impacts of nuclear weapons
    There are five immediate destructive effects from a nuclear explosion:
    1. The initial radiation, mainly gamma rays;
    2. An electromagnetic pulse, which in a high altitude explosion can knock out
    electrical equipment over a very large area;
    3. A thermal pulse, which consists of bright light (even many miles away) and
    intense heat equal to that at the centre of the sun);
    4. A blast wave that can flatten buildings; and
    5. Radioactive fallout, mainly in dirt and debris that is sucked up into the
    mushroom cloud and then falls to earth.
    There are three long-term effects of a nuclear explosion:
    1. Delayed radioactive fallout, which gradually fall over months and even years
    to the ground, ofen in rain;
    2. A change in the climate (possibly by lowering of the earth’s temperature
    over the whole hemisphere which could ruin agricultural crops and cause
    widespread famine);
    3. A partial destruction of the ozone layer, which protects the earth from
    the sun’s ultraviolent rays. If ozone layer is depleted, unprotected Caucasians
    would get an incapacitating sunburn within 10 minutes, and people would
    suffer a type of snow blindness from the rays which, if repeated, would lead
    to permanent blindness. Many animals would suffer the same fate.
    3.9 Energy transformations in a nuclear power station
    In a nuclear power plant, Nuclear Steam Supply System (NSSS) consists of a
    nuclear reactor and all of the components necessary to produce high pressure

    steam, which will be used to turn the turbine for the electrical generator.


    Fig. 3.16. Nuclear power plant

    The nuclear reactor contains some radioactive isotopes like uranium which
    undergo fission reaction when bombarded with some neutrons and a large
    amount of heat energy is evolved. This heat energy converts water into steam,
    which is piped to the turbine. In the turbine, the steam passes through the
    blades, which spins the electrical generator, resulting in a flow of electricity.
    After leaving the turbine, the steam is converted (condensed) back into water
    in the condenser. The water is then pumped back to the nuclear reactor to be
    reheated and converted back into steam.
    3.10 Problems associated with the production of nuclear
    power
    • The problem of radioactive waste is still unsolved. The waste
    from nuclear energy is extremely dangerous and it has to be carefully
    looked after for several thousand years (10,000 years according to
    United States Environmental Protection Agency standards).
    High risks: Despite a generally high security standard, accidents
    can still happen. It is technically impossible to build a plant with
    100% security. A small probability of failure will always last. The
    consequences of an accident would be absolutely devastating both for
    human beings and the nature. The more nuclear power plants (and
    nuclear waste storage shelters) are built, the higher is the probability
    of a disastrous failure somewhere in the world.
    • Nuclear power plants as well as nuclear waste could be preferred
    targets for terrorist attacks. Such a terrorist act would have
    catastrophic effects for the whole world.
    • During the operation of nuclear power plants, radioactive waste is
    produced, which, in turn, can be used for the production of nuclear
    weapons. In addition, the same is used to design nuclear power plants
    can to a certain extent be used to build nuclear weapons (nuclear
    proliferation).
    • The energy source for nuclear energy is Uranium. Uranium is a
    scarce resource; its supply is estimated to last only for the next 30 to
    60 years depending on the actual demand.
    • The timeframe needed for formalities, planning and building of a new
    nuclear power generation plant, is in the range of 20 to 30 years in the
    western democracies. In other words, it is an illusion to build new
    nuclear power plants in a short time.
    3.11 Environmental problems of fossil fuels
    Climate Change/Global Warming and Greenhouse Effect
    The earth’s atmosphere allows a lot of sunlight to reach the earth’s surface
    but reflects much of that light back into space. Some gases trap more sunlight,
    therefore, less light is reflected back into space. These gases are called
    Greenhouse Gases, because the effect is like being in a plant glasshouse,
    or in a car with the windows wound up. The result is a gradual increase in
    the earth’s temperature or Global Warming. The major greenhouse gases are
    carbon dioxide, methane, nitrous oxide and chlorofluorocarbons (CFCs).
    The main man made causes are thought to be carbon dioxide and methane from
    factory, power station and car emissions, the waste products of respiration, the
    mining of fossil fuels and the breakdown of plant matter in swamps. The longterm
    effects may include melting of glaciers and a rise in sea level and a global
    change in climate and type of vegetation.
    ‘Hole’ in the Ozone Layer
    Ozone is a gas in the earth’s upper atmosphere whose chemical formula is O3.
    Ozone acts to block out much of the sun’s ultraviolet radiation which causes
    skin cancer and contributes to the fluctuations of global climatic conditions
    that affect the environment. Above Antarctica, there is a thinner layer of ozone
    caused by the destruction of ozone gas by emissions of chlorofluorocarbons
    and hydrochlorofluorocarbons which are propellants in pressure-pack spray
    cans and refrigerants in refrigerators and air-conditioning units.
    Acid Rain
    When gases, such as sulphur dioxide and nitrogen oxides react with water in
    the atmosphere to form sulphuric acid and nitric acid, they form an acidic ‘rain’
    which can destroy vegetation. Some of these gases are from natural sources,
    such as lightning, decomposing plants and volcanoes. However, much of these
    gases are the result of emissions from cars, power stations, smelters and
    factories.
    Air Pollution
    Air pollution is the release of excessive amounts of harmful gases (e.g. methane,
    carbon dioxide, sulphur dioxide, nitrogen oxides) as well as particles (e.g.
    dust of tyre, rubber, lead from car exhausts) into the atmosphere. To reduce
    emissions, the Australian government has legislated that all new cars should
    use unleaded petrol and have catalytic converters fitted to the exhausts.
    Water Pollution
    1. Sewage is the household waste water. Many detergents contain phosphates
    which act as plant fertilisers. When these phosphates and the sewerage
    reach rivers, they help water plants to grow in abundance, reducing the
    dissolved oxygen in the river water. The result is death of aquatic animals
    due to suffocation by the algal blooms. This harmful effect is called
    eutrophication. Eutrophication is also caused by excessive use of fertilizers
    in agricultural fields and subsequent surface run-off.
    2. Biodegradable detergents are more environment-friendly because they are
    readily broken down to harmless substances by decomposing bacteria.
    3. Suspended solids in water, such as silt reduce the amount of light that
    reaches the depths of the water in lakes and rivers. This reduces the ability
    of aquatic plants to photosynthesise and reduce the plant and animal life.
    Turbidity is the measure of ‘cloudiness’ or the depth to which light can
    reach in water.
    Introduced Species
    They are species of plants or animals that have migrated or been brought to
    Australia. Many fit into the natural ecosystems and are kept in control by natural
    predators and parasites. However, some become pests as they are well-adapted
    to that environment, readily obtain nutrients and lack of natural predators or
    parasites. Examples include rabbits, foxes, carp and prickly pear cactus plant.
    Biological Control
    It is an environment-friendly method to control these pests by the introduction
    of species-specific, living organisms to control their numbers. Successful
    examples include the myxoma virus and the calici virus for rabbits, and the
    cactoblastis moth feeding on the prickly pear. Unsuccessful examples include
    the introduction of the cane toad to reduce the numbers of natural cane beetles.
    Biological Magnification
    It is the accumulation in body tissues of certain chemicals, such as DDT,
    pesticides and mercury. The higher it moves along the food chain, the greater
    is the accumulation, sometimes to such toxic levels, which causes birth defects
    and even death.
    Soil Salinity
    Soil salinity has increased greatly since the widespread logging of trees by
    farmers. Deep tree roots normally draw water from the underground water
    table. However, when logging of trees occurs, the water table rises close to
    the surface bringing with it, salt from rocks. This makes the soil salty so that
    vegetation cannot grow effectively. The result is loss of vegetation and erosion.
    Population Explosion
    It is the rapid increase in population in developing countries causing famine,
    and also in developed countries causing more demand for energy and with
    that, it increases pollution and destruction of the environment.
    ACTIVITY3-3: Sources of Pollution
    Aim: the aim of this activity is to find out the causes of pollution.
    Procedure: analyse the figure below and answer the questions that

    follow

    Fig. 3.17. Effects of poorly deposited nuclear wastes.

    a. Outline some sources of water and air pollution shown on the figure.
    b. Explain how each of the cause in (a) affect the environment.
    c. Give and explain any other sources of air and/ or water pollution you
    know.
    d. Explain how air and water pollutions can be reduced.
    ACTIVITY 3-4: Wate Pollution
    Aim
    : to investigate the effect of water contamination
    Source: internet and textbooks or journals.
    Background Information
    1. Scientists have studied the influence of chlorine on organic
    materials in water supplies. Some of the chlorine reacts with this
    organic material to form chloroform and other chlorine-containing
    chemicals. Research has shown that some chlorine-containing
    chemicals can increase the risk of cancer.
    2. Working with your group, find out more about the benefits and
    costs of using chlorine in the water supply. Have each member of
    your group research information on one of the following:
    a. The risk to health of not treating water supplies with chlorine
    b. The risk to health of using chlorine in water treatment
    c. Alternatives to using chlorine for water treatment
    d. Scientific research underway on chlorine use
    e. What (if anything) is used to treat your local water supply
    Support Your Opinion
    3. When you have finished your research, share your information
    with your group. Design a presentation to summarize your group’s
    findings. Be prepared to share your group’s findings with the rest
    of the class.
    4. Do you think that the amount of chlorine in our water should be
    increased at certain times of the year? Give reasons to support your

    opinion

    3.12 Safety issues and risks associated
    with nuclear power
    3.12.1 Nuclear Meltdown
    A nuclear meltdown is an informal term for a severe nuclear reactor accident

    that results in core damage from overheating.

    Fig. 3.18. Reactor meltdowns at Fukushima Daiichi.

    A nuclear meltdown occurs when a nuclear power plant system or component
    fails so the reactor core becomes overheat and melts. Usually, this occurs due to
    the lack of coolant that decreases the temperature of the reactor. The commonly
    used coolant is water but sometimes a liquid metal, which is circulated past the
    reactor core to absorb the heat, is also used. In another case, a sudden power
    surge that exceeds the coolant’s cooling capabilities causes an extreme increase
    in temperature which leads to a meltdown. A meltdown releases the core’s
    highly radioactive and toxic elements into the atmosphere and environment.
    The causes of a meltdown occur due to:
    A: A loss of pressure control
    The loss of pressure control of the confined coolant may be caused by the failure
    of the pump or having resistance or blockage within the pipes. This causes the
    coolant to cease flow or insufficient flow rate to the reactor; thus, the heat
    transfer efficiency decreases.
    B: A loss of coolant
    A physical loss of coolant, due to leakage or insufficient provision, causes a
    deficit of coolant to decrease the heat of the reactor. A physical loss of coolant
    can be caused by leakages. In some cases, the loss of pressure control and
    the loss of coolant are similar because of the systematic failure of the coolant
    system.
    C: An uncontrolled power excursion
    A sudden power surge in the reactor is a sudden increase in reactor reactivity.
    It is caused by an uncontrolled power excursion due to the failure of the
    moderator or the control that slows down the neutron during chain reaction.
    A sudden power surge will create a high and abrupt increase of the reactor’s
    temperature, and will continue to increase due to system failure. Hence, the
    uncontrollable increase of the reactor’s temperature will ultimately lead to a
    meltdown.
    3.12.2 Nuclear (Radioactive) Wastes
    Nuclear wastes are radioactive materials that are produced after the nuclear
    reaction. Nuclear reactors produce high-level radioactive (having high levels
    of radioactivity per mass or volume) and low-level (having low levels of
    radioactivity) wastes. The wastes must be isolated from human contact for a

    very long time in order to prevent radiation.

    Fig. 3.19. High level waste being stored in underground repository.

    The ‘high-level wastes’ will be converted to a rock-like form and placed in a
    natural habitat of rocks, deep underground. The ‘low-level wastes’, on the other
    hand, will be buried in shallow depths (typically 20 feet) in soil.
    A number of incidents have occurred when radioactive material was disposed
    improperly, where the shielding during transport was defective, or when the
    waste was simply abandoned or even stolen from a waste store.
    The principal risks associated with nuclear power arise from health effects
    of radiation, which can be caused due to contact with nuclear wastes. This
    radiation consists of sub-atomic particles travelling at or near the velocity of
    light (186,000 miles per second). They can penetrate deep inside the human
    body where they can damage biological cells and thereby initiate a cancer. If

    they strike sex cells, they can cause genetic diseases in progeny

    END UNIT ASSESSMENT 3
    1. Why should solar energy be harnessed to take care of our electric
    power needs?
    2. How do we confirm that the ‘greenhouse effect’ is real?
    3. How does acid rain destroy forests and fish?
    4. Is it possible to eliminate the air pollution from coal burning?
    5. Radioactivity can harm us by radiating from sources outside our
    bodies, by being taken in with food or water or by being inhaled
    into our lungs. But we consider only one of these pathways. Why is
    it so?
    6. Cancers from radiation may take up to 50 years to develop, and
    genetic effects may not show up for a hundred years or more. How,
    then, can we say that there will be essentially no health effects from
    the Three Mile Island accident?
    7. Air pollution may kill people now, but radiation induces genetic
    effects that will damage future generations. How can we justify our
    enjoying the benefits of nuclear energy while future generations
    bear the suffering from it?
    8. Can the genetic effects of low-level radiation destroy the human
    race?
    9. Isn’t the artificial radioactivity created by the nuclear industry,
    more dangerous than the natural radiation which has always been
    present?
    10. Can radiation exposure to parents cause children to be born with two
    heads or other such deformities?
    11. Can a reactor explode like a nuclear bomb?
    12. If reactors are so safe, why don’t home owners’ insurance policies cover
    reactor accidents? Does this mean that insurance companies have no
    confidence in them?
    13. How is radioactive waste disposed off?
    14. How long will the radioactive waste be hazardous?
    15. How will we get rid of reactors when their useful life is over?
    Fossil fuels are hydrocarbons, primarily coal, fuel oil or natural gas, formed
    from the remains of dead plants and animals.
    Types of Fossil Fuels
    • Coal
    • Natural Gas
    • Oil (Petroleum)
    Types of coal storage
    • Dead storage
    • Living storage
    Means of coal storage
    • Storage in coal heaps
    • Underwater storage
    Energy production using fossil fuels
    A fossil-fuel power station is a power station which burns fossil fuel, such as
    coal, natural gas or petroleum to produce electricity.
    Nuclear fuel and nuclear fission
    Nuclear fuel is any material that can be consumed to derive nuclear energy.
    Controlled fission (power production)
    When a fission reaction leads to a new fission reaction, which leads to another
    one and so on, it is called controlled fission. The amount of heat required is
    controlled by raising and lowering the rods in the reactor.
    Uncontrolled fission (nuclear weapons)
    A fission reaction whereby the reaction is allowed to proceed without any
    moderation (by removal of neutrons) is called an uncontrolled fission reaction.
    An uncontrolled fission reaction is used for nuclear bombs.
    Problems associated with the production of nuclear power
    • problem of radioactive waste.
    • high risks.
    • targets for terrorist attacks.
    • nuclear weapons.
    • uranium is a scarce resource.
    • illusion to build new nuclear power plants.
    Environmental problems of fossil fuels
    Climate Change / Global Warming and Greenhouse Effect
    The earth’s atmosphere allows a lot of sunlight to reach the earth’s surface, but
    reflects much of that light back into space.
    The result is a gradual increase in the earth’s temperature or Global Warming.
    ‘Hole’ in the Ozone Layer
    Ozone acts to block out much of the sun’s ultraviolet radiation which causes
    skin cancer and contributes to the fluctuations of global climatic conditions
    that affect the environment.
    Acid Rain
    When gases, such as sulphur dioxide and nitrogen oxides react with water in
    the atmosphere to form sulphuric acid and nitric acid, they form an acidic ‘rain’
    which can destroy vegetation.
    Air Pollution
    Air pollution is the release into the atmosphere of excessive amounts of harmful
    gases as well as particles.
    Other environmental problems of fossil fuels include:
    • Biological Control
    • Biological Magnification
    • Introduced Species
    • Soil Salinity

    • Population Explosion

  • UNIT 4:ATOMIC NUCLEI AND RADIOACTIVE DECAY

    Fig.4. 1: Sign of radiation precaution

    Key unit competence: Analyse atomic nuclei and radioactivity decay
    My goals
    • Define atomic mass and atomic number
    • Identify the constituents of a nucleus
    • Explain Einstein’s mass-energy relation.
    • Define nuclear fusion and fission.
    • Analyze determinations of a mass of nuclei by using Bainbridge mass
    spectrometer.
    • Derive the relationship between decay constant and half-life.
    • Determine the stability of a nuclei.
    • Describe properties of different radiations.
    • Describe creation of artificial isotopes.
    • Identify the application of radioactivity in life.
    • Plot a graph of binding energy against nucleon and explain its features.
    • Calculate the decay rate of unstable isotopes.
    • Appreciate the safety precautions to be taken when handling radioactive
    materials.
    • Appreciate that the nucleus of an atom and quantum system has discrete

    energy levels.

    INTRODUCTORY ACTIVITY


    In different places like industries, hospitals, and other sensitive places, there
    are different posts that caution someone about dangerous substances one
    may encounter if care is not taken. Among the reasons why these places bare
    such instruction is because of chemicals and radiations that are used in such
    places which may be harmful if not handled with care.
    1. Discuss some of the safety signs you have ever seen in any hospitals or
    industry if you have ever visited one.
    2. Why do you think there is a need to put those signs in such places?
    3. It is believed that there are some of diseases that are treated using
    radioactive substances. Can you state some of the radiations used to
    treat some diseases.
    4. There are natural men made radioactive substances. All of these are
    used for different purposes. What are some of negative effects of these
    radiations to (i) man , (ii) environment
    5. Some countries like Iran are affected by these radiations. Imagine you
    were a resident of that country, what would you do to protect yourself

    from such effects of radioactive substances.

    4.1 ATOMIC NUCLEI-NUCLIDE
    4.1.1 Standard representation of the atomic nucleus

    ACTIVITY 4.1: Investigating the stable and unstable nicleus


    Fig.4. 2 The standard representation of an atom nucleus
    Observe the Fig.4.1 above of an atom and answer to the questions that
    follow:
    1. What do numbers A and Z stand for?
    2. Describe the relation between the two numbers and their meanings.
    3. When do we say that an atom is stable or unstable?
    4. Explain clearly the meaning of isotopes. Give an example of isotopes

    you know.

    A nucleus is composed of two types of particles: protons and neutrons. The
    only exception is the ordinary hydrogen nucleus, which is a single proton. We
    describe the atomic nucleus by the number of protons and neutrons it contains,
    using the following quantities:
    a. The atomic number or the number of protons Z in the nucleus (sometimes
    called the charge number).
    b. The neutron number or the number of neutrons N in the nucleus.
    c. The mass number or the number of nucleons in the nucleus,
                                          A = Z + N.                         (4.01)
    In representing nuclei, it is convenient to use the symbol AZ
    to show how many
    protons and neutrons are present in the nucleus. X represents the chemical
    symbol of the element. For example, 5626 Fe nucleus has mass number 56 and
    atomic number 26. It therefore, contains 26 protons and 30 neutrons.
    When no confusion is likely to arise, we omit the subscript Z because the
    chemical symbol can always be used to determine Z. Therefore, 5626 Fe is the same
    as 56 Fe and can also be expressed as “iron-56.” Each type of atom that contains

    a unique combination of protons and neutrons is called nuclide.

    4.1.2 Classification
    Depending on the combinations of protons and neutrons in the nucleus,
    nuclides can be classified in the following 3 categories:
    a. Isotopes: These are nuclei of a particular element that contain the same
    number of protons but different numbers of neutrons. Most elements
    have a few stable isotopes and several unstable, radioactive isotopes.

    Example of isotopes:

    Therefore, the chemical properties of different isotopes of an element are
    identical but they will often have great differences in nuclear stability. For
    stable isotopes of light elements, the number of protons will be almost equal to
    the number of neutrons. Physical properties of different isotopes of the same
    element are different and therefore they cannot be separated by chemical
    methods i.e. only physics methods such as the centrifugation method can be
    used to separate different isotopes of an element.
    b. Isobars: these are nuclei which have the same mass number but different

    number of protons Z or neutrons N.

    c. Isotones: these are nuclei in which the number of neutrons is the same

    but the mass number A and the atomic number Z differ

    4.1.3 Units and dimensions in nuclear physics
    The standard SI units used to measure length, mass, energy etc. are too large
    to use conveniently on an atomic scale. Instead appropriate units are chosen.
    • The length: The unit of length in nuclear physics is the femtometer.
    1 fm =10−15 m
    This unit is called Fermi in the honor of the Italian Americano physicists who

    did a lot of pioneering work in nuclear physics.

    • The mass: The unit used to measure the mass of an atom is called the
    atomic mass unit, abbreviated “amu or u” and is defined as a1⁄12 the
    mass of an atom of carbon-12. Since mass in grams of one carbon-12

    atom is its atomic mass (12) divided by Avogadro’s number gives.

    • Nuclear masses can be specified in unified atomic mass units (u).
    On this scale:
    • A neutral 126 C atom is given the exact value 12.000000 u.
    • A neutron then has a measured mass of 1.008665 u,
    • A proton 1.007276 u,
    • A neutral hydrogen 11H
     atom (proton plus electron) 1.007825 u
    Energy: the SI unit used for energy that is Joule is too large. In nuclear physics
    the appropriate unit used for energy is an electronvolt (eV). An electron volt
    (eV) isdefined as the energy transferred to a free electron when it is accelerated
    trough a potential difference of one volt. This means that
    1eV =1.6022×10−19 C×1V =1.6022×10−19 J
    It is also a common practice in nuclear physics to quote the rest mass energy
    calculated using ,
                                                      E = mc2                                                                        (4.02)
    Since the mass of a proton is mp =1.67262  ×10 −27kg =1.007276 u, then 1 u is equal to

    This is equivalent to energy in MeV of   

    • The time: the time involved in nuclear phenomena is of the order of
    10-20s to million or billion years.
    • Nuclear radius: various types of scattering experiments suggest that
    nuclei are roughly spherical and appear to have the same density. The

    data are summarized in the expression called Fermi model.

    Where r0  =12 fm  =1.2 × 10−15 m  and A is the mass number of the nucleus
    The assumption of a constant density leads to the estimate of the mass density

    which is obtained by considering.

    This high density can explain why ordinary particles cannot go through the
    nucleus as highlighted by Rutherford experiments. The same density was only
    observed in neutron stars. The nuclear mass can be determined using a mass
    spectrometer.
    4.1.4 Working principle a mass spectrometer
    The figure below highlights the working principle of a typical mass spectrometer
    used to separate charges of different masses. It can be used to differentiate

    isotopes of a certain element.

    Fig.4. 3: Bainbridge mass spectrometer

    Ions are formed in ionization chamber and accelerated towards the cathode.
    The beam passes through the cathode and is focused by the collimating slits S1
    and S2. The beam is then passed through a velocity selector in which electric
    and magnetic fields are applied perpendicular to each other. The ion moves in
    straight line path for which both the forces acting on it are equal
                                 qE = qvB
    The velocity of ion which passes un-deflected through the velocity selector is

    then given by   

    The ions then reach the vacuum chamber where they are affected by the
    magnetic field  alone and then move in circular paths; the lighter ions
    having the larger path radius. If the mass of an ion is m, its charge q and its

    velocity v then

    The radius of the path in the deflection chamber is directly proportional to the
    mass of the ion. The detection is done by photographic plate when the ions fall
    on it. The fig. 4.5 shows the recorded mass spectrum for a gas containing three
    isotopes. Note the wider line for the mass m1, showing its relatively greater

    abundance.

    4.1.5 Checking my progress



    4.2 MASS DEFECT AND BINDING ENERGY
    4.2.1 Mass defect
    ACTIVITY 5.2: Select the words in the following puzzle
    Observe the puzzle below:
    1. Discover 8 different words related to particle Physics hidden in the
    puzzle below, and write them in your notebook.

    2. Use them to formulate a meaningful sentence


    3. Complete the sentences below using the words you discovered in
    the puzzle
    a. An …….is the SI unit of energy
    c. The ………..of nucleons is greater than the mass of a nucleus.
    d. The atom releases ………when its nucleus is formed from its
    constituent particles
    e. The binding energy per nucleon gives an indication of the …………
    of the nucleus.
    f. The surprising suggestion that energy and mass are equivalent
    was made by ……in 1905.
    4. Discuss and explain the meaning of the following expression as used in
    physics
    a. Mass defect c. Electronvolt

    b. Biding energy d. Stable nuclides

    The nucleus is composed of protons that are positively charged and neutrons
    that are neutral. The question is what is holding these particles together in
    this tiny space?
    Experiences have demonstrated that the mass of a nucleus as a whole is always
    less than the sum of the individual masses of protons and neutrons composing
    that nucleus.
    The difference between the two measurements is called mass defect Δm . For a

    nucleus  

    4.2.2 Einstein mass-energy relation
    In 1905, while developing his special theory of relativity, Einstein made the
    surprising suggestion that energy and mass are equivalent. He predicted that if
    the energy of a body changes by an amount of energy E, its mass changes by an
    amount m given by the equation
                                                    E = mc2                                                                                  (4.09)
    Where c is the speed of light and m mass of a body
    Everyday examples of energy gain are much too small to produce detectable
    changes of mass.
    4.2.3 Binding energy
    The mass of a nucleus is less than the combined mass of its protons and
    neutrons (nucleons). The missing mass is called the mass defect. This observed
    mass defect represent a certain amount of energy in the nucleus known as the
    binding energy b E and calculated using the Einstein formula as:
                                                    ΔE = Δmc                                        (4.10)
    where c is the speed of light and Δm the mass defect.

    The binding energy for a nucleus containing Z protons and N neutrons is defined as

    The binding energy is the energy released when a nucleus is formed from its
    constituent particles or the energy required to break up (to split) the nucleus
    into protons and neutrons. Protons and electrons are held together in the
    nucleus of an atom by the strong nuclear force. So if we imagine splitting a
    nucleus up into its separate protons and neutrons, it would require energy,
    because we would need to overcome the strong nuclear force.
    4.2.4 Binding energy per nucleon and stability
    Instead of looking at the total binding energy of a nucleus, it is often more useful
    to consider the binding energy per nucleon. This is the total biding energy

    divided by the total number of nucleons.

    A plot of binding energy per nucleon Eb/A as a function of mass number A for

    various stable nuclei is shown on Fig. 5.6.

    Fig.4. 5: The graph of binding energy per nucleon of the known elements (Giancoli D. C., 2005)

    The nuclear binding energy per nucleon for light element increases with the
    mass number until a certain maximum is reached at around A = 56 and then
    after it almost saturate. The fact that there is a peak in the binding energy per
    nucleon curve means that either the breaking of heavier nucleus (fission) or
    the combination of lighter nuclei (fusion) will yield the product nuclei with
    greater binding energy per nucleon and therefore more stable.
    As an example if a nucleus like is 23892U split into two fragments of nearly equal
    masses, the two fragments will have higher binding energy per nucleon than
    the original. The excess energy is released as useful energy and this process
    called fission is the basis of electricity production in a nucleus plant.
    If two light elements combine their nuclei in one nucleus, the formed nucleus

    will have a greater binding energy per nucleon than the originals.


    This process is called nuclear fusion and can only take place at a very high
    temperature. It is the source of energy in the sun and other stars. The fusion is
    more energetic than the fission.
    The binding energy per nucleon therefore gives an indication of the stability
    of the nucleus. A high binding energy per nucleon indicates a high degree of

    stability – it would require a lot of energy to take these nucleons apart.

    4.2.5 Checking my Progress


    4.3 RADIOACTIVITY AND NUCLEAR STABILITY
    ACTIVITY 4.3: Investigating radioactivity
    During the World War II, its final stage was marked by the atomic bombing
    on Nagasaki and Hiroshima towns in Japan (Fig.5.6). Observe the image and

    read the text provided below before answering the following questions.


    Fig.4. 6: The atomic bomb in Nagasaki (Japan in 1945)

    In August 1945, after four years of world war, united States B-29 bomber,
    dropped the atomic bomb over the cities of Hiroshima on August 6th 1945.
    70.000 people died in 9 seconds, and the city of Hiroshima was leveled. 3 days
    after as second bomb was dropped in Nagasaki, Japan with the same devastating
    results. The bombing killed over 129.000 people.
    The bomb released cataclysmic load of energy. The ones who were close enough
    to see the blast lost their eyes. It was the last thing they ever saw. The bright
    light of what the blinded them. The black of their eyes, the retina, melted away.
    The radiation received by the body is equivalent today’s thousands of x-rays.
    The human body can’t absorb unlimited radiation. It falls apart because the
    cells are dying of radiation poisoning, if the radiation is intense enough, it looks
    like a urn. Layers of the skin begin to fall off. The body vital functioning began
    to slow down until it stops.
    1. Describe and discuss the phenomena happening on two images.
    2. From the text, show that the atomic bomb of Hiroshima was very harmful
    to human body.
    3. What are the types of radiations should be there?
    4. Stable isotopes do not emit radiations. What is the name of materials which
    emit radiations? Describe them.
    5. What are the possible main radioisotopes used to produce energy in figure
    above?
    6. Which processes are used to generate such heavy energy? Describe any one
    of your choice
    Radioactivity is one of the dynamic properties of nuclei, in this process the
    system makes a transition from a high energy state to a low energy by emitting
    α and β-particles or γ-rays. This process happens naturally and is not affected by
    any external agent such as pressure, temperature or electric and magnetic fields.
    The α-particles are Helium nuclei and can be stopped by a piece of paper while
    β-particles are either electron or positron. There are high energetic particles
    and can pass through one cm thick aluminum sheet. γ-rays are electromagnetic
    radiations and can be stopped by several inches of lead.
    4.3.1 Radioactive decay of a single parent
    Nucleus decay is a random process and the rate of disintegration is proportional
    to the number of available radioactive nuclides. Let us analyses the simple case
    where the first daughter nuclide is stable. Suppose that at time t, there are N
    radioactive nuclide and dN is the number of nuclide disintegrating within a
    time dt. As the rate of disintegration is proportional to the number of nuclides
    present in the radioactive substance, we get

    where λ, the proportionality constant, is called the radioactive constant.
    This constant depends on the nature of the radioactive substance. The negative
    sign shows that an increase in disintegration rate will decrease the number of
    radioactive nuclides which are present. From this we can establish the formula

    of radioactive decay:


    where it assumed that the initial number of radioactive nuclide is equal to N0.


    Fig.4. 7: Illustration of the radioactive decay law

    If we consider the activity A of a radioactive sample which is the number of
    decay events in a unit time we obtain a similar expression for the radioactive

    decay law but expressed in terms of activity of the radioactive substance:


    where A0 is the initial activity of the radioactive source. Another parameter
    useful in characterizing nuclear decay is the half-life T1⁄2 .
    The half-life of a radioactive substance is the time interval during which half

    of a given number of radioactive nuclei decay. Therefore the half time period is


    Finally,one shows that the mean-life of a nuclide or the average life period of a

    nuclide is related to the radioactive constant by


    In general, after n half-lives, the number of un-decayed radioactive nuclei

    remaining is 



    4.3.2 Characteristics of radioactive substances
    Radioactive substances (nuclides) present one or more of the following features
    • The atom of radioactive elements are continually decaying into simpler
    atoms as a result of emitting radiation
    • The radiations from radioactive elements produce bright flashes of
    light when they strike certain compounds. The compound fluoresce.
    For example, rays from radium cause zinc sulphide to give off light in
    the dark. For this reason, a mixture of radium and zinc sulphide is used
    to make luminous paints.
    • They cause ionization of air molecules. The radiations from radioactive
    substances knock out electrons from molecules of air. This leaves the
    gas molecules with a positive charge.
    • Radiations from radioactive substances can penetrate the heavy black
    wrapping around a photographic film. When the film is developed, it
    appears black where the radiations struck the film.
    • Radiations from radioactive substances can destroy the germinating
    power of plants seeds, kill bacteria or burn or kill animals and plants.
    Radiations can also kill cancers.
    A. Properties of emitted radiations

    Some of their properties are summarized and shown in the table below:


    Table 4. 3 Properties of different types of radiations

    a. Alpha decay ( 42He )
    If one element changes into another by alpha decay, the process is called
    transmutation. For alpha emission to occur, the mass of the parent must be
    greater than the combined mass of the daughter and the alpha particle.
    In the decay process, this excess of mass is converted into energy of other forms
    and appears in the form of kinetic energy of both the daughter nucleus and
    the alpha particle. Most of kinetic energy is carried away by the alpha particle
    because it is much less massive than the daughter nucleus. The momentum is
    conserved in this process.
    The isotope whose natural radioactive decay involves the emission of alpha
    particles usually have a relative atomic mass greater than 210 (Ar>210). They
    have too much mass to be stable and give out alpha particles to form smaller

    and more stable atoms.

    b. Beta decay
    The isotopes whose radioactive decay involves the emission of beta particles
    often have a relative atomic mass less than 210 (Ar < 210). Beta particles are
    usually emitted from heavier nuclei that have too many neutrons compared
    with the number of protons.
    I. Negative β-decay

    In this process of negative β-decay an electron and an antineutrino are emitted.

    The emitted electron results from the following reaction where a neutron
    changes into a proton and an electron is emitted from the nucleus as a beta

    particle:

    The conservation of charges and mass number is maintained. The daughter

    nuclide may be in an excited state and will become stable after emitting a γ-ray.

    II. Positive β-decay

    In this process the positron and the neutrino are emitted.

    This positive decay is different from an electron capture which takes place
    when an electron that is close to the nucleus recombines with a proton in the

    nucleus producing a neutron and a neutrino:

    The equation of decay of the electron capture is:

    The daughter nuclide is seem to be the same as that we could have been
    produced if a positron has been emitted. The rearrangement of the remaining
    Z-1electrons will lead to emission of characteristic x-ray of the daughter
    nucleus. In few case both positron and electron capture may happen.
    C. Gamma decay (Y)
    Very often a nucleus that undergoes radioactive decay is left in an excited
    energy state. The nucleus can then undergo a second decay to a lower energy
    state by emitting one or more photons. Unlike α and β decay, γ decay results
    in the production of photons that have zero mass and no electric charge. The
    photons, emitted in such process, are called gamma rays and they have very
    high energy.
    If an atom of a material Y emits a γ ray (γ photon), then the nuclear reaction can

    be represented symbolically as  

    Gamma emission does not result in any change in either Z or A.
    Notes:
    • A transmutation does not occur in gamma decay. When an alpha
    particles and beta particles are emitted, gamma rays are often emitted
    at the same time. When a radioisotope emits gamma rays, it become
    more stable because it loses energy.
    • In both alpha and beta decay, the new element formed is called the

    daughter isotope.

    • Gamma rays are like X-rays. Typical gamma rays are of a higher
    frequency and thus higher energy than X-rays.
    • Deviations of alpha, beta and gamma radiations due to electric field and
    magnetic field ( See Fig.4.9). It can be seen unlike gamma-rays, alpha
    and -particles are affected by the presence of electric and magnetic
    fields since these particles are charged. Gamma-rays are not affected

    by these fields.


    Fig.4. 8: Deviation of radiation particles in an electric field

    4.3.3 Nuclear fission and Fusion
    a. Nuclear fission
    Heavy unstable nuclides can be broken up to produce energy in a process
    called nuclear fission. When uranium decays naturally, alpha and beta particles
    are emitted. However, when uranium-235 is bombarded by neutrons it forms
    uranium-236. Uranium-236 is unstable and breaks down, splitting into two
    large particles and emitting three neutrons. The fission of 235U by thermal

    neutrons can be represented by the reaction


    where 236U∗ is an intermediate excited state that lasts for approximately10-12s
    before splitting into medium-mass nuclei X and Y, and these are called fission

    fragments.

    Fig.4. 9: Fission diagram illustration

    When the exact masses of the final products are added together, the sum is
    found to be appreciably less than the exact masses of the uranium-235 and the
    original neutron. This difference in mass Δm appears as energy given by
    Δm = Δmc2
    Another important point arises! The three neutrons released may collide with
    other nuclides and split them also resulting in cascade reactions. In this way,
    chain reactions occur and as a result, the quantity of energy released can be
    very large. A few kilogram of uranium can produce as much heat energy as
    thousands of tons of coal.
    Advantages and disadvantages of nuclear fission
    The nuclear fission produces a huge amount of energy. This energy can
    be released in a controlled manner in nuclear power station and be used in
    driving steam turbines that produce electric power. However, when produced
    in uncontrolled manner it will result in the fabrication of atomic bomb that may
    release a large amount of heat energy and damaging radiations. The emitted
    radiations have both short term and long term effect on the living things.
    b. Nuclear fusion
    When lighter nuclides merge together in a process called fusion, energy is

    produced and mass is lost. For example: 


    These reactions occur in the core of a star and are responsible for the outpouring
    of energy from the star.
    The sum of the exact masses of the helium atom is less than the sum of exact
    masses of the four hydrogen atoms. This lost mass is released as energy. It is
    thought that the sun’s energy is produced by nuclear fusion.
    4.3.4 Radiation detectors
    ACTIVITY 4.4: Smoke detector bellow
    Observe the diagram of a smoke detector bellow then answer to the

    questions that follow:

    Fig.4. 10: illustration diagram of a smoke detector

    1. Name the components labeled A, B, C and D on the smoke detector
    above?
    2. What is meant by smoke detector?
    3. Describe a functioning of a smoke detector.
    4. Design an inventory of other radiation detectors you know
    Experiments in Nuclear and Particle Physics depend upon the detection of
    primary radiation/particle and that of the product particles if any. The detection
    is made possible by the interaction of nuclear radiation with atomic electrons
    directly or indirectly.
    a. Classification of radiation detectors
    There are a variety of other radioactive detectors that we may conveniently

    classify into two classes: Electrical and Optical detectors.



    Table4. 1 Classification of radiation detectors

    b. Working principle of an ionization chamber
    Conventionally, the term “ionization chamber” is used exclusively to describe
    those detectors which collect all the charges created by direct ionization within
    the gas through the application of an electric field. Ionization chamber is filled
    with inert gases at low pressure. In the chamber there are two electrodes,
    namely, the cathode and the anode which are maintained at a high potential

    difference as shown on the figure below


    Fig,4.11: visualization of ion chamber operation

    When radiation enters the chamber, it ionizes the gas atoms creating negative
    and positive charges. The negative charges or electrons are attracted by the
    anode while positive ions are attracted by the cathode; this produces the current
    in the outside circuit depending on the strength and the type of radiation. The
    current produced is quite small and dc amplified electrometers are used to

    measure such small currents.

    4.3.5 Checking my progress
    In the following exercises (1 to 4), choose the best answer and explain your
    choice
    1. Which of the following is an electron?
    a. Neutrino c. Photon
    b. Gamma particle d. Beta particle
    2..Which of the following most accurately describe radioactive decay?
    a. Molecules spontaneously break apart to produce energy
    b. Atoms spontaneously break apart to produce energy beta decay, alpha
    decay and positron emission are all forms of radioactive decay. Energy is
    released because the atoms are converted to a more stable energy
    c. Protons and neutrons spontaneously break apart to produce energy
    d. Electrons spontaneously break apart to produce energy
    3. Which of the following is true concerning the ratio neutrons to protons in
    stable atoms?
    a. The ratio for all stable atoms is 1:1.
    b. The ratio for small stable atoms is 1:1, and the ratio for large stable atom is
    greater than 1:1. As atomic weight goes up, the ratio of neutrons to protons
    for stable atoms increases up to as much as 1.8:1 ratio.
    c. The ratio for large stable atom is 1:1, and the ratio for small stable atoms
    is greater than 1:1.
    d. There is no correlation between the stability of the atom and its neutron
    to proton ratio.
    4. Polonium-218 undergoes one alpha decay and two beta decays to make
    a. Polonium-214 c. Bismuth-214
    b. Plomb-214 d. Plomb-210
    5. a) Compare (i) the charge possessed by alpha, beta and gamma radiations
    (ii) The penetrating power of these radiations
    6. a.What is meant by the term (i) radioactive decay? (ii) Half-life of a radioactive
    substance?
    b. A 32 g sample of radioactive material was reduced to 2 g in 96 days. What is its
    half-life? How much of it will remain after another 96 days?
    7. 212Be Decays to 208Th by α-emission in 34% of the disintegration and to212Ra
    by β-emission in 66% of the disintegration. If the total half value period is 60.5
    minutes, find the decay constants for alpha and beta and the total emission.
    8. If a radioactive material initially contains 3.0milligrams of Uranium234U , how
    much it will contain after 150,000 years? What will be its activity at the end of

    this time?

    4.4 APPLICATION OF RADIOACTIVITY

    ACTIVITY 5.5: Use of nuclear energy to generate electricity


    Fig.4. 12: Nuclear power plant functioning mechanism diagram.

    Many people disagree to the use of nuclear power to generate our
    electricity, even though the safety record of nuclear industry is extremely
    good. Observe clearly the image diagram of the nuclear power plant
    (Fig.4.12) and answer to the questions that follow
    1. Why do you think people disagree to the use of nuclear power
    station?
    2. What are the main parts of the power plant station observed in
    Fig.5.12?
    3. Analyze and explain the steps of energy transformation from reactor
    to generator
    4. Write a brief explanation on the advantages and disadvantages of
    using nuclear energy as a source of electricity if any.
    5. Use internet and your library or any other resources to find out
    about the other application of radionuclides in our daily life
    People would not have fear of radiations when controlled in certain manner.
    Radioisotopes and nuclear power process have been used and produced
    improvement in various sectors. These includes: consumer products, food and
    agriculture, industry, medicine and scientific research, transport, water
    resources and the environment. The following are some descriptive examples
    among others.
    4.4.1 Industry
    Different materials we use at home are manufactured in industry and made of
    different radioactive materials. The dosage of use of radioactive substance is
    thus controlled so that they are not harmful to human body.
    Gamma radiation and beta radiation from radio-isotopes can be used to
    monitor the level of the material inside the container. The penetrating power
    of gamma rays is used to detect hidden flow in metal castings. Beta rays are
    used to measure the thickness of various flat objects (the mass absorbed by the
    object is proportional to its thickness).
    In the textile industries, irradiation with beta radiations fixes various chemicals
    onto cotton fibers. This produces for instance permanent press clothing. Again,
    radioactive materials can be used as tracers to investigate the flow of liquids in

    chemical factories.

    Fig.4. 13 Testing the level of a liquid in a container using radiations

    If there is a sudden decrease in the amount of radiation reaching the detector,
    which will happen when the container is full, then this can be used as a signal
    to switch off the flow of substance into the container. A similar method is used
    to monitor the thickness of sheets of plastic, metal and paper in production.
    4.4.2 Tracer studies
    Tracer techniques can be used to track where substances go to and where leaks
    may have occurred. Leaks in gas pipes or oil pipes can be detected by using this
    technique. Tracer techniques are also used in medicine to treat thyroid glands
    which can be underactive or over active. The activity of the thyroid gland can
    be monitored by the patient being injected with or asked to drink radioactive
    iodine. The radioactivity in the vicinity of the thyroid gland is then checked to
    see how much of the radioactive iodine has settled in the area around the gland.
    4.4.3 Nuclear power stations
    Nuclear power stations control a large amounts of energy released when
    Uranium-235undergoes nuclear fission. The energy released by this controlled
    chain reaction, is then used to produce electricity.
    4.4.4 Nuclear fusion
    In nuclear fusion, the nuclei of elements with a very low atomic number are fused
    together to make heavier elements. When this takes place, it is accompanied by
    a very large release of energy. In the sun, hydrogen nuclei are fusing together
    all the time to make helium nuclei. This is also the process by which a hydrogen
    bomb works.
    4.4.5 Medicine
    ACTIVITY 4.6: Radionuclides in Medicine

    Observe the figure below and suggest answers to the question below

    Fig.4. 14: A gamma camera assembly. The photons emitted in the patients are detected
    by the photomultiplier tubes. A computer monitor displays the image computed from

    the photomultiplier signals.

    1. Who is this person (a man or a woman)?
    2. Where is he?
    3. What does the image on the right represent?
    4. What do you think the patient is suffering from?
    5. Using the knowledge acquired in optics, what kind of light
    propagation observed there?
    6. Does the imaging use reflection or refraction? Why?

    7. What should be the name of radiation being used in this imaging?

    Nuclear medicine has revolved treatment of different disease of the century. It
    consists on the use of nuclear properties of radioactive substances in diagnosis,
    therapy and research to evaluate metabolic, physiologic and pathologic
    conditions of human body. Today, nuclear medicine is currently used in the
    diagnosis, treatment and prevention of many serious sicknesses.
    Cancer cells are more easily killed by radiation than healthy cells. In medicine,
    penetrating gamma rays of cobalt-60 sources are used for this purpose. Other
    cancers such as skin cancers are treated by less penetrating beta radiation from
    strontium-90 source. Surgical instruments can also be sterilized using gamma
    radiation.
    4.4.6 Food preservation
    The preservation of food uses gamma rays is spreading worldwide. Treating
    food with gamma rays can:
    • Slow down the ripening of some fruits and the sprouting of potatoes.
    In both cases, this helps storage and increases the half-life of the food.
    • Kill highly dangerous micro-organisms such as salmonella
    • Kill micro-organisms that spoil food
    4.4.7 Radiocarbon dating
    There are three isotopes of carbon: carbon-12, carbon-13 and carbon-14. The
    isotope carbon-14 is radioactive and has half-life of 5760 years. To estimate
    the age of a biological sample, radiocarbon146C is used as a radioactive
    nuclide. Nucleus decay is independent of the physical or chemical condition
    imposed on the elements. This can be used to measure the ages of biological
    samples by considering the ratio of 146Cwhich is radioactive and 126C in dead
    species. Radioactive carbon is produced when cosmic rays interact with

    air atoms to produce neutrons and these neutrons interact with nitrogen

    The half-life period of 146Cis equal to 5760 years. The carbon reacts with oxygen
    to produce CO2 and plants combine this CO2 with water in the process of
    photosynthesis to manufacture their food. Therefore plants and animals are
    radioactive. When plants or animals die, the 146Cin them keeps on decaying
    without any new intake. The ratio of 146C and 126C will therefore be different in
    dead and leaving plants and animals. The age of the dead plant or animal can be

    estimated by measuring this ratio.

    4.4.8 Agricultural uses
    In agriculture, radionuclides are used as tracers for studying plants, insect
    and animals. For example, phosphorus-32 can be added to plant fertilizer.
    Phosphorus is absorbed by plants and its distribution can be measured.
    Radiation has been used in South American to detect and control the screw
    worm fly pest. A large number of the male of the species were exposed to
    gamma radiation. When the males were released back into the wild and mated
    with wild females, sterile eggs resulted and no new flies were born.
    The points of photosynthesis in a leaf are revealed by growing it in air containing
    carbon-14. The presence of this radioactive nuclide in the leaf is the revealed
    by putting the leaf onto a photographic plate and letting it take its own picture.

    4.4.9 Checking my progress

    1. Suggest different uses of radionuclides in (i) Medicine (ii) food and
    agriculture
    2. In our daily life, we are exposed to radiations of different types mainly
    in materials we use.
    a. Make an inventory of all of the devices in your home that may have
    (contain) a radioactive substance.
    b. What is the origin of these radiations in the materials highlighted
    above?
    c. Explain the purpose of radioactive material in the device.
    d. Then make research to find out how the objects shown in Fig.5.15 use

    radiation in their manufacture.


    Fig.4. 15

    4.5 HAZARDS AND SAFETY PRECAUTIONS OF WHEN
    HANDLING RADIATIONS

    ACTIVITY 4.7: Investigating the safety in a place with radiations


    Fig.4. 16: Radiation effects on human body according to the exposure.

    The image above (Fig.4.16) shows different side effects of radiation on
    human body according to the exposure time taken. With reference to
    section 4.3 and activity 4.3, answer to the following questions:
    1. What are the dangers of radiations you may observe?
    2. Analyze measures should be taken for radiation users?
    4.5.1 Dangers of radioactivity
    • Both beta particles and gamma rays can pass easily in the skin and can
    easily destroy or even kill cells, causing illness.
    • They can cause mutations in a cell’s DNA, which means that it cannot
    reproduce properly, which may lead to diseases such as cancer.
    • Alpha particles cannot pass through the skin. However, they are
    extremely dangerous when they get inside your body. This can happen
    if you inhale radioactive material.
    4.5.2 Safety precautions when Handling Radiations
    The precautions taken by workers who deal with radioactive materials are:
    • Wearing protective suits
    • Wearing radiation level badges
    • Checking the radiation level regularly
    • Using thick lead-walled containers for transporting radioactive
    materials
    • Using remote control equipment from behind thick glass or lead walls
    to handle radioactive material
    • They should be held with forceps and never touched with hands.
    • No eating, drinking or smoking where radioactive materials are in use
    • Wash your hands thoroughly after exposure of to any radioactive
    materials
    • Any cuts in the body should be covered before using radioactive sources
    • Arrange the source during experiments such that the radiation window
    points away from your body

    • There are ten golden rules for working safely with radioactivity.

    END UNIT ASSESSMENT 4
    A. Multiple choice questions
    Instructions: Write number 1 to 5 in your notebook. Beside each
    number, write the letter corresponding to the best choice
    1. Radionuclides
    a. Are those nuclides having more neutrons than protons
    b. May emit X-rays.
    c. Decay exponentially
    d. May be produced in a cyclotron
    2. Concerning Compton Effect:
    a. There is interaction between a photon and a free electron.
    b. The larger the angle through which the photon is scatted, the
    more energy it loses.
    c. The wavelength change produced depends upon the
    scattering material.
    d. High energy radiation is scatted more than lower energy
    radiations.
    e. The amount of scattering that occurs depends on the electron
    density of the scattering material.
    3. Classical physics offered a satisfactory explanation for
    a. The diffraction of electrons by crystals
    b. The deflection of charged particles in an electric field
    c. The intensity spectrum of black body radiation
    d. The photoelectric effect
    e. Matter waves
    4. When investigating β decay, the neutrino was postulated to explain
    a. Conservation of the number of nucleons
    b. Counteracting the ionizing effect of radiation
    c. Conservation of energy and momentum
    d. The production of antiparticles
    e. The energy to carry away the β particles.
    5. Gamma radiations differ from α and β emissions in that
    a. It consist in photons rather than particles having nonzero
    rest mass
    b. It has almost no penetrating ability
    c. Energy is not conserved in the nuclear decays producing it
    d. Momentum is not conserved in the nuclear decays producing it
    e. It is not produced in the nucleus
    6. The process represented by the nuclear equation is 
    a. Annihilation c. β decay e. γ decay
    b. α decay d. pair production
    7. Write number (i) to (iii) in your note book. Indicate beside each number
    whether the corresponding statement is true (T) or false (F). If it is false,
    write a corrected version.
    I. An alpha particle is also called a hydrogen nucleus
    II. The neutrino was suggested to resolve the problem of conserving
    energy and momentum in β decay.
    III. The amount of energy released in a particular α or β decay is found
    by determining the mass difference between the products and the
    parent. A mass-energy equivalence calculation then gives the energy.
    IV. The average biding energy per nucleon decreases with the increasing
    atomic mass number
    8. A radioactive source emits radiations alpha, beta and gamma a shown
    below:

    Fig.4. 17 Absorption of radiation
    The main radiation(s) in the beam at X and Y are

    9. The energy released by the nuclear bomb that destroyed Hiroshima was
    equivalent to 12.4 kilotons of TNT. This is equivalent to 9.1 × 1026 MeV.
    The mass that was Converted into energy in this explosion was (Convert

    MeV in Joules, use E=mc2)

    10. In the decay scheme (Conserve charge and electron lepton number) the

    blanks should contain

    11. Complete the following sentences by using a word, number and an
    equation where necessary

    a. The half-life in years of the decay represented by the graph in fig.4.18

    Fig.4. 18 Half life carve

    b. When an animal or plant dies, no more _______________is taken in and
    that which is present undergoes radioactive decay. If we measure the
    amount of carbon-14 left, it is possible to determine the________ of the
    sample.
    c. If an atom of material Y emits a gamma ray (gamma photon), then the

    nuclear reaction can be represented symbolically as_________________

    B. Structured questions
    12. Prepare a table summarizing the three types of radioactive emission.
    Classify each type under the following headings: Type of Emission,
    Mass, Charge, penetrating Power and Ionization Ability.
    13. Copy the following table in your notebook and answer the questions

    that follow

    14. Give the value of x and y in each of the following equations

    15. Give the value of x and y in each of the reaction classify each as α , β ,

    or γ decay

    16. The half-life of carbon14 is 5730 years the mass of certain sample of
    this isotope is800 μg . Graph the activity for the first 5 half-lives.
    17. Beams of a, b- and g radiation of approximately the same energy pass

    through electric and magnetic fields as shown below.

    a. Show the path taken by each particle in the two fields. Why do
    they follow these paths?
    b. Which particle is the most penetrating? Explain your answer.
    c. Which has the highest ionizing power?
    d. How are β + and electrons different?
    e. How are x-rays, y rays and photons different?
    18. We are exposed to radiation all the time, indoors and outdoors. This is
    called background radiation.
    a. Give two examples of sources of this background radiation.
    b. Which organ generally receives the most background radiation, and
    why?
    c. There is some concern at the moment that pilots and flight attendants
    may have significantly higher exposures to radiation than the normal
    exposure rates for the general public.
    d. Why do pilots have a higher exposure to radiation than most other
    people?
    19. Nuclei can decay by emitting particles which can change the energy, mass
    and charge of the nucleus.
    a. How is α decay possible when the α particle must pass an energy
    barrier which is greater than the energy of the particle? Describe the
    process involved.
    b. If isotope A emits α particles with greater energy than isotope B (of
    the same element), which will have the longer half-life?
    c. How can a nucleus change its charge without emitting a charged

    particle?

    C. Question of research
    21. Using the information in radioactivity and making an internet search
    or/ and using other sources of information, consolidate your skills in
    other hazardous materials you may meet in your area. Then complete

    the table below (not exhaustive):

    Table 4. 7 Precaution signs

  • UNIT 5 APPLICATIONS OF OPTICAL FIBER IN TELECOMMUNICATION SYSTEMS.

    Key unit competence: Differentiate optical fiber transmission and other
    transmitting systems.
    My goals
    • Explain the functioning of optical fiber
    • Explain attenuation in optical fiber
    • Identify and explain the components of optical fiber system
    • Solve problem related to attenuation giving answers in decibels
    • Describe telecommunication system
    • Describe functions of amplifiers in optical fiber transmission
    • Distinguish optical fiber and other telecommunication systems
    INTRODUCTORY ACTIVITY
    Investigating the use of optical fiber in RWANDA
    Rwanda plans to connect three million people to the World Wide Web as
    part of the “Internet for All” project. The project is a World Economic Forum
    initiative that aims to connect 25 million new Internet users in Kenya,
    Uganda, South Sudan and Rwanda by 2019.
    This goal will partly be achieved by addressing the challenges of affordability,
    digital skills gap, lack of local content and limited infrastructure, which are
    hindering growth in the use of Internet across the region (http://www.

    threastafrican.co.ke, 2017)

    Fig.5. 1: The installation and use of optical fiber in Rwanda

    1. Observe the images A, B and C (Fig.5.1) and describe what you can see.
    2. What are the uses of optical fiber in transmission of signals?
    3. How do optical fibers function? In which field?
    4. Discuss other applications of optical fibers.
    5.1 PRINCIPLES OF OPERATIONS OF OPTICAL FIBERS

    ACTIVITY 5.1: Total internal reflection in optical fiber.


    Fig.5. 2: The total internal reflection in the optical fiber
    Given the illustration above (Fig.5.2), one can see different rays inside

    the optical fiber.

    As the angle of incidence in the core increases, as the angle of refraction
    increases more until it becomes right angle at a certain value of incidence
    angle called critical angle. Discuss:
    1. What do you understand by the term critical angle?
    2. What causes the total internal reflection?
    3. Discuss different fields where total internal reflection can be useful.
    5.1.1 Definition
    An optical fiber (fiber optics) is a medium for carrying information from one
    point to another in the form of light. It uses a flexible, transparent fiber made
    by drawing glass or plastic and has a diameter slightly thicker than that of
    a human hair. They are arranged in bundles called optical cables and can be
    used to transmit signals over long distances. Fiber optics continues to be used
    in more and more applications due to its inherent advantages over copper

    conductors.

    Fig.5. 3: An optical cable and a bundle of optical fibers

    An optical fiber is made of 3 concentric layers:
    • Core: This central region of the optical fiber is made of silica or doped
    silica. It is the light transmitting region of the fiber.
    • Cladding: This is the first layer around the core. It is also made of
    silica, but not with the same composition as the core. This creates an
    optical waveguide which confines the light in the core by total internal
    reflection at the core-cladding interface.
    • Coating: The coating is the first non-optical layer around the cladding.
    The coating typically consists of one or more layers of polymer that

    protect the silica structure against physical or environmental damage.

    Fig.5. 4: the structure of optical fiber

    The light is guided down the core of the fiber by the optical cladding which has
    a lower refractive index. Remember that the refractive index is the ratio of the
    velocity of light in a vacuum to its velocity in a specified medium. Then light is
    trapped in the core through total internal reflection. The other outer parts that
    are the strength member and the outer jacket, serve as protectors.
    Connecting two optical fibers is done by fusion splicing or mechanical splicing.
    It requires special skills and interconnection technology due to the microscopic
    precision required to align the fiber cores.
    5.1.2 Refractive index of light
    When light falls at the interface (boundary) of two media, it is partially reflected
    and partially refracted. As it passes from one medium to another it changes its

    direction.


    Fig.5. 5: Refraction of light from air to water and water to air for comparison.

    The change in its direction is associated with the change in velocity. The ratio of
    the speed of light in the vacuum c (or air) and that of light in a certain medium

    v is called the absolute refractive index n.


    5.1.3 Total internal reflection
    When light passes from one a medium of higher index of refraction into a medium
    of lower refractive index the light bends away from the normal as indicated on
    Fig.6.6. A weak internally reflected ray is also formed and its intensity increases

    as the incident angle increases.

    Fig.5. 6: Illustration of total internal reflection

    Increasing the angle of incidence increases the angle of refraction and at a
    particular incidence, the angle of refraction reaches the 90°. This particular
    incident angle is called the critical angle θc. As the incident angle exceeds the
    critical angle, the incident beam reflects on the interface between the 2 media
    and return in the first medium. This effect is called total internal reflection.

    For any two media, using Snell’s law the critical angle is calculated using the

    expression 
    where n1 and n2 are respectively the refractive indices of the first and second
    media.

    θc increases when approaches n1  .

    EXAMPLE 5.1

    Applying the above relation to the critical ray at a glass-air boundary we

    have where index of glass is ng =1.50.

    Answer 

    A beam of light is propagating through diamond, n = 2.42 and strikes a
    diamond-air interface at an angle of incidence of 28°.
    Will part of the beam enter the air or will the beam be totally refracted
    at the interface?
    Repeat part (a) assuming that diamond is surrounded by water, n = 1.33
    Answer: 
    Since 28° is greater thanθC  , total internal reflection will occur, there is no

    refraction. 

    Since 28° is less than θC some light will undergo refraction into the water.

    Application:

    An optical fiber is basically made of 2 types of glass put together in a concentric
    arrangement so the middle is hollow. The inner circle of glass also called the
    Core consists of a glass of higher refractive index than the outside layer as

    indicated on fig.5.4.

    Fig.5. 7: Total internal reflection in optical fiber as the angle of incidence θ is greater than the

    critical angle.

    The outer layer of glass, which is also known as the optical cladding, does not
    carry light but is essential to maintain the critical angle of the inner glass. The
    underlying main physics concept behind the functioning of an optical fiber is a
    phenomenon known as total internal reflection.
    Any light entering the fiber will meet the cladding at an angle greater than
    the critical angle. If light meets the inner surface of the cladding or the core -
    cladding interface at greater than or equal to critical angle then total internal
    reflection (TIR) occurs. So all the energy in the ray of light is reflected back into
    the core and none escapes into the cladding. The ray then crosses to the other
    side of the core and, because the fiber is more or less straight, the ray will meet
    the cladding on the other side at an angle which again causes the total internal
    reflection. The ray is then reflected back across the core again and again until it
    reaches the end of the optical fiber.
    Maximum angle of incidence
    The maximum angle of incidence in air for which all the light is total reflected
    at the core-cladding is given by:  

    EXAMPLE 6.2

    1. An optical fibre consists of an inner material (the fiber) with refractive
    index nf and an outer material of lower refractive index nc, known as

    cladding, as in Fig. 6.6 below.

                                                     Fig.5. 6

    a. What is the purpose of cladding?

    b. Show that the maximum acceptance angle θmax is given

    c. Discuss two main fiber loss mechanisms.

    Answer

    The purpose of the cladding is to improve the transmission efficiency

    of the optical fibre. If cladding is not used then the signal is attenuated

    dramatically.

    Let a ray be incident at an angle θ , Fig.6.6, the angle of refraction at P

    being θp Let C be the critical angle at Q, interface of core and cladding

    (in this case θCmax  )

    Refraction from air to core: 

    This shows that there is a maximum angle of acceptance cone outside of
    which entering rays will not be totally reflected within the fiber. For the
    largest acceptance cone, it is desirable to choose the index of refraction of the
    cladding to be as small as possible. This is achieved if there is no cladding at
    all. However, this leads to other problems associated with the loss of intensity.
    d. The transmission is reduced due to multiple reflections and the absorption
    of the fibre core material due to impurities.
    2. A step-index fiber 0.01 cm in diameter has a core index of 1.53 and a
    cladding index of 1.39. See Fig.5.7. Such clad fibers are used frequently in

    applications involving communication, sensing, and imaging.

                                                                                                 Fig.5. 7

    What is the maximum acceptance angle θmfor a cone of light rays incident on
    the fiber face such that the refracted ray in the core of the fiber is incident on

    the cladding at the critical angle?


    5.1.4 Checking my progress
    1. Operation of optical fiber is based on:
    a. Total internal reflection
    b. Total internal refraction
    c. Snell’s law
    d. Einstein’s theory of reality
    e. None of the above
    2. When a beam of light passes through an optical fiber
    a. Rays are continually reflected at the outside(cladding) of the fiber
    b. Some of the rays are refracted from the core to the cladding
    c. The bright beam coming out of the fiber is due to the high refractive
    index of the core
    d. The bright beam coming out of the fiber is due to the total internal
    reflection at the core-cladding interface
    e. All the rays of light entering the fiber are totally reflected even at very
    f. small angles of incidence 
    3. A laser is used for sending a signal along a mono mode fiber because
    a. The light produced is faster than from any other source of light
    b. The laser has a very narrow band of wavelengths
    c. The core has a low refractive index to laser light
    d. The signal is clearer if the cladding has a high refractive index
    e. The electrical signal can be transferred quickly using a laser
    4. Given that the refractive indices of air and water are 1 and 1,33,
    respectively, find the critical angle.
    5. The frequency of a ray of light is 6.0x1014 Hz and the speed of light in air is
    3x108 m/s. the refractive index of the glass is 1.5.
    a. Explain the meaning of refracting index
    b. A ray of light has an angle of incidence of 30° on a block of quartz and an
    angle of refraction of 20°. What is the index of refraction of the quartz?
    6. A beam of light passes from water into polyethylene (n = 1.5). If θi = 57.5°,
    what is the angle of refraction?
    7.
    a. What is the critical angle when light is going from a diamond (n= 2.42)
    to air?
    b. Using the answer to (a), what happens when:
    I. The angle of incidence is less than that angle?

    II. The angle of incidence is more than that angle

    5.2 TYPES OF OPTICAL FIBERS
    ACTIVITY 5.2: Investigating the types of optical fiber.
    Use search internet and discuss different types of optical fiber. Then,
    differentiate them according to their respective uses.
    There are three main types of Optical Fibers: Monomode (or single
    mode), Multimode and special purpose optical fibers.
    5.2.1 Monomode fibers
    Those are Fibers that support a single mode and are called single-mode
    fibers (SMF). Single-mode fibers are used for most communication links longer

    than 1 000 m.

    Fig.5. 8: Structure of monomode or single-mode optical fiber

    In the monomode fiber, the core is only about 8 μm in diameter, and only
    the straight through transmission path is possible, i.e. one mode. This type,
    although difficulty and expensive to make, is being used increasingly. For short
    distances and low bit-rates, multimode fibers are quite satisfactory. Following
    the emergence of single-mode fibers as a viable communication medium in
    1983, they quickly became the dominant and the most widely used
    fiber type within Telecommunications. Major reasons for this situation are
    as follows:
    1. They exhibit the greatest transmission bandwidths and the lowest losses of
    the fiber transmission media.
    2. They have a superior transmission quality over other fiber types
    because of the absence of modal noise.
    3. They offer a substantial upgrade capability (i.e. future proofing) for future
    wide- bandwidth services using either faster optical transmitters or
    receivers or advanced transmission techniques (e.g. coherent technology,).
    4. They are compatible with the developing integrated optics technology.
    5. The above reasons 1 to 4 provide confidence that the installation of singlemode
    fiber will provide a transmission medium which will have adequate
    performance such that it will not require replacement over its anticipated
    lifetime of more than 20 years. (John, 2009)
    5.2.2 Multimode fiers
    In multimode fier, light travels through the fier following diffrent light paths
    called “modes” as indicated on Fig.5.9. Those are fiers that support many
    propagation paths. A multi-mode optical fier has a larger core of about 50 μm,
    allowing less precise, cheaper transmitters and receivers to connect to it as

    well as cheaper connectors

    Fig.5. 9 Multimode optical fiber

    The propagation of light through a multimode optical fiber is shown on Fg.
    5.9. However, a multi-mode fiber introduces multimode distortion, which
    often limits the bandwidth and length of the link. Furthermore, because of its
    higher dopant content, multi-mode fibers are usually expensive and exhibit
    higher attenuation.
    There are two types of multi-mode optical fibers: multimode step-index and

    multimode graded index (see Fig.5.10)


    Fig.5. 10: Step index and graded index multimode optical fibers illustration.

    In step-index multimode type, the core has the relatively large
    diameter of 50μm and the refractive index changes suddenly at the
    cladding. The wide core allows the infrared to travel by several paths
    or modes. Paths that cross the core more often are longer, and signals
    in those modes take longer to travel along the fiber. Arrival times at the
    receiver are therefore different for radiation of the same pulse, 30ns
    km-1, being a typical difference. The pulse is said to suffer dispersion,
    it means that it is spread out.
    • In the graded index multimode type, the refractive index of the glass
    varies continuously from a higher value at the center of the fiber to a
    low value at the outside, so making the boundary between core and
    the cladding indistinct. Radiation following a longer path, travel faster
    on average, since the speed of light is inversely proportional to the
    refractive index. The arrival times for different modes are the about
    the same (to within 1ns km-1) and all arrive more or less together at the
    receiving end. Dispersion is thereby much reduced.
    5.2.3 Special-purpose optical fiber
    Some special-purpose optical fiber is constructed with a non-cylindrical
    core and/or cladding layer, usually with an elliptical or rectangular crosssection.
    These include: polarization-maintaining fiber and fiber designed to
    suppress whispering gallery mode propagation.
    • Polarization-maintaining fiber is a unique type of fiber that is
    commonly used in fiber optic sensors due to its ability to maintain the
    polarization of the light inserted into it.
    • Photonic-crystal fiber is made with a regular pattern of index
    variation. It is often in the form of cylindrical holes that run along the
    length of the fiber. Such fiber uses diffraction effects in addition to total
    internal reflection, to confine light to the fiber’s core.
    5.2.4 Checking my progress
    1. Fiber optics is best known for its application in long-distance
    telecommunications.
    a. True
    b. False
    2. Choose the basic types of optical fiber:
    a. Single-mode e. Multi-mode
    b. X-mode f. A and C
    c. Microwave-mode g. B and D
    d. Graded-index mode h. A and E
    3. Single-mode fiber has the advantage of greater bandwidth capability. It
    has the disadvantage of:
    a. Being harder to bend
    b. Smaller mechanical tolerances in connectors and splices
    c. Being difficult to couple light into
    d. B and C
    e. None of the above
    4. Describe with the aid of simple ray diagrams:
    a. The multimode step index fiber;
    b. The single-mode step index fiber.
    c. Compare the advantages and disadvantages of these two types of fiber

    for use as an optical channel.

    5.3 Mechanism of attenuation

    ACTIVITY 5.3: Light transmission analysis in optical fiber


    Fig.5. 11 The images to show the attenuation in optical fiber

    Observe the image clearly, and answer to the following questions:
    1. Does all the light from the source getting to the destination?
    2. What do you think is causing the loss in light transmission?
    3. What can be done to minimize that loss in the optical fibers above?
    Attenuation in fiber optics, also known as transmission loss, is the reduction
    in intensity of the light beam (or signal) as it travels through the transmission
    medium. Over a set distance, fiber optic with a lower attenuation will allow
    more power to reach its receiver than a fiber with higher attenuation.
    Attenuation can be caused by several factors both extrinsic and intrinsic:
    • Intrinsic attenuation is due to something inherent to the fiber such as
    impurities in the glass during manufacturing. The interaction of such
    impurities with light results in the scattering of light or its absorption.
    • Extrinsic attenuation can be caused by macro bending and
    microlending. A bent imposed on an optical fiber produce a strain in
    that region of the fiber and affects its refractive index and the critical
    angle of the light ray in that area. Macrobending that is a large-scale
    bent and microbending which is a small-scale bent and very localized
    are external causes that result in the reduction of optical power.
    Attenuation coefficients in fiber optics usually are expressed decibels per
    kilometer (dB/km) through the medium due to the relatively high quality of
    transparency of modern optical transmission media. It is observed that the
    attenuation is a function of the wavelength of the light. The attenuation αtot (λ ) 
    at wavelength λ of a fiber between two cross-sections, 1 and 2, separated by

    distance Lis defined, as    

    where egg P λ optical power at the cross-section 1, and egg P2 λ the optical power
    at the cross-section 2. Attenuation is an important limiting factor in the
    transmission of a digital signal across large distances. Thus, much research has
    gone into both limiting the attenuation and maximizing the amplification of the
    optical signal.
    5.3.1 Light scattering and absorption
    In the light transmission of signals through optical fibers, attenuation occurs
    due to light scattering and absorption of specific wavelengths, in a manner
    similar to that responsible for the appearance of color.
    a. Light scattering

    Scattering losses


    Fig.5. 12: Light scattering in optical fiber

    The propagation of light through the core of an optical fiber is based on total
    internal reflection of the light wave. Rough and irregular surfaces, even at the
    molecular level, can cause light rays to be reflected in random directions as it
    is illustrated on Fig.5.12. This is called diffuse reflection or scattering, and it is
    typically characterized by wide variety of reflection angles.
    Light scattering depends on the wavelength of the light being scattered.
    Thus, limits to spatial scales of visibility arise, depending on the frequency
    of the incident light-wave and the physical dimension (or spatial scale) of the
    scattering center, which is typically in the form of some specific micro-structural
    feature. Since visible light has a wavelength of the order of one micrometer (one
    millionth of a meter) scattering centers will have dimensions on a similar
    spatial scale. Thus, attenuation results from the incoherent scattering of light
    at internal surfaces and interfaces.
    b. Light absorption
    Material absorption is a loss mechanism related to the material composition
    and fiber fabrication process. This results in the dissipation of some transmitted
    optical power as heat in the waveguide. Absorption is classified into two basic
    categories: Intrinsic and extrinsic absorptions. (John, 2009)
    Intrinsic absorption: is caused by basic fiber material properties. If an optical
    fiber is absolutely pure, with no imperfections or impurities, ten all absorption
    will be intrinsic. Intrinsic absorption in the ultraviolet region is caused bands.
    Intrinsic absorption occurs when a light particle (photon) interacts with an
    electron and excites it to a higher energy level.
    5.3.2 Measures to avoid Attenuation
    The transmission distance of a fiber-optic communication system has
    traditionally been limited by fiber attenuation and by fiber distortion.
    • Repeaters: Repeaters convert the signal into an electrical signal, and
    then use a transmitter to send the signal again at a higher intensity
    than was received, thus counteracting the loss incurred in the previous
    segment. They mostly used to be installed about once every 20 km.
    • Regenerators: Optical fibers link, in common with any line
    communication system, have a requirement for both jointing and
    termination of the transmission medium. When a communications
    link must span at a larger distance than existing fiber-optic technology
    is capable of, the signal must be regenerated at intermediate points
    in the link by optical communications repeaters called regenerators.
    An optical regenerator consists of optical fibers with special coating
    (doping). The doped portion is pumped with a laser. When the
    degraded signal comes into the doped coating, the energy from the
    laser allows the doped molecules to become lasers themselves. The
    doped molecules then emit a new strong light signal with the same
    characteristics as the incoming weak signal. Basically, the regenerator
    is a laser amplifier for the incoming signal.
    • Optical Amplifiers: Another approach is to use an optical
    amplifier which amplifies the optical signal directly without having to
    convert the signal into the electrical domain. It is made by doping a
    length of fiber with the rare-earth mineral erbium and pumping it with
    light from a laser with a shorter wavelength than the communications
    signal (typically 980 nm). Amplifiers have largely replaced repeaters in
    new installations.
    5.3.3 Checking my progress
    1. True or False: One of the reasons fiber optics hasn’t been used in more
    areas has been the improvement in copper cable such as twisted pair.
    2. True or False: With current long-distance fiber optic systems using
    wavelength-division multiplexing, the use of fiber amplifiers has
    become almost mandatory.
    3. Fiber optics has extraordinary opportunities for future applications
    because of its immense bandwidth.
    a. True
    b. False
    4. a. What do we mean by attenuation in optical fibers?
    c. State two ways in which energy is lost in optical fibers.
    d. If a fiber loses 5% of its signal strength per kilometer, how much of

    its strength would be left after 20 km?

    5.4 OPTICAL TRANSMITTER AND OPTICAL RECEIVER
    ACTIVITY 5.4: Investigating the signal sources and signal receiver
    for optic fibers
    1. With the basic information you know about the functioning process
    of optical fiber, answer to the following questions.
    2. Where does the light that is transmitted into the optical fiber core
    medium come from?
    3. What are the type compositions of the light signal propagating into
    optical fiber?
    4. Discuss and explain the function principle of signal generators and
    signal receivers of light from optical fibers.
    The process of communicating using fier-optics involves the following basic
    steps:
    1. Creating the optical signal involving the use of a transmitter, usually from
    an electrical signal.
    2. Relaying the signal along the fier, ensuring that the signal does not
    become too distorted or weak.
    3. Receiving the optical signal.

    4. Converting it into an electrical signal

    Fig.5. 13: Optical fiber communication mechanism (Transmitter and receiver blocks).

    5.4.1 Transmitters
    The most commonly used optical transmitters are semiconductor devices
    such as light-emitting diodes (LEDs) and laser diodes. The difference between
    LEDs and laser diodes is that LEDs produce incoherent light, while laser diodes
    produce coherent light. For use in optical communications, semiconductor
    optical transmitters must be designed to be compact, efficient and reliable,
    while operating in an optimal wavelength range and directly modulated at high
    frequencies (see Fig.5.13: Transmitter block).
    In its simplest form, a LED is a forward-biased p-n junction, emitting
    light through spontaneous emission, a phenomenon referred to
    as electroluminescence. The emitted light is incoherent with a relatively wide
    spectral width of 30–60 nm. LED light transmission is also inefficient, with
    only about 1% of input power, or about 100 microwatts, eventually converted
    into launched power which has been coupled into the optical fiber. However, due
    to their relatively simple design, LEDs are very useful for low cost applications.
    5.4.2 The Optical Receivers
    The main component of an optical receiver is a photodetector (photodiode)
    which converts the infrared light signals into the corresponding electrical
    signals by using photoelectric effect before they are processed by the decoder
    for conversion back into information. The primary photo detectors for

    telecommunications are made from Indium gallium arsenide (see Fig.5.13).

    The photodetector is typically a semiconductor-based photodiode. Several

    types of photodiodes include p-n photodiodes, p-i-n photodiodes, and avalanche

    photodiodes. Metal-semiconductor-metal (MSM) photodetectors are also used

    due to their suitability for circuit integration in regenerators and wavelengthdivision

    multiplexers.

    5.4.3 Checking my progress

    1. Circle the three basic components in a fiber optic communications system.

    a. Telescope e. Maser fiber

    b. Transmitter f. Optical fiber

    c. Receiver G. Alternator

    d. Surveillance satellites

    2. Information (data) is transmitted over optical fiber by means of:

    a. Light d. Acoustic waves

    b. Radio waves e. None of the above

    c. Cosmic rays

    3. Connectors and splices add light loss to a system or link.

    a. True

    b. False

    4. Do fibers have losses?

    5.5. USES OF OPTICAL FIBERS
    ACTIVITY 6.5: Applications of fiber optics in telecommunication
    and in medicine
    Use the internet or the library to investigate the applications of optical
    fiber in medicine and telecommunication systems.
    5.5.1. Telecommunications Industry
    Optical fibers offer huge communication capacity. A single fiber can carry the
    conversations of every man, woman and child on the face of this planet, at the
    same time, twice over. The latest generations of optical transmission systems
    are beginning to exploit a significant part of this huge capacity, to satisfy the
    rapidly growing demand for data communications and the Internet.
    The main advantages of using optical fibers in the communications industry
    are: 
    1. A much greater amount of information can be carried on an optical fiber
    compared to a copper cable.
    2. In all cables some of the energy is lost as the signal goes along the cable.
    The signal then needs to be boosted using regenerators. For copper cable
    systems these are required every 2 to 3km but with optical fiber systems
    they are only needed every 50km.
    3. Unlike copper cables, optical fibers do not experience any electrical
    interference. Neither will they cause sparks so they can be used in explosive
    environments such as oil refineries or gas pumping stations.
    4. For equal capacity, optical fibers are cheaper and thinner than copper
    cables and that makes them easier to install and maintain.
    5.5.2 Medicine Industry
    The advent of practicable optical fibers has seen the development of much
    medical technology. Optical fibers have paved the way for a whole new field of
    surgery, called laproscopic surgery (or more commonly, keyhole surgery), which
    is usually used for operations in the stomach area such as appendectomies.
    Keyhole surgery usually makes use of two or three bundles of optical fibers.
    A “bundle” can contain thousands of individual fibers”. The surgeon makes a
    number of small incisions in the target area and the area can then be filled with
    air to provide more room.
    One bundle of optical fibers can be used to illuminate the chosen area, and
    another bundle can be used to bring information back to the surgeon. Moreover,
    this can be coupled with laser surgery, by using an optical fiber to carry the
    laser beam to the relevant spot, which would then be able to be used to cut the
    tissue or affect it in some other way.
    5.5.3 Checking my progress
    The basic unit of digital modulation is:
    a. Zero        c. A and B

    b. One         d. None of the above

    5.6 ADVANTAGES AND DISADVANTAGES OF OPTICAL FIBERS
    ACTIVITY 5.6: Advantages and disadvantages of optical fibers
    Use search internet or your library to investigate the advantages and
    disadvantages of fiber optics.
    Although there are many benefits to using optical fibers, there are also
    some disadvantages. Both are discussed below:fiber in medicine and
    telecommunication systems.
    5.6.1 Advantages
    • Capacity: Optical fibers carry signals with much less energy loss than
    copper cable and with a much higher bandwidth. This means that
    fibers can carry more channels of information over longer distances
    and with fewer repeaters required.
    • Size and weight: Optical fiber cables are much lighter and thinner than
    copper cables with the same bandwidth. This means that much less
    space is required in underground cabling ducts. Also they are easier for
    installation engineers to handle.
    • Security: Optical fibers are much more difficult to tap information from
    undetected; a great advantage for banks and security installations.
    They are immune to electromagnetic interference from radio signals,
    car ignition systems, lightning etc. They can be routed safely through
    explosive or flammable atmospheres, for example, in the petrochemical
    industries or munitions sites, without any risk of ignition.
    • Running costs: The main consideration in choosing fiber when
    installing domestic cable TV networks is the electric bill. Although
    copper coaxial cable can handle the bandwidth requirement over the
    short distances of a housing scheme, a copper system consumes far
    more electrical power than fiber, simply to carry the signals.
    5.6.2 Disadvantages
    • Price: In spite of the fact that the raw material for making optical fibers,
    sand, is abundant and cheap, optical fibers are still more expensive per
    metre than copper. Having said this, one fiber can carry many more
    signals than a single copper cable and the large transmission distances
    mean that fewer expensive repeaters are required.
    • Special skills: Optical fibers cannot be joined together (spliced) as an
    easily as copper cable and requires additional training of personnel
    and expensive precision splicing and measurement equipment.
    5.6.3 Checking my progress
    1. List two advantages of using optical fiber. __________________________
    2. The replacement of copper wiring harnesses with fiber optic cabling
    will increase the weight of an aircraft.
    a. True

    b. False

    END UNIT ASSESSMENT 5
    1. a. An endoscope uses coherent and non−coherent fiber bundle
    I. State the use of the coherent bundle and describe its arrangement
    of fibers.
    II. State the use of the non−coherent bundle and describe its
    arrangement of fibers.
    b. Each fiber has a core surrounded by cladding. Calculate the critical
    angle at the core−cladding interface.
    Refractive index of core = 1.52
    Refractive index of cladding = 1.
    2. (a)Fig.5.9 shows a ray of light travelling through an individual fiber
    consisting of cladding and a core. One part has a refractive index of

    1.485 and the other has a refractive index of 1.511.

    Fig.5. 9: Light transmission in optical fiber.

    I. State which part of the fiber has the higher refractive index and
    explain why.
    II. (ii) Calculate the critical angle for this fiber.
    (b) The figure below shows the cross-section through a clad optical

    fiber which has a core of refractive index 1.50.


    Complete the graph below to show how the refractive index changes

    with the radial distance along the line ABCD in the figure above.

    Fig.5. 11: Axes for the half life decay curve

    3.
    a. What do we mean by attenuation in optical fibers?
    b. State two ways in which energy is lost along the length of an
    optical fiber.
    c. If a fiber loses 5% signal strength per km, how much strength
    would be left after 20 km?
    4. Estimate the length of time it would take a fiber optic system to
    carry a signal from the UK to the USA under the Atlantic. (Take c =
    2 x 108 m/s in the cable. Estimate the length of the cable under the
    sea.
    a. Estimate the length of time it would take a microwave signal to
    travel from the UK to the USA a satellite Enk. (Geosynchronous
    satellites orbit at a height of about 36 000 Ian above the Earth’s
    surface.

    b. Which would give less delay in a telephone conversation?


  • UNIT 6 BLOCK DIAGRAM OF TELECOMMUNICATION

    Key unit competence: Construct and analyze block diagram of
    telecommunication systems.
    My goals
    • Identify parts of a block diagram of telecommunication system.
    • Differentiate oscillator, modulator and amplifier.
    • Outline the function of a microphone and antenna.
    • Describe terms applied in telecommunication systems
    • Construct, analyse and judge block diagrams of a telecommunication
    system.
    • Realise that parts of a telecommunication system are dependent
    INTRODUCTORY ACTIVITY
    Investigating the function of wireless microphone
    Materials:
    • Wireless microphone set
    • Amplifier and mixer
    • Connecting wires
    • Speaker
    Procedure:
    Connect the full sound system such that the signal will be transmitted to the
    speakers using wireless microphone.
    Questions:
    1. How is your voice getting to the speakers?
    2. Where else this system is used?

    3. What are advantages and disadvantages of communication?

    6.1. OPERATING PRINCIPLE OF MICROPHONE
    ACTIVITY 6.1: Investigating the function of a microphone
    Take the case of two people talking on telephone (see Fig.6.1). Observe

    the image below and answer to the following questions:

    Fig.6. 1 People talking on telephone

    1. Discuss the functioning process of a telephone.

    2. Differentiate the functions of a microphone from that of a speaker.

    Telecommunication in real life is the transmission of signals and other types
    of data of any nature by wire, radio, optical or other electromagnetic systems of
    communication. Telecommunication occurs when the exchange of information
    between communicating participants includes the use of signs or other
    technologically based materials such as telephone, TV set, radio receiver, radio
    emitter, computer, and so on. All can be done either mechanically, electrically
    or electronically.
    The use of microphones began with the telephone in the nineteenth century.
    The requirements were basically those of speech intelligibility, and the carbon
    microphone, developed early in that art, is still used in telephones today.
    Particles of carbon are alternately compressed and relaxed by the diaphragm
    under the influence of sound pressure, and the resulting alternation of
    resistance modulates the current proportionally to the change in resistance.
    Carbon microphones are noisy; they have limited dynamic range and produce
    high levels of distortion. However, none of these defects is really serious in its
    application to telephony.
    Operating principle of microphones
    A microphone converts sound vibrations into electrical entity. Basically a
    microphone has a diaphragm which moves when sound pressure pushes it. This
    movement can be converted into proportional voltage using several possible

    transducers.

    Fig.6. 2: The outer and internal view of a microphone

    A transducer is a device which receives electrical, mechanical or acoustic
    waves from one medium and converts them into related waves for a similar or
    different medium. Thus, it can be said that a microphone is a transducer that
    converts acoustical sound energy into electrical energy. Its basic function is
    therefore to convert sound energy into electrical audio signals which can be
    used for further processing. Microphones are classified based on construction

    and directivity.

    6.2 CHANNELS OF SIGNAL TRANSMISSION
    ACTIVITY 6.2: Investigating signal transmission
    Basing on the activity 6.1, explain and discuss how the voices are
    transmitted from our mouth to telephone and then to the receiver’s
    telephone
    An audio frequency (acronym: AF) or audible frequency is characterized as a
    periodicvibration whose frequency is audible to the average human. The SI unit
    of frequency is the hertz (Hz). It is the property of sound that most determines
    pitch. The generally accepted standard range of audible frequencies is 20Hz
    to 20 kHz, although the range of frequencies that individuals hear is greatly
    influenced by environmental factors. Frequencies below 20 Hz are generally
    felt rather than heard, assuming the amplitude of the vibration is great enough.
    Frequencies above 20 kHz can sometimes be sensed by young people. High
    frequencies are the first to be affected by hearing loss due to age and/or
    prolonged exposure to very loud noises.
    Modulation is the process of superimpose to a low frequency signal (original
    signal) a high frequency signal (carrier signal) for transmission. The resulting
    signal is a modulated or radio signal.
    6.2.1 Amplitude modulation (AM)
    It is a type of modulation, where the amplitude of the carrier wave is changed
    in accordance with the intensity of the signal. However, the frequency and the

    phase shift of the modulated wave remains the same.


    Fig.6. 3 A graphs of amplitude modulation

    Note that the amplitudes of both positive and negative half-cycles of carrier
    wave are changed in accordance with the signal. For instance, when the signal
    is increasing in the positive sense, the amplitude of carrier wave also increases.
    On the other hand, during negative half-cycle of the signal, the amplitude of
    carrier wave decreases. Amplitude modulation is done by an electronic circuit

    called modulator.

    6.2.2 Frequency modulation (FM).
    It is a type of modulation, where the frequency of the carrier wave is changed
    in accordance with the intensity of signal. The amplitude and the phase shift of
    the modulated wave remain the same. The frequency variations of carrier wave
    depend upon the instantaneous amplitude of the original signals. The carrier
    frequency increases and decreases respectively to its positive and negative peak

    values as the voltage of the original signal seem to approach its peak values.


    Fig.6. 4: Process of FM transmission

    Comparison of amplitude modulation and frequency modulation

    Table 6. 1: Comparison between FM and AM

    6.2.3 Short wave (SW)
    A short wave is any wave whose frequency ranges between 300 kHz and 3 MHz.
    In transmission, these waves are used for very long distance communication as
    their bands can be reflected or refracted from the ionosphere by an electrically

    charged layer with atoms in the atmosphere.

                                                                                     Fig.6. 5: Short wave illustration

    The short waves directed at an angle into the sky can be reflected back to Earth at

    great distances, beyond the horizon. This called sky wave or skip propagation.

    These waves are used for radio broadcasting of voice and music to shortwave

    listeners over very large areas; sometimes entire continents or beyond. They

    are also used for military communication, diplomatic communication, and twoway

    international communication by amateur radios enthusiasts for hobby.

    6.2.4 Medium wave (MW)

    Medium wave (MW) is the part of the medium frequency (MF) radio band
    used mainly for AM radio broadcasting. It is the original radio broadcasting
    band, in use since the early 1920’s. It is typically used by stations serving a local
    or regional audience. At night, medium wave signals are no longer absorbed by
    the lower levels of the ionosphere, and can often be heard hundreds or even
    thousands of miles away.

    For Europe the MW band ranges from 526.5 kHz to 1606.5 kHz, using channels
    spaced every 9 kHz, and in North America an extended MW broadcast band
    ranges from 525 kHz to 1705 kHz, using 10 kHz spaced channels.
    6.2.5 Checking my progress
    1. In transmission, the range of short waves are between
    a. Radio wave and microwave
    b. X-rays and gamma rays
    c. Infrared and visible light
    d. Infrared and ultraviolet
    2. Where Short waves can be used?
    3. Explain what is meant by Medium wave (MW)
    4. Distinguish between Amplitude modulation and frequency modulation
    6.3 CARRIER WAVE AND MODULATOR
    6.3.1 Concept of carrier wave modulation
    ACTIVITY 6.3: Modulation techniques

    What are applications of such a system shown in the below figure?

                                                     Fig.6. 6: Radio wave transmission

    Observe the mechanism above (Fig.6.6) and answer to the following
    questions
    1. Analyze the provided figure and explain the transmission process
    used there.

    2. What are applications of such a system shown in the above figure?

    Modulation is the process of varying the characteristics of carrier signal with
    the modulating signal or modulation is defined as the superimposition of low
    frequency baseband signal (modulating signal) over high frequency carrier
    signal by varying different parameters of the carrier signals (see Fig.6.6). Based
    on the types of parameters that are varied in proportion to the baseband (low
    frequency) signal, modulation is of different types. In digital modulation, the
    message signal is converted from analog into digital. In digital modulation
    techniques, the analog carrier signal is modulated by discrete signal. The carrier
    wave is switched on and off to create pulses such that signal is modulated.
    Low frequency signal (Baseband) communication is not commonly used for
    distance communication. Low frequency baseband signals, having low energy,
    if transmitted directly will get distorted. So baseband signal must be modulated
    with high frequency signal to increase the range of transmission.
    6.3.2 Checking my progress
    1. In………transmission, the carrier signal modulated so that its amplitude
    varies with the changing amplitudes of the modulating signal
    a. AM c. FM
    b. PM d. None of the above?
    2. Distinguish between analog signal and digital signal?
    3. What is meant by carrier wave in telecommunication?

    4. What is the application of a carrier wave in a telecommunication system?

    6.4 OSCIALLATOR, RADIO FREQUENCY AMPLIFIER AND
    POWER AMPLIFIER
    ACTIVITY 6.4: Investigating what is an oscillator and a radio
    frequency amplifier
    Make an intensive research on the properties and function of an
    oscillator and radio frequency amplifier. According to your findings,
    answer to the following questions:
    1. Explain a radio frequency amplifier and state its importance in
    telecommunication?
    2. What do you understand by an oscillator in telecommunication
    system? Discus its importance?

    3. Describe other uses of oscillator and radio frequency amplifier.

    6.4.1 Oscillator
    Oscillators are electronic circuits that produce a periodic waveform on its
    output with only the DC supply voltage as an input. The output voltage can
    be either sinusoidal or non-sinusoidal, depending on the type of oscillator, thus,
    the outputs signals can be sine waves, square waves, triangular waves, and saw

    tooth waves.

    Fig.6.7: Basic function of oscillator and radio frequency amplifier in telecommunication system

    The oscillation in any circuit will depend on the following properties:
    • Amplification of the used amplifier
    • A frequency determining device (receiver/ transmitter)
    • Signal regeneration (Positive feedback)
    Factors which may fluctuate the operating frequency
    • Long time of operation
    • Heat that is generated along the operation
    • Operating point of the active elements
    • Frequency dropper elements (capacitors, inductors)
    • Change in total opposition faced by the alternating current (impedance)
    Oscillators may be classified in three ways, including:
    a. The design principle used where we have a positive and a negative
    feedback oscillators,
    b. The frequency range of the signal over which they are used:
    • Audio Frequency (AF) oscillators (frequency range is 20 Hz to 20 kHz)
    • Radio Frequency (RF) oscillators (frequency range is 20 kHz to 30
    MHz)
    • Video Frequency oscillators (frequency range is dc to 5 MHz)
    • High Frequency (HF) oscillators (frequency range is 1.5 MHz to 30
    MHz)
    • Very High Frequency (VHF) oscillators (frequency range is 30 MHz to
    300 MHz)
    c. The nature of generated signals where we have:
    • Sinusoidal Oscillators: These are known as harmonic oscillators and
    are generally LC tuned-feedback or RC tuned-feedback type oscillator
    that generates a sinusoidal waveform which is of constant amplitude
    and frequency.
    • Non-sinusoidal Oscillators: These are known as relaxation oscillators
    and generate complex non-sinusoidal waveforms that changes very
    quickly from one condition of stability to another such as square-wave,

    triangular-wave or sawtooth-wave type waveforms

    Fig.6. 8: Types of signals output of an oscillator

    The oscillators have a variety of applications. In some applications we need
    voltages of low frequencies, in others of very high frequencies. For example
    to test the performance of a stereo amplifier, we need a signal of variable
    frequency in the audio range (20 Hz-20 KHz). Next to amplifiers, oscillators
    are the most important analog circuit block. Oscillators can be found in almost
    every imaginable electronic system. For example all radio receiving systems
    must have a local oscillator. All transmitting systems require oscillators to
    define the carrier frequency. Similarly, most digital systems are clocked and
    require a master clock oscillator to operate. Signal sources, which are essential
    for testing electronic systems, are also precise oscillators whose frequency and
    amplitude can be accurately set according to the requirement.
    6.4.2 Radio frequency amplifier
    An amplifier is an electronic device which can increase the amplitude or the
    power of the input signal to its input parts, without the needs of modifying
    the form of that signal. Mostly, these devices are used in telecommunication,
    especially in receivers. Any amplifier has an active element, more often
    transistors, though there may exist also resistors, inductors and capacitors.
    Classes of amplifiers
    There exist two classes: Capacitor coupled amplifiers and transformer
    coupled amplifiers. The two are used in multistage amplifiers, that is when
    we connect two stage amplifiers using a capacitor and when we connect two
    stages amplifiers using a transformer, we get a capacitor coupled amplifier and
    a transformer coupled amplifier respectively.
    Characteristics of RF amplifier
    1. It may require or not a wide bandwidth signal to amplify
    2. The output signal from the RF amplifier may or not be linear
    3. They require to operate at a narrow bandwidth
    4. They can use filters to reduce bandwidth

    5. To tune the circuit, the resonant frequency is set to  

    All electronic devices have an inductive reactance and capacitive reactances. The
    latter are vary as the frequency fluctuates. Normally, as the frequency increases,
    the inductive reactance increases but capacitive reactance decreases. Then
    the circuit will be called self-resonate at point, where the two characteristics
    mentioned above become equal.
    In signal processing, we need to realize as many operations as possible so
    that we arrive to a signal that fits the transmission standards. The signal to be
    modulated is referred to as a baseband signal. The carrier signal needs to be a
    higher frequency than the baseband. A RF amplifier is a device which amplifies
    the baseband signal. However, devices such as Oscillators, Mixers, Multipliers
    and frequency synthesizers can be used to meet the above conditions.
    6.4.3 Power Amplifier
    Signals are amplified in several stages (Fig.6.9). The initial stages are small
    signal amplifiers, they are designed to give good voltage gain, so they are called
    voltage amplifiers. At the final stage, the signal becomes large, the large-signal

    amplifier is called power amplifier, as it is designed for good power gain.

    Fig.6. 9 The functioning mechanism of power amplifier

    The Fig.6.10 shows that the power amplifiers are classified according to the
    conduction angle they produced. Conduction angle measures the portion of
    the input cycle that is reproduced at the output of a power amplifier. If the
    conduction angle is 360°, which means that all of the input cycle is reproduced,

    the amplifier is called class A amplifier.

    Fig.6. 10: The conduction angle of power amplifier

    Every amplifier has a DC equivalent circuit and an AC equivalent circuit.
    Because of this, it has two load lines : a Dc load line and an AC load line.
    6.4.4 Checking my progress
    1. State the classifications of oscillators according to Frequency Band of
    the Signals
    2. Explain what is mean by Oscillator
    3. The figure is about transmission of signals in telecommunication. Study

    it carefully and label it.

    6.5 ANTENNAS
    ACTIVITY 6.5: Defining types of antennas
    Observe clearly the images on the fig. 6.11 below and answer the

    questions that follow:

                                                             Fig.7. 11 Different types of antenna

    1. Describe the different the types of antenna shown in the Fig.7.11
    above.
    2. Discuss other different types of antenna you know.
    3. Discuss and explain the function principle of an antenna.
    An antenna or aerial is an electrical device connected (often through a
    transmission line) to the receiver or transmitter which converts electric power
    into radio waves, and vice versa. It is usually used with a radio transmitter
    or radio receiver. In transmission, a radio transmitter supplies an oscillating
    radio frequency electric current to the antenna’s terminals, and the antenna
    radiates the energy from the current as electromagnetic waves (radio waves).
    In reception, an antenna intercepts some of the power of an electromagnetic
    wave in order to produce a tiny voltage at its terminals, which is fed to a receiver
    to be amplified.
    Antennas are essential components of all equipment which are used in radio.
    They are used in broadcasting systems, broadcast television systems, two-way
    radio systems, communications receiver’s systems, radar systems, cell phones
    systems, and satellite communications systems, garage door openers systems,
    wireless microphones systems, Bluetooth enabled devices systems, wireless
    computer networks systems, baby monitors systems, and Radio Frequency
    Identification (RFID) tags systems on merchandise etc.
    6.5.1 Types of antennas
    There are a very large variety of antennas used in telecommunication. Here we
    can discuss at least four types of antenna among others.
    Wire antennas
    The wire antennas are dipole, monopole, loop antenna, helix and are usually
    used in personal applications, automobiles, buildings, ships, aircrafts and super

    crafts.

    Aperture antennas
    These are horn antennas and waveguide opening and they are usually used in

    aircrafts and space crafts because they are flush-mounted.

                 Fig.6. 13: A horn antenna with aperture field distribution

    Reflector antennas
    These are parabolic reflectors and corner reflectors and they are high gain
    antennas usually used in radio astronomy, microwave communication and

    satellite tracking.


                 Fig.6. 14: Reflector antenna

    Array antennas
    These are also called Yagi-Uda antennas or micro-strip patch arrays or
    aperture arrays, slotted waveguide arrays. They are suitable for very high gain

    applications with added advantage, such as, controllable radiation pattern.


               Fig.6. 15: Array antenna.

    6.5.2 Checking my progress

    1. What is meant by an antenna in telecommunication system?

    2. State and explain at least two types of antenna

    6.6 BLOCK DIAGRAMS OF TELECOMMUNICATION

    ACTIVITY 6.6: Investigating communication block


    Information: Information is any entity or form that resolves uncertainty or
    provides the answer to a question of some kind. It is thus related to data and
    knowledge, as data represents values attributed to parameters, and knowledge
    signifies understanding of real things or abstract concepts. Message: A message
    is a term standing for information put in an appropriate form for transmission.
    Each message contains information. A message can be either analog message
    (a physical time variable quantity usually in smooth and continuous form) or
    a digital message (anordered sequence of symbols selected from finite set of
    elements) as shown in Fg.6.19.
    • Analog message: a physical time-variable quantity usually in smooth
    and continuous form.
    • Digital message: ordered sequence of symbols selected from finite set
    of elements.
    A signal is a mathematical function representing the time variation of a physical
    variable characterizing a physical process and which, by using various models,
    can be mathematically represented. In telecommunication, the message is also
    known as a signal and the signal is transmitted in an electrical or voltage form.

    ( i.e Signal ≈ Message)


                 Fig.6. 17: Analog signal and digital signal representation diagram

    COMPARISON OF AN ANALOG SIGNAL TO A DIGITAL SIGNAL
    As discussed in the previous section, we can have the summary of differences

    between analog signal and digital signal (see Table 6.2)

                         Table 6. 2: Comparison of an analog signal to a digital signal

    SOME ELEMENTS OF BLOCK DIAGRAM OF TELECOMMUNICATION
    1. Transmission channel which is the electric medium that bridges the
    distance from source to destination
    2. The receiver to convert the received signal in a form appropriate for the
    output transducer after amplifying, filtering, demodulating and decoding it
    3. Output transducer to convert the output electrical signal the desired
    message form
    4. Modulation is defined as the process by which some characteristics (i.e.
    amplitude, frequency, and phase) of a carrier are varied in accordance with
    a modulating wave.
    5. Encoding is the process of coding the message and changes it in the
    language understandable by the transmitter. This operation is realized at
    the transmitting end
    6. Demodulation is the reverse process of modulation, which is used to
    get back the original message signal. Modulation is performed at the
    transmitting end whereas demodulation is performed at the receiving end
    7. Decoding is the reverse process of encoding to retrieve the original
    message and make it human understandable message. It is realized at the
    receiving end
    8. Antennas which are aerials used to transmit and receive the signals.
    9. The oscillators which are the sources of carrier signals which are used to
    modulate and help the original signal to reach the destination
    10. The signal normally, must be raised at a level that will permit it to reach its

    destination. This operation is accomplished by amplifiers


                 Fig.6. 18: Block diagram of telecommunication

    6.6.1 Simple radio transmitter
    A radio transmitter consists of several elements that work together to generate
    radio waves that contain useful information such as audio, video, or digital
    data. The process by which a radio station transmits information is outlined in

    Fig. 6.21.


    Fig.6. 19: Block diagram of a radio transmitter

    • Power supply: Provides the necessary electrical power to operate the
    transmitter.
    • The audio (sound) information is changed into an electrical signal
    of the same frequencies by, say, a microphone, a laser, or a magnetic
    read write head. This electrical signal is called an audio frequency
    (AF) signal, because the frequencies are in the audio range (20 Hz to
    20 000 Hz).
    • The signal is amplified electronically in AF amplifier and is then mixed
    with a radio-frequency (RF) signal called its carrier frequency, which
    represents that station. AM radio stations have carrier frequencies
    from about 530 kHz to 1700 kHz. Today’s digital broadcasting uses the
    same frequencies as the pre-2009 analog transmission.
    • The Modulator or Mixer adds useful information to the carrier wave.
    The mixing of the audio and carrier frequencies is done in two ways.
    - In amplitude modulation (AM), the amplitude of the highfrequency
    carrier wave is made to vary in proportion to the
    amplitude of the audio signal, as shown in Fig.6.3. It is called
    “amplitude modulation” because the amplitude of the carrier is
    altered (“modulate” means to change or alter).
    - In frequency modulation (FM), the frequency of the carrier wave
    is made to change in proportion to the audio signal’s amplitude,
    as shown in Fig.7.4. The mixed signal is amplified further and
    sent to the transmitting antenna (Fig.6.13.C), where the complex
    mixture of frequencies is sent out in the form of EM waves.
    • Amplifier: Amplifies the modulated carrier wave to increase its power.
    The more powerful the amplifier, the more powerful the broadcast.
    In digital communication, the signal is put into digital form which modulates the
    carrier. A television transmitter works in a similar way, using FM for audio and
    AM for video; both audio and video signals are mixed with carrier frequencies.
    6.6.2 Simple radio receiver
    A radio receiver is the opposite of a radio transmitter. It uses an antenna to
    capture radio waves, processes those waves to extract only those waves that are
    vibrating at the desired frequency, extracts the audio signals that were added
    to those waves, amplifies the audio signals, and finally plays them on a speaker.
    Now let us look at the other end of the process, the reception of radio and TV
    programs at home. A simple radio receiver is graphed in Fig. 6.22. The EM

    waves sent out by all stations are received by the antenna.


    Fig.6. 20 Block diagram of a simple radio receiver

    The signalantennadetect and send the radio waves,to the receiver are very
    small and contain frequencies from many different stations. The receiver uses
    a resonant LC circuit to select out a particular RF frequency (actually a narrow
    range of frequencies) corresponding to a particular station.
    A simple way of tuning a station is shown in Fig.6.23. When the wire of antenna
    is exposed to radio waves, the waves induce a very small alternating current in

    the antenna.


    Fig.6. 21: Simple tuning stage of a radio.

    A particular station is “tuned in” by adjusting the capacitance C and/or
    inductance L so that the resonant frequency of the circuit equals that of the
    station’s carrier frequency. R.F. Amplifier: A sensitive amplifier that amplifies
    the very weak radio frequency (RF) signal from the antenna so that the signal
    can be processed by the tuner.
    R.F. Tuner: A circuit that can extract signals of a particular frequency from a
    mix of signals of different frequencies. On its own, the antenna captures radio
    waves of all frequencies and sends them to the RF amplifier, which dutifully
    amplifies them all. Unless you want to listen to every radio channel at the same
    time, you need a circuit that can pick out just the signals for the channel you
    want to hear. That’s the role of the tuner.
    The tuner usually employs the combination of an inductor (for example, a coil)
    and a capacitor to form a circuit that resonates at a particular frequency. This
    frequency, called the resonant frequency, is determined by the values chosen
    for the coil and the capacitor. This type of circuit tends to block any AC signals
    at a frequency above or below the resonant frequency.
    You can adjust the resonant frequency by varying the amount of inductance
    in the coil or the capacitance of the capacitor. In simple radio receiver circuits,
    the tuning is adjusted by varying the number of turns of wire in the coil. More
    sophisticated tuners use a variable capacitor (also called a tuning capacitor) to

    vary the frequency.

    6.6.3 Wireless Radio Communication

    Let us now discuss the basic principles of wireless radio communications.
    We shall mainly concentrate on the principle of amplitude modulation and
    demodulation. The simplest scheme of wireless communication would be
    to convert the speech or music to be transmitted to electric signals using a
    microphone, boost up the power of the signal using amplifiers and radiate the
    signal in space with the air of an antenna. This would constitute the transmitter.
    At the receiver end, one could have a pick-up antenna feeding the speech or

    music signal to an amplifier and a loud speaker. (See Fig.6.24)

    Fig.6. 22 Wireless radio communication

    The above scheme suffers from the following drawbacks:
    i. EM waves in the frequency range of 20 Hz to 20 kHz (audio-frequency
    range) cannot be efficiently radiated and do not propagate well in space.
    ii. Simultaneous transmission of different signals by different transmitters
    would lead to confusion at the receiver.
    In order to solve these problems; we need to devise methods to convert or
    translate the audio signals to the radio-frequency range before transmission and
    recover the audio-frequency signals back at the receiver. Different transmitting
    stations can then be allotted slots in the radio-frequency range and a single
    receiver can then tune into these transmitters without confusion.
    The frequency range 500 kHz to 20 MHz is reserved for amplitude-modulated
    broadcast, which is the range covered by most three band transistor radios. The
    process of frequency translation at the transmitter is called modulation. The
    process of recovering the audio-signal at the receiver is called demodulation. A

    simplified block diagram of such a system is shown in the below figure.


    Fig.6. 23 Block diagram of radio transmitter and receiver

    6.6.4 Checking my progress
    1. What is the importance of power amplifier in simple radio transmitter.
    2. What do you understand by the following terms.
    3. Analog message
    4. Digital message
    5. Draw a circuit diagram of a simple radio receiver
    END UNIT ASSESSMENT 6
    A. Multiple choices
    1. One of the following is used for satellite communication
    a. Radio waves c. Microwaves
    b. Light waves d. All of these
    2. Amplitude –modulated radio waves are received by a tuned radiofrequency
    ( trf) Receiver. The receiver has a suitable detector
    circuit in order to
    a. Amplifier the carrier waves
    b. Amplifier the audio-frequencies carried
    c. Rectifier the carrier waves
    d. detect the carrier waves
    e. Transfer the audio-frequencies to the radio-frequency
    amplifier
    B. Structured questions
    3. What do you understand by the following terms?
    a. Amplifier
    b. Modulator
    4. What is meant by telecommunication system?
    5. Draw a labeled diagram showing the elements of radio transmitter
    C. Essay question
    6. Recently, the government of Rwanda decided to replace analog
    system of communication by digital system of communication.
    Debate about this government policy
    7. Explain briefly positive impact of telecommunication in development

    of a country like Rwanda.


  • UNIT 7 NATURE OF PARTICLES AND THEIR INTERACTIONS

    Key unit competence: Organize the properties and basic principles of quarks.
    My goals
    • The key varieties of fundamental subatomic particles and how they
    were discovered.
    • Distinguish between fundamental particles and composite particles
    • Distinguish between particles and antiparticles
    • Describe how antimatter can be used as a source of energy
    • State some applications for elementary particles
    • Compare matter and antimatter
    • The four ways in which subatomic particles interact with each other.
    • Analyze the structure of protons, neutrons, and other particles can be

    explained in terms of quarks

    INTRODUCTORY ACTIVITY

    Investigating the elementary particles discovery
    In the study of matter description and energy as well as their interactions;
    the fascinating thing of discovery is the structure of universe of unknown
    radius but still to know the origin of matter one need to know about small
    and smallest composites of matter. The smallest particle was defined to be
    electron, proton, and neutron. But one can ask:
    1. Are electron, proton and neutron the only particle that can define the
    origin of matter?
    2. What are other particles matter is composed of?

    3. Describe and discuss how particles interact with energy to form matter

    7.1 ELEMENTARY PARTICLES.
    7.1.1 Introduction
    ACTIVITY 7.1: Investigate the presence of smaller particles

    1. Use internet and retrieve the definition and the information about
    elementary particles, and then answer to the following questions.
    2. What does elementary particle physics talk about?
    3. What are the elementary particles found through your research?
    4. Discuss and explain the use of knowledge about the elementary

    particles.

    Particle physics, also known as high-energy physics, is the field of natural
    science that pursues the ultimate structure of matter.
    The protons and neutrons are collectively called hadrons, were considered
    as elementary particles until 1960. We now know that they are composed of
    more fundamental particles, the quarks. Electrons remain elementary to
    this day. Muons and τ-leptons, which were found later, are nothing but heavy
    electrons, as far as the present technology can tell, and they are collectively
    dubbed leptons.
    Quarks and leptons are the fundamental building blocks of matter. The
    microscopic size that can be explored by modern technology is nearing

    . The quarks and leptons are elementary at this level (Nagashima, 2013).

    Particle physics is the study of the fundamental constituents of matter and
    their interactions. However, which particles are regarded as fundamental have
    changed with time as physicists’ knowledge has improved. Modern theory called
    the standard model attempts to explain all the phenomena of particle physics
    in terms of the properties and interactions of a small number of particles of
    three distinct types (see Fig.7.1):
    • Two families of fermions (of spin ½): leptons and quarks

    • One family of bosons (of spin 1)

    Fig.7. 1 Fundamental Standard model of elementary particle

    I, II and III represent the first, second and the third generations. In addition,
    at least one spin-0 particle, called the Higgs boson, is postulated to explain the
    origin of mass within the theory, since without it all the particles in the model
    are predicted to have zero mass (see Fig.7.1).

    All the particles of the standard model are assumed to be elementary; i.e. they
    are treated as point particles, without internal structure or excited states. The
    most familiar example of a lepton is the electron (the superscript denotes the
    electric charge), which is bound in atoms by the electromagnetic interaction,
    one of the four fundamental forces of nature. A second well-known lepton is
    the electron neutrino, which is a light, neutral particle observed in the decay
    products of some unstable nuclei (the so-called β-decays). The force responsible

    for the β-decay of nuclei is called the weak interaction.

    7.1.2 Checking my progress

    1. Particles that make up the family of Hadrons are:
    a. Baryons and mesons                                 c. Protons and electrons
    b. Leptons and baryons                                d. Muons and Leptons
    2. Using the elementary particles, Complete the following sentences
    I. One family of bosons of spin 1 called__________ which act as ‘force
    carriers’ in the theory
    II. Two fermions of spin 1/2 called_________ and ________
    3. The first antiparticle found was the
    a. Positron                                        c. Quark
    b. Hyperons                                     d. baryon

    4. Explain what is meant by particle physics?

    7.2 CLASSIFICATION OF ELEMENTARY PARTICLES.
    ACTIVITY 7.1: Classes of elementary particles

    Based on the previous introduction section, reread the text and the
    answer to the following questions.
    1. What are the types of elementary particles?

    2. What properties are based on to classify elementary particles?

    There are three properties that describe an elementary particle ‘’mass,’’
    ‘’charge’’ and ‘’spin’’. Each property is assigned as number value. These
    properties always stay the same for an elementary particle.
    Mass (m): a particle has mass if it takes energy to increase its speed or
    to accelerate it. The values are given in MeV/C2
    . This comes from special
    relativity, which tells us that energy equals mass times the square of
    the speed of light. 2 E mc = × . All particles with mass are affected by
    gravity even particles with no mass like photon.
    Electric charge (Q): particles may have positive, negative charge or
    none. If one particle has a negative charge and another particle has a
    positive, the two particles are attracted to each other. If particles have
    a similar charge, they repel each other. At a short distance this force
    is much stronger than the force of gravity which pulls all particles
    together. An electron has a charge -1 and a proton has a charge +1. A
    neutron has average charge 0. Normal quarks have charge of 2/3 or

    -1/3

     Spin: the angular momentum or constant turning of particles has a
    particular value, called its spin number. Spin for elementary particle
    is 0, 1 or . The spin property only donates the presence of angular

    momentum. 

    7.2.1 Classification of particles by mass
    The most basic way of classifying particles is by their mass. The heaviest
    particles are the hadrons and the lightest one is the leptons.

    As seen the diagram above hadrons group is divided into baryons and mesons.

    Baryons are the heaviest particles and are followed by mesons.
    Hadrons are composite particles made of quarks held together by the strong
    force in a similar way as molecules are held together by electromagnetic force.
    They are subjected to the strong nuclear force and are not fundamental particles

    as they are made up of quarks. 

     Baryons are composite sub-atomic particle made up of 3 quarks
     (triquarks are distinct from mesons which are composed of one quark and
    one antiquark). Baryon comes from Greek word which means “heavy”.
    The protons are only stable baryons; all other baryons eventually decay

    into proton. 

    Ex: Protons and neutrons.
    • Mesons are hadrons sub-atomic particles made up of one quark and

    one anti-quark bound together by strong interaction. Ex: Pion and kaon
    Each pion has quark and one anti-quark therefore is a meson. 
    It is the lightest meson and generally the lightest hadrons. They are unstable.


    Leptons do not interact via the strong force. They carry electric charge also interact

    via the weak nuclear force. They include electron, muons, tau and three the types
    of neutrino: the electron neutrino (νE), the muon neutrino (νμ
    ) and the tau neutrino
    egg vτ . 


    In summary, leptons are subjected to the weak nuclear force and they do not
    feel the strong nuclear force.
    Examples: Electron, muons and neutrino.



    7.2.2 Classification of particles by spin.



    The spin classification determines the nature of energy distribution in a
    collection of particles. Particles of integer spin obey Bose-Einstein statistics
    whereas those of half-integer spin behave according to Fermi-Dirac statistics
    as shown in the following chart




    Fermions are particles which have half-integer spin and therefore are
    constrained by the Pauli Exclusion Principle (see Section 7.4). It includes
    electrons, protons and neutrons.



    The fact that electrons are fermions is foundational to the buildup of the
    periodic table of elements since there can be only one electron for each state
    in an atom (only one electron for each possible set of quantum numbers).
    The fermion nature of electrons also governs the behavior of electrons in a
    metal where at low temperatures all the low energy states are filled up to a
    level called the Fermi energy. This filling of states is described by Fermi-Dirac
    statistics.



    7.2.3 Checking my progress







    7.3 ANTI PARTICLE AND PAULI’S EXCLUSION PRINCIPLE

    7.3.1 Concept of particle and antiparticle
    ACTIVITY 7.3
    Discuss the following terms:
    1. Particle
    2. Antiparticle

    There are two important points about pair production. The first is that you need
    to collect energy to produce the electron-positron pair. You need the equivalent
    rest mass of energy that is the amount of energy contained in the both particle
    and anti-particle when at rest. The energy converted to mass is ‘lost’ or fully
    ‘’bound’’ until the particle is annihilated and the energy can be recovered. The
    second thing is that it needs a correct environment. The process does not occur
    unless certain conditions are present.


    Viewing the phenomena as a creative process we can say a threshold amount

    of energy is sacrificed in a correct context to manifest a pair of particle with
    a physical mass. It can be said something was created out of nothing. That is 
    before the interaction, no particles with mass existed. After interaction, there
    were two particles with mass. Hence something was created out of nothing.
    But this can be said only because of the perspective taken when viewing the
    process.


    For every charged particle of nature, whether it is one of the elementary

    particles of the standard model, or a hadron, there is an associated particle
    of the same mass, but opposite charge, called its antiparticle. 



    This result is a necessary consequence of combining special relativity with

    quantum mechanics. This important theoretical prediction was made by Dirac
    and follows from the solutions of the equation he first wrote down to describe
    relativistic electrons


    7.3.2 Pauli’s exclusion principle,

    Pauli’s exclusion principle is a quantum mechanical principle which states
    that:
    “Two or more identical fermions (particles with half-integer spin) cannot
    occupy the same quantum state simultaneously.”




    In case of electrons in atoms it can be stated as follows: it is impossible for two
    electrons of a poly-electron atom to have the same values of the four quantum
    numbers:


    The principle quantum number No, the angular momentum quantum number
    (l), the magnetic quantum number (ml) and the spin quantum number (ms). 


    For example, if two electrons reside in the same orbital and if their msmust be
    different and thus like electrons must have opposite half integer spin projections 


    This principle was formulated by Austrian physicist Wolfgang Pauli in 1925 for
    electrons, and later extended to all fermions with his spin–statistics theorem of
    1940.


    Particles with an integer spin, or bosons, are not subject to the Pauli Exclusion
    Principle: any number of identical bosons can occupy the same quantum state,
    for instance, photons produced by a laser and Bose–Einstein condensate.


    The Pauli Exclusion Principle describes the behavior of all fermions (particles
    with “half-integer spin”), while bosons (particles with “integer spin”) are
    subject to other principles. Fermions include elementary particles such 


    7.3.3 Checking my progress
    1. What do you understand by antiparticle?
    2. State Pauli’s exclusion principle?
    3. Why Pauli’s exclusion Principle is known as exclusion?

    7.4 FUNDAMENTAL INTERACTIONS BY PARTICLE EXCHANGE
    ACTIVITY 7.4: Fundamental interaction

    Using internet, discusses the fundamental interactions in terms of
    exchange particles, then find the relation between the following concepts.
    1. Gravitational forces
    2. electroweak force,
    3. Strong force and
    4. Weak forces. 

    7.4.1 Forces and Interactions


    have recognized three basic forces:











    • The gravitational force is an inherent attraction between two masses.
    Gravitational force is responsible for the motion of the planets and
    Stars in the Universe. It is carried by Graviton. By Newton’s law of
    gravitation, the gravitational force is directly proportional to the
    product of the masses and inversely proportional to the square of
    the distance between them. Gravitational force is the weakest force
    among the fundamental forces of nature but has the greatest large−
    scale impact on the universe. Unlike the other forces, gravity works
    In the 1860s, the Scottish physicist James Clerk Maxwell developed a theory
    that unified the electric andmagnetic forces into a single electromagnetic force.
    Maxwell’s electromagnetic force was soon found to be the “glue” holding atoms,
    molecules, and solids together. It is the force between charged particles such
    as the force between two electrons, or the force between two current carrying
    wires. It is attractive for unlike charges and repulsive for like charges. The 
    universally on all matter and energy, and is universally attractive

    • The electric force is a force between charges
    • The magnetic force, which is a force between magnets or between
    magnetic body and ferromagnetic body.
    electromagnetic force obeys inverse square law. It is very strong compared
    to the gravitational force. It is the combination of electrostatic and magnetic forces.

    The discovery of the atomic nucleus, about 1910, presented difficulties that
    could not be explained by either gravitational or electromagnetic forces.
    The atomic nucleus is an unimaginably dense ball of protons and neutrons.
    But what holds it together against the repulsive electric forces between the
    protons? There must be an attractive force inside the nucleus that is stronger
    than the repulsive electric force. This force, called the strong force, is the force
    that holds the protons and neutrons together in the nucleus of an atom. It is the
    strongest of all the basic forces of nature. It, however, has the shortest range,
    of the order of 10−15 m. This force only acts on quarks. It binds quarks together
    to form baryons and mesons such as protons and neutrons. The strong force is
    mediated or carried by Gluons. Quarks carry electric charge so they experience

    electric and magnetic forces.

    In the 1939, physicists found that the nuclear radioactivity called beta decay
    could not be explained by either the electromagnetic or the strong force. Careful
    experiments established that the decay is due to a previously undiscovered
    force within the nucleus. The strength of this force is less than either the strong
    force or the electromagnetic force, so this new force was named the weak
    force. Weak nuclear force is important in certain types of nuclear process such
    as β-decay. This force is not as weak as the gravitational force. The weak force
    acts on both leptons and quarks (and hence on all hadrons). The weak force is
    carried by W+, W- and Z. Leptons – the electrons, muons and tau – are charged

    so they experience electric and magnetic forces.

    Of these, our everyday world is controlled by gravity and electromagnetism. The
    strong force binds quarks together and holds nucleons (protons & neutrons)
    in nuclei. The weak force is responsible for the radioactive decay of unstable

    nuclei and for interactions of neutrinos and other leptons with matter. 

    By 1940, the recognized forces of nature (fundamental forces)were four:
    • Gravitational forces between masses,
    • Electromagnetic forces resulting from the combination of electric and
    magnetic fields,
    • Strong force (nuclear force) between subatomic particles,
    • Weak forces that arise in certain radioactive decay processes.

    By 1980, Sheldon Glashow, Abdus Salam, and Steven Berg developed a theory
    that unifies electromagnetism and weak force into electroweak force. Hence, 

    our understanding of the forces of nature is in terms of
    three fundamental

    forces: 

    • The gravitational force,
    • The electroweak force,

    • The strong force. 

    The Table 7.1 below summaries the fundamental forces and force carriers.



    W boson: short-lived elementary particle; one of the carriers of the
    weak nuclear force
    • Z boson: short-lived elementary particle; one of the carriers of the
    weak nuclear force
    • Graviton: the hypothetical particle predicted to carry the gravitational

    force

    All the forces of nature should be capable of being described by single theory.
    But only at high energies should be the behavior of the forces combines, this is
    called unification. We can compare the relative strengths of the electromagnetic
    repulsion and the gravitational attraction between two protons of unit charge

    using the above equations.

    EXAMPLE 7.1


    Thus the gravitational is the weakest of the fundamental forces. These

    interactions and their relative strengths are summarized in Table 7.1

    7.4.2 Checking my progress

    1. Particles that interact by the strong force are called:
    a. Leptons                               c. Muons
    b. hadrons                             d. Electrons

    2. Name the four fundamental interaction and the particles that mediate each

    7.5 UNCERTAINTY PRINCIPLE AND PARTICLE CREATION

    7.5.1 The concept of uncertainty principle

    ACTIVITY 7.5: Investigation of particle creation and position.

    Basing on the knowledge and skills obtained from the previous sections
    of this unit, use internet to find the meaning of the particle creation.
    a. Is it possible to know the exact location of an elementary particle?

    b. Discuss and explain your findings

    The discovery of the dual wave–particle nature of matter forces us to re-evaluate

    the kinematic language we use to describe the position and motion of a particle.

    In classical Newtonian mechanics we think of a particle as a point. We can
    describe its location and state of motion at any instant with three spatial
    coordinates and three components of velocity. But because matter also has a
    wave aspect, when we look at the behaviour on a small enough scale comparable
    to the de Broglie wavelength of the particle we can no longer use the Newtonian
    description. Certainly no Newtonian particle would undergo diffraction like

    electrons do.

    To demonstrate just how non Newtonian the behaviour of matter can be, let’s
    look at an experiment involving the two-slit interference of electrons (Fig.7.4).
    We aim an electron beam at two parallel slits, just as we did for light. (The
    electron experiment has to be done in vacuum so that the electrons don’t collide

    with air molecules.) 

    What kind of pattern appears on the detector on the other side of the slits?

    The answer is: exactly the same kind of interference pattern we saw for photons.
    Moreover, the principle of complementarily, tells us that we cannot apply the
    wave and particle models simultaneously to describe any single element of
    this experiment. Thus we cannot predict exactly where in the pattern (a wave
    phenomenon) any individual electron (a particle) will land. We can’t even ask
    which slit an individual electron passes through. If we tried to look at where the
    electrons were going by shining a light on them that is, by scattering photons
    off them the electrons would recoil, which would modify their motions so that

    the two-slit interference pattern would not appear.

    Just as electrons and photons show the same behaviour in a two-slit interference
    experiment, electrons and other forms of matter obey the same Heisenberg

    uncertainty principles as photons do:

    Heisenberg uncertainty principle for position and momentum is given by

    This is a mathematical statement of the Heisenberg uncertainty principle Or
    it is sometimes called, the indeterminacy principle. It tells us that we cannot
    measure both the position and momentum of an object precisely at the same

    time.

    The uncertainty principle relates energy and time, examining this as follows.
    The object to be detected has an uncertainty in position   the photon that
    detects it travels with speed c, and it takes a time to pass through

    the distance of uncertainty. 

    7.5.2 Checking my progress

    1. The idea of uncertainty is used in many contexts; social, economic
    and scientific. People often talk about uncertain times, and when you
    perform a measurement you should always estimate the uncertainty
    (sometimes called the error). In physics the Heisenberg Uncertainty
    relation has a very specific meaning.

    a. Write down the Heisenberg uncertainty relation for position and
    momentum.
    b. Explain its physical significance.
    c. Does the Heisenberg uncertainty principle need to be considered
    when calculating the uncertainties in a typical first year physics
    experiment? Why or why not?
    d. Discuss the following statement: the uncertainty principle places a
    limit on the accuracy with which a measurement can be made. Do
    you agree or disagree, and why?
    2. An electron is confined within a region of width 11 5 10 m − × (Roughly
    the Bohr radius)
    a. Estimate the minimum uncertainty in the component of the
    electron’s momentum.
    b. What is the kinetic energy of an electron with this magnitude of
    momentum? Express your answer in both joules and electron

    volts.

    7.6 MATTER AND ANTIMATTER (PAIR PRODUCTION AND
    ANNIHILATION)

    ACTIVITY 7.5: Describing the matter and antimatter

    Use internet to describe the following concepts:
    1. Matter and give examples of matter particles
    2. Antimatter and give examples of antimatter particles
    3. Pair production
    4. Annihilation

    7.6. 1 Introduction

    Matter is a substance that has mass and takes up a space by having a volume. This
    include atoms and anything made up of these but no other energy phenomena
    or wave such as light or sound. Everything around you is made up of matter
    and is composed of particles including the fundamental fermions (quarks, 
    leptons, antiquarks and antileptons) which generally are matter particles and

    antimatter particles.

    Antimatter is a material composed of the antiparticle to the corresponding
    particle or ordinary particles. In theory a particle and its antiparticle have the
    same mass as one another but opposite electric charge and other differences in
    quantum numbers. Neutrons have antineutrons, electrons have positrons and
    neutrons have antineutrons as their respective antimatter. It was once thought
    that matter would neither be created nor destroyed. We know that energy and

    mass are interchangeable.

    7.6.2 Pair production and annihilation

    Pair production is a crucial example that photon energy can convert into
    kinetic energy as well as rest mass energy. Schematic diagram about the process
    of pair production is shown in Fig.7.5. The high-energy photon that has energy
    hf loses its entire energy when it collides with nucleus. Then, it makes pair of

    electron and positron and gives kinetic energy to each particle.

    Annihilation: When a particle collides with its antiparticle, the two annihilate
    each other with their mass being entirely converted into energy by the process
    called ‘’Annihilation’

    These particles and anti-particles can meet each other and annihilate one
    another (See Fig.7.6). In each case the particle and its antiparticle annihilate
    each other, releasing a pair of high energy gamma photons.

    In this example, a proton and an anti-proton meet each other and annihilate,
    producing high energy gamma rays in the form of photons. Rest mass, charge,
    momentum and energy are conserved. They can also be produced from a high

    energy photon, this is called pair production.

    7.6.3 Application of antimatter
    Antimatter as a form of antiparticle of sub atomic particles has a variety of
    applications:
    • Positron emission tomography can be used to potentially treat cancer.
    • Stored antimatter can be used for interplanetary and inter stellar
    travel.
    • Antimatter reactions have practical applications in medical energy.
    • Antimatter has been considered as a trigger mechanism for nuclear
    weapons because whenever antimatter meets its corresponding
    matter the energy is released by annihilation.

    7.6.4 Checking my progress
    1. Antimatter as a form of sub atomic particles
    a. Electron
    b. proton
    c. matter
    d. antiparticle
    e. none of them is correct
    2. The process in which a particle and antiparticle unite annihilate each
    other and produce one or more photons is called………
    3. What happens when matter and antimatter collide?

    4. Compare matter and antimatter

    END UNIT ASSESSMENT 7
    A. Multiple choices
    1. The positron is called the antiparticle of electron, because it
    a. Has opposite charge and Annihilates with an electron
    b. Has the same mass
    c. Collides with an electron
    d. Annihilates with an electron
    2. Beta particles are
    e. Neutrons
    f. Protons
    g. Electrons
    h. Thermal neutrons
    3. If gravity is the weakest force, why is it the one we notice most?
    a. Our bodies are not sensitive to the other forces.
    b. The other forces act only within atoms and therefore have no
    effect on us.
    c. Gravity may be “very weak” but always attractive, and the
    Earth has enormous mass. The strong and weak nuclear
    forces have very short range. The electromagnetic force has a
    long range, but most matter is electrically neutral.
    d. At long distances, the gravitational force is actually stronger
    than the other forces.
    e. The other forces act only on elementary particles, not on
    objects our size.
    B. Structured questions
    4. According to the classification of elementary particles by mass.

    Complete the following figure

    5.
    I. State two differences between a proton and a positron.
    II. A narrow beam of protons and positrons travelling at the same
    speed enters a uniform magnetic field. The path of the positrons
    through the field is shown in Fig.7.7. Sketch on this figure the

    path you would expect the protons to take.

    III. Explain why protons take a different path to that of the
    positrons.
    6. A positron with kinetic energy 2.2 MeV and an electron at rest
    annihilate each other. Calculate the average energy of each of the
    two gamma photons produced as a result of this annihilation.
    C. Essay question
    7. Describe briefly the following particle-terms terms: π -meson,

    muon, neutrino, antiparticle, hadrons and lepton.

  • UNIT 8: PROPERTIES AND BASIC PRINCIPLES OF QUARKS

    Key unit competence: Organize the properties and basic principles of quarks.
    My goals
    • List types of quarks, identify quarks, antiquarks and hadrons (baryons
    and mesons)
    • Define baryon number and state the law of conservation of baryon
    number.
    • Interpret the baryon number and apply the law of conservation of
    baryon number
    • State colors of quarks and gluons.
    • Explain how color forms bound states of quarks.

    • Formulate the spin structure of hadrons (baryon and mesons) 

    INTRODUCTORY ACTIVITY

    In the study of matter description and energy as well as their interactions;
    the fascinating thing of discovery is the structure of universe of infinite size
    but still there is a taskto know the origin of matter. The smallest particle was
    defined to be electron, proton, and neutron. But one can ask:
    1. What particles are components of matter?

    2. Describe and discuss how particles interact with energy to form matter.

    8.1 INTRODUCTION
    ACTIVITY 8.1: Investigating about elementary particles
    Considering the knowledge and skills obtained from unit 8, about
    the study of elementary particles, discuss and explain the following
    questions:
    1. Discuss the major groups of elementary particles
    2. Explain and analyze the family of quarks and their interactions.

    3. Why should we learn about elementary particles?

    Particle physics is the field of natural science that pursues the ultimate
    structure of matter. This is possible in two ways. One is to look for elementary
    particles, the ultimate constituents of matter at their smallest scale, and the
    other is to clarify what interactions are acting among them to construct matter
    as we see them. The exploitable size of microscopic objects becomes smaller as
    technology develops. What was regarded as an elementary particle at one time
    is recognized as a structured object and relinquishes the title of “elementary
    particle” to more fundamental particles in the next era. This process has been

    repeated many times throughout the history of science (Nagashima, 2013).

    In the 19th century, when modern atomic theory was established, the exploitable
    size of the microscopic object was and the atom was “the elementary particle”.
    Then it was recognized as a structured object when J.J. Thomson extracted
    electrons in 1897 from matter in the form of cathode rays. Its real structure
    (the Rutherford model) was clarified by investigating the scattering pattern of

    α-particles striking a golden foil (See Fig 9.1). 

    In 1932, Chadwick discovered that the nucleus, the core of the atom, consisted
    of protons and neutrons. In the same year, Lawrence constructed the first
    cyclotron. In 1934 Fermi proposed a theory of weak interactions. In 1935
    Yukawa proposed the meson theory to explain the nuclear force acting among

    them.

    It is probably fair to say that the modern history of elementary particles began
    around this time. The protons and neutrons together with their companion
    pions, which are collectively called hadrons, were considered as elementary
    particles until 1960. We now know that they are composed of more fundamental
    particles, the quarks. Electrons remain elementary to this day. Muons and
    τ-leptons, which were found later, are nothing but heavy electrons, as far as the
    present technology can tell, and they are collectively dubbed leptons. Quarks
    and leptons are the fundamental building blocks of matter. The microscopic
    size that can be explored by modern technology is nearing The quarks
    and leptons are elementary at this level (Nagashima, 2013). Some composite

    particles as stated by (Hirsch, 2002) are summarized in the tables below

    8.1. Checking my progress

    1. Each hadron consists of a proper combination of a few elementary
    components called
    a. Photons.                                    c. Quarks.
    b. Vector bosons.                        d. Meson-baryon pairs.
    2. Which of the following is not conserved in a nuclear reaction?
    a. Nucleon number.                 c. Charge
    b. Baryon number.                   d. All of the above are
    c. Conserved.
    3. The first antiparticle found was the
    a. Positron.                                 c. Quark.
    b. Hyperon.                                d. Baryon.



    8.2 TYPES OF QUARKS
    ACTIVITY 9.2: Investigating Quark particles

    Use search internet and find the explanation about quarks and types of

    quarks

    Aquark is a type of elementary particle and a fundamental constituent of
    matter. Quarks combine to form composite particles called hadrons, the most
    stable of which are protons and neutrons, the components of atomic nuclei.
    Due to a phenomenon known as color confinement, quarks are never directly
    observed or found in isolation; they can be found only within hadrons, such as
    baryons (of which protons and neutrons are examples) and mesons. For this
    reason, much of what is known about quarks has been drawn from observations
    of the hadrons themselves (Douglass, PHYSICS, Principles with applications.,
    2014). 

    Quarks have various intrinsic properties, including electric charge, mass, color
    charge, and spin. Quarks are the only elementary particles in the Standard
    Model of particle physics to experience all four fundamental interactions,
    also known as fundamental forces (electromagnetism, gravitation, strong
    interaction, and weak interaction (see section 8.5), as well as the only known
    particles whose electric charges are not integer multiples of the elementary
    charge. There are six types of quarks, known as flavors: up, down, strange,
    charm, top, and bottom (see Fig. 8.2). Up and down quarks have the lowest

    masses of all quarks. 

    The heavier quarks rapidly change into up and down quarks through a process
    of particle decay (the transformation from a higher mass state to a lower mass
    state). Because of this, up and down quarks are generally stable and the most
    common in the universe, whereas strange, charm, bottom, and top quarks can
    only be produced in high energy collisions (such as those involving cosmic rays
    and in particle accelerators). For every quark flavor there is a corresponding
    type of antiparticle, known as an antiquark, that differs from the quark only in
    that some of its properties have equal magnitude but opposite sign (Nagashima,

    2013).



    8.2.1 Checking my progress

    1. A proton is made up of
    a. One up quark and two down quarks
    b. An up quark and down antiquark
    c. Two up quarks and a down quark
    d. Strange quark and an anti-strange quark
    2. Particles that are un affected by strong nuclear force are
    a. Protons                          c. Neutrons
    b. Leptons                        d. Bosons
    3. Particle which explains about mass of matter is called
    a. Higgs boson                c. Leptons
    b. Protons                        d. Neutrons
    4. Describe the types and the characteristics of the quarks as well as their
    interaction properties.

    8.3 BARYON NUMBER, LEPTON NUMBER AND THEIR LAWS OF

    CONSERVATION

    ACTIVITY 8.3: Investigating about particle numbers

    Use search internet and retrieve the meaning of the following property
    of elementary particles.
    • Baryon numbers and

    • Lepton numbers

    One of the important uses of high energy accelerators is to study the interactions
    of elementary particles with each other. As a means of ordering this sub-nuclear
    world, the conservation laws are indispensable. The law of conservation of
    energy, of momentum, of angular momentum, and of electric charge is found to

    hold precisely in all particle interactions.

    A study of particle interactions has revealed a number of new conservation laws
    which (just like the old ones) are ordering principles. They help to explain why
    some reactions occur and others do not. For example, the following reactions

    have never been found to occur:

    Even though charge, energy, and so on are conserved means an antiproton and 

     means the reaction does not occur). To understand why such a reaction does
    not occur, physicists hypothesized a new conservation law, the conservation

    of baryon number.

    Thus the law of conservation of baryon number states that: “Whenever a nuclear
    reaction or decay occurs, the sum of baryon numbers before the process must

    equal the sum of the baryon numbers after the process.”

    Baryon number is a generalization of nucleon number, which is conserved in
    nuclear reaction and decays. All nucleons are defined to have baryon number
    , and all antinucleons (antiprotons, antineutrons) have  . All
    other types of particles, such as photons, mesons, and electrons and other

    leptons have 

    The reaction (9.01) shown above does not conserve baryon number since the
    left side B = +1+1 = +2 , and the right-hand side has B = +1+1−1 = +1 On
    the other hand, the following reaction does conserve B and does occur if the

    incoming proton has sufficient energy 

    As indicated, on both sides of this equation. From these and other
    reactions, the conservation of baryon number has been established as basic

    principle of physics.

    Also useful are the conservation laws of the three lepton numbers, associated
    with weak interactions including decays, in ordinary decay, an electron or
    positron is emitted along with a neutrino or antineutrino. In a similar type of
    decay, a particle known as or mu meson, or muo, can be emitted instead of
    an electron. The muon seems to be much like an electron, except its mass is 
    207 times larger The neutrinothat accompanies an emitted
    electron is found to be different from the neutrinothat accompanies an

    emitted muon. Each of these neutrinos has an antiparticle

    The law of conservation of electron-lepton number states that: “The sum of the
    electron-lepton numbers before reaction or decay must equal the sum of the
    electron-lepton numbers after the reaction or decay.”

    In ordinary decay we have for example,, a second quantum number, muon 

    lepton number, is conserved. The and are assigned and and havewhereas other
    particles have, too is conserved in interaction and decays. Similarly assignment
    can be made for the tau lepton number associated with the Lepton and its

    neutrino,

    Keep in mind that antiparticles have not only opposite electric charge from

    their particles, but also opposite 

     For example, neutrino has B = 1 an antineutrion has B = −1while all the

    The particle predicted by Yukawa was discovered in cosmic rays by C.F Powell

    and G. Ochialini in 1947, and is called the π or pi meson, or simple called pion.

    The incident proton from the accelerator must have sufficient energy to produce
    the additional mass of the free pion. Baryon number conservation keeps the
    proton stable, since it forbids the decay of the proton to e.g. a 0 π and a + π each

    of which have baryon number of zero.

    8.3.1 Checking my progress


    8.4 SPIN STRUCTURES OF HADRONS (HADRONS AND MESONS)
    ACTIVITY 8.4: Investigating the structure of elementary particles
    1. Use search internet and find the structure of elementary particles:
    Hadrons and mesons.
    2. Discuss and explain your findings in a brief summary about

    structure of hadrons.

    There are hundreds of hadrons, on the other hand, and experiments indicate
    they do have an internal structure. In 1963, M. Gell-Mann and G. Zweig
    proposed that none of the hadrons, not even the proton and neutron, are
    more fundamental, point like entities called, somewhat whimsically, quarks.
    Today, the quark theory is well accepted, and quarks are considered the truly

    elementary particles, like leptons. The three quarks originally proposed we 

    labeled u, d, s and have the names up, down and strange. The theory today has

    six quarks, just as there are six leptons based on presumed symmetry in nature,

    The other three quarks are called charmed, bottom and top (see Fig.8.2). The
    theory names apply also to new properties of each (quantum numbers c, t, b)
    that distinguish the new quarks from the old quarks (see Table 9.1below), and

    which (like strangeness) are conserved in strong, but not weak, interactions. 

    Table 8. 1 Properties of Quarks (Antiquarks have opposite sign Q, B. S, c, b and t
    All hadrons are considered to be made up of combinations of quarks, and their
    properties are described by looking at their quark content. Mesons consist of
    quark-antiquark pair (See Table 8.2).

    For example, a + π meson is a ud combination: note that for the ud pair, 

    After the quark theory was proposed, physicists began looking for those
    fractionally charged particles, but direct detection has not been successful.
    Current models suggest that quarks may be so tightly bound together that they
    may not ever exist singly in the free State. But observations of very high energy
    electrons scattered off protons suggest that protons are indeed made up of

    constituents.

    Today, the truly elementary particles are considered to be the six quarks, the
    six leptons and the gauge bosons that carry the fundamental forces. See Table
    9.4 where the quarks and leptons are arranged in three “generations.” Ordinary
    matter-atoms made of protons, neutrons, and electrons are contained in the
    “first generation”. The others are thought to have existed in the very early
    universe, but are seen by us today at powerful accelerators or in cosmic rays.
    All of the hundreds of hadrons can be accounted for by combinations of the six

    quarks and six antiquarks.

    Note that the quarks and leptons are arranged into three generations each

    8.4.1 Checking my progress


    8.5 COLOR IN FORMING OF BOUND STATES OF QUARKS
    ACTIVITY 8.5: Investigating the bound state of an atom
    Take the case of an electronic configuration of hydrogen atom. Make
    the illustration and then contrast the interaction between electron and

    proton and bound state of elementary particles.

    8.5.1 Bound state of quarks
    In the hydrogen atom configuration, the proton is located at centre while
    electron moves around it at a speed of about 1% the speed of light. The proton

    is heavy while the electron is light (See Fig.8.3) 

    This is the simplest example of what physicists call a “bound state”. The word
    state” basically just meaning a thing that hangs around for a while, and the
    word “bound” meaning that it has components that are bound to each other, as

    spouses are bound in marriage.

    The inside of the proton itself is more like a commune packed full of single
    adults and children: pure chaos. It too is a bound state, but what it binds is
    not something as simple as a proton and an electron, as in hydrogen, or even a
    few dozen electrons to an atomic nucleus, as in more complicated atoms such
    as gold, but zillions (meaning “too many and too changeable to count usefully”)
    of lightweight particles called quarks, antiquarks and gluons. It is impossible
    to describe the proton’s structure simply, or draw simple pictures, because it’s
    highly disorganized. All the quarks and antiquarks and gluons (see Fig.8.4)
    inside are rushing around as fast as possible, at nearly the speed of light

    (Strassler, 2011).

    Fig.8. 4 Snapshot of a proton: Imagine all of the quarks (up, down, and strange:
    u, d, s), antiquarks (u, d, s with a bar on top), and gluons (g) zipping around near
    the speed of light, banging into each other, and appearing and disappearing
    (Strassler, 2011). You may have heard that a proton is made from three quarks
    but this is not true. In fact there are billions of gluons, antiquarks, and quarks

    in a proton.

    8.5.2 Color in forming of bound states of quarks.
    In the standard model of Quantum Chromodynamics (QCD) and the electroweak
    theory (Giancoli D. C., Physics: principals with application, 2005), not long after
    the quark theory was proposed, it was suggested that quarks have another
    property (or quality) called color, or ‘color charge’ (analogous to electric
    charge). The distinction between the six quarks (u, d, s, c, b, t) was referred to

    as flavors

    According to the theory, each of the flavors of quark can have three colors,
    usually designated red, green and blue. These are the three primary colors
    which, when added together in equal amounts, as on a TV screen, produce
    white. Note that the names ‘color’ and ‘flavor’ have nothing to do with our
    sense, but are purely whimsical as are other names, such as charm, in this new
    field.The antiquarks are colored antired, antigreen and antiblue. Baryons are
    made up of three quarks, one of each color. Mesons consist of quark-antiquark
    pair of a particular color and its anti color. Both baryons and mesons are thus

    colorless or white.

    Originally, the idea of quark color was proposed to preserve the Pauli exclusion
    principle. Not all particles obey the exclusion principle. Those that do, such
    as electrons, protons and neutrons, are called fermions. Those that don’t are
    called bosons. These two categories are distinguished also in their spin: bosons
    have integer spin (0, 1, etc) whereas fermions have half-integer spin, usual
    as for electrons and nucleons, but other fermions have spin 
    Matter is made up mainly of fermions, but the carriers of forces ( and 
    gluons) are all bosons. Quarks are fernions they have spin 2
    1 and therefore
    should obey the exclusion principle. Yet for three particular baryons (uuu, ddd,
    and sss), all three quarks would have the same quantum numbers, and at least
    two quarks have their spin in the same quantum numbers, and at least two

    quarks have their spin in the same direction (since there are only two choices, 

    This would seem to violate the exclusion principle; but if quarks have an
    additional quantum number (color), which is different for each quark, it would
    serve to distinguish them and allow the exclusion principle to hold. Although
    quark color, and the resulting threefold increase in the number of quarks, was
    originally an adhoc idea, it also served to bring the theory into better agreement
    with experiment, such as predicting the correct lifetime of the  π meson. The
    idea of color soon became a central feature of the theory as determining the

    force binding quarks together in hadron.

    8.5.3 Colour as component of quarks and gluons
    ACTIVITY 8.6: Investigating the origin of color

    When a metal like iron is heated red-hot, one can observe the change
    in color. As the energy increases, as the color changes. Use the same
    experiment and discuss on the following questions
    1. As the color changes in the metal, what are the scientific reasons
    behind that?
    2. Explain the matter −energy interaction and their consequences

    3. What is color in the field of elementary particles?

    The attractive interactions among quarks are mediated by massless spin
    bosons called gluons in much the same way that photons mediate the
     electromagnetic interaction or that pions mediated the nucleon–nucleon force in the

    old Yukawa theory (Nagashima, 2013).

    Particles were classified into two categories:

    Quarks and leptons have an intrinsic angular momentum called spin, equal to

    a half-integer ( ) of the basic unit and are labeled as fermions. Fermions obey
    the exclusion principle on which the Fermi-Dirac distribution function is based.
    This would seem to forbid a baryon having two or three quarks with the same
    flavor and same spin component. To avoid this difficulty, it is assumed that each
    quark comes in three varieties, which are called color: red, green, and blue. The
    exclusion principle applies separately to each color. Particles that have zero or
    integer spin are called bosons. Bosons do not obey the exclusion principle and
    have a different distribution function, the Bose-Einstein distribution.
    • A baryon always contains one red, one green, and one blue quark, so
    the baryon itself has no net color.
    • Each gluon has a color–anticolor combination (for example, blue–
    antired) that allows it to transmit color when exchanged, and color is
    conserved during emission and absorption of a gluon by a quark.
    • The gluon-exchange process changes the colors of the quarks in such
    a way that there is always one quark of each color in every baryon.
    The color of an individual quark changes continually as gluons are

    exchanged.

    Similar processes occur in mesons such as pions:
    • The quark–antiquark pairs of mesons have canceling color and
    anticolor (for example, blue and antiblue), so mesons also have no net
    color. Suppose a pion initially consists of a blue quark and an antiblue
    antiquark.
    • The blue quark can become a red quark by emitting a blue–antired

    virtual gluon. 

    The gluon is then absorbed by the antiblue antiquark, converting it to an antired
    antiquark (Fig. 8.8). Color is conserved in each emission and absorption,
    but a blue–antiblue pair has become a red–antired pair. Such changes occur
    continually, so we have to think of a pion as a superposition of three quantum

    states:

    • Blue–antiblue,
    • Green–antigreen, and

    • Red–antired.

    In terms of quarks and gluons, these mediating virtual mesons are quark–

    antiquark systems bound together by the exchange of gluons.

    Fig.8. 5 (a) A pion containing a blue quark and an antiblue antiquark. (b) The
    blue quark emits a blue–antired gluon, changing to a red quark. (c) The gluon is
    absorbed by the antiblue antiquark, which becomes an antired antiquark. The
    pion now consists of a red–antired quark–antiquark pair. The actual quantum
    state of the pion is an equal superposition of red–antired, green antigreen, and

    blue–antiblue pairs.

    8.5.4 Checking my progess
    1. Label the illustration below and analyze the interaction between its

    particles

    Define and describe the following key concept:
    I. Color charge:
    II. Gluons
    III. Quantum chromodynamics
    2. Which one of the following sets of color combinations is added in color
    vision in TV’?
    a. Red, green and blue                                           c. White. red and yellow
    b. Orange, back and violet                                   d. Yellow, green and blue
    3. What are the color composition of
    a. Gluons
    b. Meson

    c. Baryon

    END UNIT ASSESSMENT 8

    A. Multiple choices

    1. A proton is made up of
    a. One up quark and two down quarks
    b. An up quark and down antiquark
    c. Two up quarks and a down quark
    d. Strange quark and an antistrange quark

    2. Particles that are unaffected by strong nuclear force are
    a. Protons                                                 c. Neutrons
    b. Teptons                                                d. Bosons

    3. Particle which explains about mass of matter is called
    a. Higgs boson c. Protons
    b. Leptons d. Neutrons
    4. A conservation law that is not universal but applies only to certain
    kinds of interactions is conservation of:
    a. Lepton number                                            d. Charge
    b. Baryon number                                           e. Strangeness
    c. Spin
    5. In quantum electrodynamics (QED), electromagnetic forces are
    mediated by

    a. the interaction of electrons.
    b. hadrons.
    c. D. the weak nuclear interaction.
    d. action at a distance.
    e. E. the exchange of virtual photons.

    6. Conservation laws that describe events involving the elementary
    particles include the conservation of energy.
    a. All of these are correct.
    b. electric charge.
    c. baryon and lepton numbers.

    d. linear and angular momentum.

    7. The conservation law violated by the reaction is the
    conservation of
    a. Charge.
    b. Energy.
    c. Linear momentum.
    d. Lepton number and baryon number.
    e. Angular momentum.
    8. Particles that participate in the strong nuclear interaction are called
    a. Neutrinos
    b. Hadrons
    c. Leptons
    d. Electrons
    e. Photons
    B. Structured questions
    9. In the table cross-word below, find at least fifteen names associated to
    elementary particles. Among them, select ones that represents quarks,

    leptons or radiations.

    10.a. Making massive particles: Relatively massive particles like the proton
    and neutron are made of combinations of three quarks.

    I. What is the charge on the combination uuu?
    II. What is the charge on the combination uud?
    III. What is the charge on the combination udd?
    IV. What is the charge on the combination ddd? 

    b. There are four compound particles here

    I. Which combination has the right charge to be a proton?

    II. Which combination has the right charge to be a neutron?

    III. There is a particle called the  which has a charge of –1e. Which

    quark combination could be the

    IV. There is a particle called the  ∆++ which has a charge of + 2e. Which
    quark combination could be the  ∆− ?

    V. A neutron can be changed to a proton if one quark changes ‘flavour’.
    What change is needed? What charge must be carried away if this

    happens? 

    c. Making mesons

    Other, lighter ‘middle-weight’ particles called mesons can be made from
    pairs of quarks. But they have to be made from a special combination: a
    quark and an antiquark. There are now four particles to play with: Up
    quark u: charge +2/3 e, Down quark d: charge –1/3 e, Antiup quark

    charge –2/3 e. Antidown quark : charge + 1/3 e.

  • UNIT 9: EFFECT OF X-RAYS

    Key unit competence: BAnalyze and evaluate the effects of x-rays.
    My goals
    • Explain the production of X-rays
    • State the properties of X-rays.
    • Explain the origin and characteristic features of an x-ray spectrum.
    • Outline the applications of X-rays in medicine, industries, and scientific
    research
    • Solve problems involving accelerating potential and minimum
    wavelength of X-rays.
    • Recognize how the intensity and quality of X-rays can be controlled.
    • Appreciate the use of X-rays in medicine and industry 

    INTRODUCTORY ACTIVITY

    When a person goes to the hospital with pain in her/his chest, or with an
    internal fracture of the bone, physicians do normally recommend the patient
    to pass by radiology service. Hence try to answer the following questions:
    1. Why do physicians recommend patients to pass by radiology service?
    2. Radiology means that there are radiations. Discuss different types of
    radiations that are found in there?
    3. Discuss the production of X-ray radiations.
    4. What are the positive and negative effects of X-ray radiation on the

    human body? 

    9.1 PRODUCTION OF X-RAYS AND THEIR PROPERTIES
    ACTIVITY 9.1: Investigating the production of X-rays

    Read the following text and answer the questions that follow.

    Discovery of X-rays: Becquerel’s discovery wasn’t the only important
    accidental one. In the previous year W.C. Roentgen unexpectedly
    discovered X-rays while studying the behavior of electrons in a
     high voltage vacuum tube. In that instance, a nearby material was made to

    fluoresce. Roentgen named them X- rays because he didn’t know what
    they were.

    Within twenty years of this discovery, diffraction patterns produced
    using X-rays on crystal structures had begun to show the finer structure
    of crystals while, at the same time, giving evidence that X-rays had a
    wave nature. Since then, X-ray radiation has become an indispensable
    imaging tool in medical science.

    Questions:
    1. What do you understand by X-rays?
    2. How are X-rays produced?

    3. Where are X-rays used?

    9.1.1 X-ray production

    X-rays are produced when fast moving electrons strike matter (see Fig.9.1).
    They were first produced in 1895 by Wilhelm Rontgen (1845-1923), using an

    apparatus similar in principle to the setup shown in Fig.9.1. 

    Electrons are emitted from the heated cathode by thermionic emission and are
    accelerated toward the anode (the target) by a large potential difference V. The
    bulb is evacuated (residual pressure  10−7  atm  or less), so that the electrons can
    travel from the cathode to the anode without colliding with air molecules. It
    was observed that when V is a few thousands volts or more, a very penetrating

    radiation is emitted from the anode surface.

    The above figure is an illustration of the Coolidge tube which is the most
    widely used device for the production of X-rays. The electrons are produced by
    thermionic effect from filament, which is the cathode of the tube, heated by an
    electric current. These electrons are accelerated towards a metal target that is

    the anode due to the high potential voltage between the cathode and the anode.

    The target metals are normally Tungsten or Molybdenum and are chosen
    because they have high melting point and higher atomic weights. The accelerated
    electrons interact with both electrons and nuclei of atoms in the target and
    a mysterious radiation is emitted. This radiation was referred to as X-rays.
    About 98% of the energy of the incident electron is converted into heat that is

    evacuated by the cooling system and the remaining 2% come out as X-rays.

    9.1.2 Types of X-rays

    Sometimes X-rays are classified according to their penetrating power. Two
    types are mentioned:
    Hard X-rays: those are X-rays on upper range of frequencies or
    shorter wavelength. They have greater energy and so they are more
    penetrating.
    Soft X-rays: they are X-rays on lower range of frequencies or
    longer wavelength. They have lower energy and they have very low
    penetrating power. The Fig.9.2 below shows the relative location of the

    different types of X-rays.

    Hard X-rays are produced by high accelerating potential. They have high
    penetrating power and short wavelength while soft X-rays are produced
    by lower accelerating potential, have relatively low penetrating power and

    relatively long wavelength.



    9.1.3 Properties of X-rays
    ACTIVITY 9.2: Understanding the pros and cons of X-rays
    Make intensive research on the production and the properties of
    X-rays, then write a report about your findings.

    The following are the main properties of X-rays:

    a. X-rays can penetrate through most substances. However, their penetrating
    power is different.
    b. X-ray can produce fluorescence in different substances.
    c. X-rays can blacken photographic plate. The degree of blackening depends
    upon the intensity of x-rays incident upon the plate. Thus, X-ray intensity
    can be measured with the help of photographic plates.
    d. X-rays ionize the gas through which they travel. The ionizing power
    depends on the intensity of the x-ray beam. Thus, X-ray intensity can also
    be measured by measuring their ionizing power.
    e. X-rays are not deflected by electric or magnetic fields. This proves that
    unlike cathode rays or positive rays they are not a beam of charged
    particles.
    f. X-rays travels on a straight lines like ordinary light.
    g. X-ray are both reflected and refracted.
    h. X-rays can be diffracted with the help of crystalline substances. They can

    also be polarized.

    From the above characteristics it can be seen that X-rays have the properties
    that are common to all electromagnetic radiations.

    9.1.4 Checking my progress

    1. Describe the process by which X-rays are produced.
    2. Discuss and describe the types of X-rays?
    3. What is the meaning of the X in X-ray?

    4. How are X-rays different from other electromagnetic radiations?

    9.2 THE ORIGINS AND CHARACTERISTIC FEATURES OF AN
    X-RAY SPECTRUM
    ACTIVITY 9.3: investigating the X-ray spectrum

    During the production of X-rays, a high voltage must be applied across
    the x rays tube to produce enough acceleration of electrons towards the
    target.
    Search internet, then discuss and explain the relationship between the

    applied

    9.2.1 Variation of the X-ray intensity with wavelength

    Depending on the accelerating voltage and the target element, we may find
    sharp peaks superimposed on a continuous spectrum as indicated on Fig.9.3.
    These peaks are at different wavelengths for different elements; they form what

    is called a characteristic x-ray spectrum for each target element.

    X-rays of different wavelengths are emitted from X-ray tube. If the intensity is
    measured as a function of the wavelength and the variation is plotted graphically 
    then a graph of the nature shown on the figure above is obtained.The graph has
    the following features:
    a. Minimum wavelength
    b. Continuous spectrum

    c. Characteristic peaks

    9.2.2 Origin of the continuous spectrum

    It is known that when charged particles such as electrons are accelerated or
    decelerated they emit electromagnetic radiation of different frequencies.
    In doing so a part of their kinetic energy is transformed in the energy of the
    emitted radiation. Electrons inside the x-ray tube decelerate upon hitting the
    target and as a result they emit electromagnetic radiations with a continuous
    distribution of wavelength starting from a certain minimum wavelength. This
    mechanism of producing electromagnetic radiation from an accelerated or

    decelerated electron is called bremsstrahlung.

    The energy of the emitted photon is given by

    The maximum energy of the emitted photons is therefore equal to the energy

    of the incident electron:

    Where   is the minimum wavelength, V is the potential difference between
    anode and cathode and e the charge of the electron.

    If V is measured in volts we get

    As the many electrons in the X-ray are decelerated differently, this will result in

    a continuous spectrum of the emitted wavelengths.

    It can be observed from the above Fig.9.4 that, for different values of the
    accelerating voltage, the minimum wavelength decreases with increasing
    potential difference and for a given wavelength the intensity is higher when the

    potential difference is higher.

    9.2.3 Origin of characteristic lines

    The peaks observed in wavelengths distribution curves as shown in Fig. 9.4
    are spectral lines in the X-ray region. Their origin lies in the transition between
    energy levels in the atoms of the target.The electrons in the atoms are arranged
    in different atomic shell. Of these, the first two electrons occupy the K-shell
    followed by 8 electrons in the L-shell, 18 electrons in the M-shell and so on
    until the electron in the target are used up. A highly accelerated electron may
    penetrate atom in the target and collide with an electron in K-shell. If such
    electron is knocked out it will leave an empty space that is immediately filled
    up by another electron probably from the L-shell or M-shell. This transition

    will be accompanied by the emission of the excess energy as a photon. 

    The energy of the emitted photon is a characteristic of the energy levels in the

    particular atom and is given by  

    For a transition between K and L-shells.
    Thus the energy of the emitted photon depends on the binding energies in the
    K and L shells and hence the x-ray spectral lines have definite frequencies and
    wavelengths which are characteristic of the target atom.
    For a given target material more than one spectral lines are observed as

    transitions may occur between different energy levels. 

    The X-ray lines originating from the transition between the different electron
    levels are usually labelled by the symbols α, β, γ, etc.
    From L-level to K-level transition produces Kα-line
    From M-level to K-level transition produces Kβ
     –line
    From M-level to L-level transition produces Lα –line
    From N-level to L- level transition produces  –line

    9.2.4 Checking my progress


    1. What is the characteristic of X-ray characteristic peak radiation?
    2. How is X-ray continuum produced via bremsstrahlung?
    3. X-rays are generated when a highly accelerated charged particle such
    aselectrons collide with target material of an X-ray tube. The resulting
    X-rays have two characteristics: the continuous X-rays (also called white
    X-rays) and characteristic X-rays peaks. The wavelength distribution and
    intensity of continuous X-rays are usually depending upon the applied
    voltage and a clear limit is recognized on the short wavelength side.
    a. Estimate the speed of electron before collision when applied voltage is
    30kV and compare it with the speed of light in vacuum.
    b. In addition, establish the expression of the shortest wavelength limit
    λmin of X-rays generated with the applied voltage V. it is obtained when

    the incident electron loses all its energy in a single collision.

    9.3 APPLICATIONS AND DANGERS OF X-RAYS
    ACTIVITY 9.4: investigating the X-ray uses and dangers

    1. Using the historical background of X-ray discovery, what are the
    uses of X-rays in real life?
    2. Discuss the dangers that X-rays may cause when they are used in a

    wrong way.

    X-rays have many practical applications in medicine and industry. Because X-ray
    photons are of such high energy, they can penetrate several centimetres of solid
    matter. Hence they can be used to visualize the interiors of materials that are

    opaque to ordinary light, such as broken bones or defects in structural steel. 

    9.3.1 In medicine

    X-ray imaging utilizes the ability of high frequency electromagnetic waves to
    pass through soft parts of the human body largely unimpeded. For medical
    applications, parts of the human body are exposed to moderated X-rays
    intensity and images are produced in similar way as light on a photographic
    plate or digital recorder to produce a radiograph (See Fig.9.7). 

    By rotating both source and detector around the patient’s body a “slice” image
    can be produced in what is called computerized tomography (CT). Although CT
    scans expose the patient to higher doses of ionizing radiation the slice images

    produced make it possible to see the structures of the body in three dimensions.

    In 1895, the Dutch Wilhelm Roentgen (See Fig.9.8) discovered that light energy
    could be used to take photographs through substances such as paper, cloths
    and wood. Roentgen also discovered that this invisible form of light energy,
    called X-rays could be used to take the pictures of structures inside the body as

    shown in Fig. below. Bone tissue appears clearly on an X-rays.

    The object to be visualized is placed between an X-ray source and an electronic
    detector (like that used in a digital camera) or a piece of photographic film
    (Fig.9.8 or Fig.9.8B). The darker area in the recorded images by such a detector,
    the greater the radiation exposure. Bones are much more effective X-ray
    absorbers than soft tissue, so bones appear as light areas. A crack or air bubble

    allows greater transmission and shows as a dark area.

    A widely used and vastly improved x-ray technique is computed tomography;
    the corresponding instrument is called a CT scanner. The x-ray source produces
    a thin, fan-shaped beam that is detected on the opposite side of the subject by an
    array of several hundred detectors in a line. Each detector measures absorption
    along a thin line through the subject. The entire apparatus is rotated around
    the subject in the plane of the beam, and the changing photon-counting rates of
    the detectors are recorded digitally. A computer processes this information and
    reconstructs a picture of absorption over an entire cross section of the subject.

    In the middle 1970, CT (Computer Tomography) scanning machines were
    introduced in human medicine.

    X-rays are also used in the following:
    • Killing of cancerous cells
    • Radiography is also used in industry for examining potentially damaged
    machinery to ascertain the cause of damage and to verify castings or

    welded joints

    • X-rays are used to study the structure of crystals (crystallography).
    • When a handgun is fired, a cloud of gunshot residue (GSR) is ejected from
    the barrel. The x-ray emission spectrum of GSR includes characteristic
    peaks from lead (Pb), antimony (Sb), and barium (Ba). If a sample taken
    from a suspect’s skin or clothing has an x-ray emission spectrum with
    these characteristics, it indicates that the suspect recently fired a gun.

    9.3.2 Examining luggage cargo and security



    X-rays are being used in airports to examine luggage for weapons or bombs.
    Note that the metal detector that you walk through in the airport does not X-ray
    you. It uses magnetic waves to detect metal objects. X-rays are also being used

    to examine cargo luggage for illegal or dangerous material as in Fig.9.9.

    9.3.3 In industry



    They can be used to detect structural problems and cracks in metals
     that cannot be seen from the outside. X-rays are used on commercial airplanes, 
    bridges metals and pipe lines, to make sure there are no stress fractures 

    or other dangerous cracks in the material.

    9.3.4 In scientific research
    • X-ray diffraction provides one of the most important tools for examining
    the three-dimensional (3D) structure of biological macromolecules
    and cells.
    • They are also used in crystallography, where X-ray diffraction and
    scattered waves show the arrangement of atoms in the crystal.


    The array of spots formed on the film is called a Laue pattern and show the

    atom structure of the crystal. 

    9.3.5 Dangers of X-rays
    X rays cause damage to living tissues. As X-ray photons are absorbed
    in tissues, their energy breaks molecular bonds and creates highly
    reactive free radicals (such as neutral H and OH), which in turn can
    disturb the molecular structure of proteins and especially genetic
    material. Young and rapidly growing cells are particularly susceptible,
    which is why X-rays are useful for selective destruction of cancer cells.
    • Because X-rays can kill living cells, they must be used with extreme care.
    When improperly used they can cause severe burns, cancer, leukemia,
    and cataracts. They can speed aging, reduce immunity to disease, and
    bring about disastrous changes in the reproductive cells.
    • Lead screens, sheets of lead-impregnated rubber, and leaded glass are
    used to shield patients and technicians from undesired radiation.
    • The effect of X-ray radiations is cumulative. That is, many minor doses
    over a number of years is equivalent to a large dose at one time.
    • Unnecessary exposure to x-rays should be avoided. MRI (Magnetic
    Resonance Imaging) uses magnets and sound energy to form pictures
    of the internal organs without exposing patients to harmful X-rays.
    • When they are used in hospitals, the sources should be enclosed in
    lead shields.
    • A careful assessment of the balance between risks and benefits of

    radiation exposure is essential in each individual case.

    9.3.6 Safety precaution measures of dangers caused by X-rays

    Medical and dental X-rays are of very low intensity, so that the hazard is

    minimized. However, X-ray technicians who go frequently behind the lead
    shield while operating X-rays need to be protected because of the frequency
    of exposure. A person can receive many medical or dental X-rays in a year with
    very little risk of getting cancer from it. In fact, exposure to natural radiation

    such as cosmic rays from space poses a greater risk.

    The following are some of the precautions:

    i. Protective suits and wears such as gloves and eye glasses made of lead are
    used always when handling these radiations. These shields protect the
    workers from X-ray exposure.
    ii. Workers who operate equipment’s that use X-rays must wear special
    badges which detect the amount of radiation they are exposed to.
    iii. Food and drinks are not allowed in places where X-radiations are present.
    iv. Experiments that involve these radiations (X-rays) substances should be
    conducted in a room surrounded by thick concrete walls or lead shields.
    v. Equipment that use X-rays should be handled using remote-controlled

    mechanical arms from a safe distance.

    9.3.7 Checking my progress
    1. How do we create different X-ray images in medicine?
    2. What are the dangers that may be caused by using excessive dose of

    X-rays?

    9.4 PROBLEMS INVOLVING ACCELERATING POTENTIAL AND
    MINIMUM WAVELENGTH.
    9.4.1 Accelerating potential and minimum wavelength
    ACTIVITY 9.5: Calculation of accelerating potential in X-ray tube
    An x-rays tube operates at 30 kV and the current through it is 2.0 mA.
    Calculate:
    a. The electrical power output
    b. The number of electrons striking the target per second.
    c. The speed of the electrons when they hit the target

    d. The lower wavelength limit of the X-rays emitted.

    When a high voltage with several tens of kV is applied between two electrodes,
    the high-speed electrons with sufficient kinetic energy is drawn out from the
    cathode and collides with the anode. The electrons rapidly slow down and lose
    kinetic energy. Since the slowing down patterns(method of losing kinetic
    energy)varies with electrons, continuous X-rays with various wavelength
    are generated. When an electron loses all its energy in a single collision, the
    generated X-ray has the maximum energy (or the shortest wavelength 
    ). The value of the shortest wave length limit can be estimated from the
    accelerating voltage V between electrodes.

    Because X-rays are emitted by accelerated charges, x-rays are electromagnetic
    waves. Like light, X-rays are governed by quantum relationships in their
    interaction with matter. Thus, we can talk about X-ray photons or quanta, and
    the energy of an X-ray photon is related to its frequency and wavelength in the

    same way as for photons of light,



    Typical X-ray wavelengths are . X-ray wavelength can be
    measured quite precisely by crystal diffraction techniques. X-ray emission
    is the inverse of the photoelectric effect. In photoelectric emission there is a
    transformation of the energy of a photon into the kinetic energy of an electron,
    in X-ray production there is a transformation of the kinetic energy of an electron
    into energy of a photon. In X-ray production we usually neglect the work
    function of the target and the initial kinetic energy of the boiled off electrons
    because they are very small in comparison to the other energies.



    Bragg’s Law

    According to W. L. Bragg ( (Weseda, Mastubara, & Shinoda, 2011), X-ray
    diffraction can be viewed as a process that is similar to reflection from planes of
    atoms in the crystal. In Bragg’s construct, the planes in the crystal are exposed
    to a radiation source at a glancing angle θ and X rays are scattered with an angle
    of reflection also equal to θ. The incident and diffracted rays are in the same
    plane as the normal to the crystal planes (Fig.9. 4). 

    


    Constructive interference occurs only when the path difference between rays
    scattered from parallel crystal planes would be an integer number of wavelengths
    of the radiation. When the crystal planes are separated by a distance d, the path
    length difference would be 2dsin θ. Thus, for constructive interference to occur

    the following relation must hold true. 

    The above derivation assumes that phase differences between wavelengths
    scattered at different points depend only on path differences. It is assumed that
    there is no intrinsic phase change between the incident and scattered beams or
    that this phase change is constant for all scattering events.

    9.4.2 Checking my progress
    1. Calculate
    a. Strength of the electric field E,
    b. Force on the electron F,
    c. Acceleration a of electron, when a voltage of 10 kV is applied between
    two electrodes separated by an interval of 10 mm.
    2. Crystal diffraction experiment can be performed using X-rays, or
    electrons accelerated through appropriate voltage. Which probe has
    greater energy?(For quantitative comparison,take the wavelength of the
    probe equalto1Å, which is of theorderofinter- atomicspacinginthelattice)

    (me = 9.11×10−31kg).

    END UNIT ASSESSMENT 9



    a. There are two main components of this x-ray spectrum: a broad
    range of x-ray energies and a couple of sharp peaks. Explain how
    each of these arises.
    b. What is the origin of the cut-off wavelength λmin of the Fig.9.5 shown
    below? Why is it an important clue to the photon nature of x-rays?
    c. What would happen to the cut-off wavelength if the accelerating
    voltage was increased? What would happen to the characteristic
    peaks? Use a sketch to show how this spectrum would look if the
    accelerating voltage was increased.
    d. What would happen to the cut-off wavelength if the target was
    changed, keep the same accelerating voltage? What would happen
    to the characteristic peaks? Use a sketch to show how the spectrum
    would look if some other target material was used, but the
    accelerating voltage was kept the same.
    3. Electrons are accelerated from rest through a p.d of 10 kV in an x ray
    tube. Calculate:
    I. The resultant energy of the electrons in eV.

    II. The wavelength of the associated electron waves. 

    III. The maximum energy and the minimum wavelength of the x ray

    radiation generated (assume 

    (1.6 10 ,1.24 10 ) J m − − × × .

    4. Monochromatic X-ray of wavelength 10 1.2 ×−10 m   are incident on a crystal.
    The1st order diffraction maximum is observed at when the angle between
    the incident beam and the atomic plane is 120

    .What is the separation of the atomic planes responsible for the diffraction? 

    5. An x-ray operates at 30 kV and the current through it is 2.0 mA. Calculate:
    I. The electrical power output
    II. The number of electrons striking the target per second.
    III. The speed of the electrons when they hit the target
    IV. The lower wavelength limit of the x-rays emitted.

    6. An x-ray machine can accelerate electrons of energies . The
    shortest wavelength of the x- rays produced by the machine is found
    to beUse this information to estimate the value of the plank

    constant.

    7. The spacing between Principal planes of Nacl crystal is 0 2.82 A . It is found
    that the first order Bragg diffraction occurs at an angle of 100
    . What is the
    wavelength of the x rays?

    8. What is the kinetic energy of an electron with a de Broglie wavelength of
    0.1 nm. Through what p.d should it be accelerated to achieve this value?
    9. You have decided to build your own x-ray machine out of an old television
    set. The electrons in the TV set are accelerated through a potential difference
    of 20 kV. What will be the λmin for this accelerating potential?
    10. A tungsten target (Z = 74) is bombarded by electrons in an x-ray tube.
    The K, L, and M atomic x-ray energy levels for tungsten are -69.5, -11.3 and
    -2.30 keV, respectively.
    a. Why are the energy levels given as negative values?
    b. What is the minimum kinetic energy of the bombarding electrons
    that will permit the production of the characteristic Kα and Kβ
    lines of tungsten?
    c. What is the minimum value of the accelerating potential that will
    give electrons this minimum kinetic energy?
    d. What are the Kα and Kß wavelengths?
    11. Using the following illustration figure Fig.10.6, label each part marked by

    letter from A to H and explain the function of each part A, B, C, D, E, F and H.

  • UNIT 10: EFFECT OF LASER


    Key unit Competence: Analyze the applications of LASER.
    My goals
    • Define a laser beam
    • Explain the stimulated emission of light
    • Explain the spontaneous emission of light
    • Analyse the mechanism to produce LASER beam
    • Explain laser properties
    • Explain and describe monochromatic and coherent sources of light
    • Analyse a LASER light as a source of coherent light.
    • Explain the principle and uses of Laser.
    • Outline applications of LASER
    • Analyse applications and dangers of LASER beam

    • Analyse precautional measures of the negative effects of Laser.

    INTRODUCTORY ACTIVITY

    A man has tied all forms of advancements from traditional methods of solving
    problems to advanced methods by use of different technologies. Among
    other technological advancements, discovery of Laser that is a part of visible
    light under electromagnetic waves has had a great impact in solving many of
    our problems.
    a. What do you understand by Electromagnetic waves?
    b. Discuss at least four (4) characteristics of Electromagnetic waves
    c. In your own words, discuss how these electromagnetic waves are
    produced.
    d. Are all kinds of these electromagnetic waves have the same energy? If
    Yes why? If No, why not?
    e. Basing on what you know about these electromagnetic waves, what
    could be positive uses of these waves. Also discuss negative effects of
    electromagnetic waves.

    f. How are electromagnetic waves related to LASERS?

    10.1 CONCEPT OF LASER
    ACTIVITY 10.1
    a. From your own understanding, explain how a LASER light is
    produced.
    b. Does production, need source of energy like electricity. Explain
    your reasoning.
    c. In energy levels, particles are either in ground or excited states.
    Is laser formed when particles or electrons are in ground or

    excited states? Explain your reasoning.

    The acronym LASER stands for Light Amplifier by Stimulated Emission of
    Radiation. This expression means that the light is formed by stimulating a
    material’s electrons to give out the laser light or radiation.

    The laser is a device that uses the ability of some substances to absorb
    electromagnetic energy and re-radiate it, as a highly focused beam of
    monochromatic and synchronized wavelength radiation. In 1953 Charles H.
    Townes, with graduate students James P. and Herbert J., produced the first
    Microwave Amplifier by Stimulated Emission of Radiation (MASER), 
    as a device operating in the same way as a laser, but amplifying microwave
    radiations.

    This system could release stimulated emissions without falling to the ground
    state, and thus maintaining a population inversion. A laser is a device that
    emits light through a process of optical amplification based on the stimulated
    emission of electromagnetic radiation. That is, the laser is a light source that
    produces a beam of highly coherent and very nearly monochromatic light

    because of cooperative emission from many atoms. 

    10.1.1 Absorption, Spontaneous emission and Stimulated emission
    ACTIVITY 10.2
    1. Using scientific explanations, Explain the meaning of the following
    terms
    I. Absorption
    II. Stimulated emission
    III. Spontaneous emission
    2. Electrons can jump from excited to ground state; does it absorb or
    radiate energy. Explain your reasoning.
    3. Write an equation that would be used to calculate the energy radiated
    by an electron when it jumps from one energy level to another. Explain
    each term used in the equation.

    4. What do you understand by the term population inversion?

    a. Absorption
    During the process of absorption, a photon from the source is destroyed and

    the atom which was at the ground state is promoted to the excited state. 




    In normal cases the excited states are less populated than the ground state.

    b. Spontaneous emission.

    An atom or an electron can move from one energy level to another. A photon is
    released when an electron moves from a higher energy level to a lower energy
    level. The release of photon (a particle of light) is called spontaneous emission.

    At the excited state, an atom will drop to a lower level by emitting a photon
    of radiation in a process called spontaneous emission. It emits the photon
    spontaneously after an average time τ called the spontaneous lifetime of the
    level. This time depends on the atomic species; some levels have long lifetime
    measured in seconds, whereas others are relatively short on the order of
    nanoseconds or less. This lifetime determines the ability of the emitting atom

    to store energy and will affect the efficiency of sources.






    frequency as the atomic frequency, there is a finite probability that this wave
    will force the atom to undergo the transition E2 → E1 .

    In this case the energy difference between the two levels is emitted in the form
    of electromagnetic wave that adds to the incident one. This is the phenomenon
    of stimulated emission. There is a fundamental difference between the
    spontaneous and stimulated emission processes because in spontaneous
    emission one photon is emitted and in stimulated emission both incident and
    emitted photons are observed. 

    10.1.2 Laser principle

    The principle of operation remains the same though there is a wide range of
    lasers. Laser action occurs in three stages: photon absorption, spontaneous
    emission, and stimulated emission. The particle of the material, which undergoes
    the process of excitation, might be an atom, molecule, or ion depending on the
    laser material. This principle is based on the principle of stimulated emission of
    radiation, the theory that was discussed by Einstein in 1917.The whole concept
    was discussed in the previous section.

    The photon emitted during stimulated emission has the same energy as the
    incident photon and it is emitted in the same direction as the latter, thus, getting
    two coherent photons. If these two coherent photons are incident on other
    two atoms in E2, then it will result in emission of two more photons and hence
    four coherent photons of the same energy are emitted. The process continues

    leading to doubling of the present number of photons.


    If the process is made to go on chain, we ultimately can increase the intensity
    of coherent radiation enormously. In figure above, such amplification of the
    number of the coherent photons due to stimulated emission is shown.

    The necessary condition for this type of amplification of light intensity by
    stimulated emission of radiation is that number of atoms in the upper energy
    state E2 must be sufficiently increased.

    10.1.3 Population inversion

    Population inversion: This is the process of increasing excited electrons in
    higher energy levels. This is the redistribution of atomic energy levels that

    takes place in a system so that laser action can occur.


    There are different methods of achieving population inversion in atomic states
    that is essential requirement to produce laser beam.

    Normally, most of the atoms in a medium are in the ground state of energy E0
    .There are four different methods of making these atoms to excited states.


    i. Excitation with the help of photons. If the atoms are exposed to an
    electromagnetic radiation of high frequency, then there is selective
    absorption of energy and thus atoms are raised to excited state.
    ii. Excitation by electrons. This method is used in some gas lasers. Electrons
    are released from the atoms due to high voltage electric discharge
    through a gas. These electrons are then accelerated to high velocities
    due to high electric field inside a discharge tube. When they collide with

    neutral gas atoms, a fraction of these atoms are raised to excited state 
    e + X → X+ e  Where X is an atom in ground state and ∗ X is an atom in

    excited state
    iii. Inelastic collision between atoms. If a gas contains two different two
    different kinds of atoms X and Y, then during electric discharge through
    the gas some of the atoms are raised to excited state.


    iv. Excitation by chemical energy. Sometimes, an atom or a molecule can be a
    product of a chemical reaction and can be produced in its excited state. An
    example is hydrogen combining with fluorine to form hydrogen fluoride

    HF that is in excited state.

    10.1.4 Laser structure
    ACTIVITY 10.3

    1. From what you know about LASER, what could be the components
    of laser
    2. Are all parts on laser Light Similar? Explain your reasoning.



    In general case laser system consists of three important parts:
    Active medium
    or amplifying medium, the energy source referred to as the pump or pump

    source and the optical resonator consisting of mirrors or system of mirrors.

    Pumping Mechanism.

    Pumping is the process of supplying energy to the laser medium to excite to
    the upper energy levels. To have this mechanism, it depends on the existence of
    interactions between light from pump source to constituents of active medium.
    Usually, pump sources can be: electrical discharges, flash lamps, arc lamps,
    light from another laser, chemical reactions and even explosive devices. Most
    common lasers use electrical or optical pumping. The type of pump source used

    depends essentially on the gain medium.

    Active Medium

    The active medium is the major determining factor of the wavelength of
    operation, and other properties of the laser. The gain medium is excited by the
    pump source to produce a population inversion, and it is where the spontaneous
    and stimulated emission of photons take place, leading to the phenomenon of
    optical gain or amplification. The gain medium may be a solid crystal like a
    ruby, a liquid dye, gases like CO2 or He-Ne or semiconductors. The gain medium
    for some lasers like gas lasers is closed by a window under the Brewster’s angle

    to allow the beam to leave the laser tube. 

    Optical resonator or Optical cavity

    The optical resonator or optical cavity is a system of two parallel mirrors placed
    around the gain medium that provide reflection of the light beam. Light from
    the medium produced by the spontaneous emission is reflected by the mirrors 
    back into the medium where it may be amplified by the stimulated emission.
    Mirrors are required for most lasers to increase the circulating power within
    the cavity to the point where gains exceed losses, and to increase the rate of
    stimulated emission. One of the mirrors reflects essentially 100% of the light,
    while the other less than 100% and transmits the remainder. Mirrors can be
    plane, spherical or a combination of both. Here represented are the common

    cavities configuration that can be used:



    10.1.5 Checking my progress

    1. What do you understand by the term LASER?
    2. Write in full the acronym L.A.S.E.R
    3. In your own words, explain how laser light is produced.
    4. Explain the meaning of population inversion and discuss how an atom
    can be put into excited state.
    5. What is the energy of the laser light that propagates with a frequency
    of 1010 Hz in gaseous medium. (Given that the plank’s constant

    6. What are the three major components of laser?

    7. Using diagrams, explain all the types of optical cavity.

    10.2 PROPERTIES OF LASER LIGHT
    ACTIVITY 10.4

    a. Using the ideas about electromagnetic radiations, what are
    characteristics of laser light?
    b. Do you think all different kinds of laser light have the same
    properties? Give reasons to support your answer.

    The laser light is not like any other light emitted by usual sources found in

    nature. This special light emitted by the laser, has three properties according
    to its usefulness in many applications: Coherence, Monochromaticity and

    Collimation or Directionality.

    10.2.1 Coherence

    Coherence is the most interesting property of laser light. All photons
    emitted, are exactly in the same phase, they are all crest and valley at the
    same time. It is brought about by the mechanism of the laser itself in which
    photons are essentially copied.The good temporal coherence is essentially for
    Interferometry like in Holography. Coherence is not trivial and is brought about

    by the amplification mechanism of the laser.

    10.2.2 Monochromaticity

    Monochromaticity is the ability of the laser to produce light that is at one
    wavelength λ. It is a requirement for coherence since photons of different
    wavelengths cannot be coherent. When white light is dispersed through a
    prism, you note that it is composed of an infinite number of wavelengths of
    light covering the entire visible spectrum as well as into the UV and IR regions.
    However, no light source is perfectly monochromatic. Lasers tend to be relatively 
    monochromatic and this depends on the type of laser. Monochromatic output,
    or high frequency stability, is of great importance for lasers being used in

    Interferometry.

    10.2.3 Collimation or Directionality

    Collimation or directionality is the property of laser light that allows it to stay in
    one direction at the strait line, confined beam for large distances. This property
    makes it possible to use the laser as a level in construction or to pinpoint
    speeders on a highway. This highly directional laser light is determined by the

    mechanism of the laser itself.

    10.2.4 Checking my progress

    1. Choose the correct group of terms that are properties of laser light.

    a. Coherent, unpolarized, monochromatic, high divergence

    b. Monochromatic, low divergence, polarized, coherent

    c. Polychromatic, diffuse, coherent, focused

    d. Monochromatic, birefringent, nonpolarized, coherent

    2. Which of the following properties of laser light enables us to use it to

    measure distances with great precision?

    a. All the light waves emitted by the laser have the same direction

    b. The light waves are coherent

    c. The light waves are monochromatic

    d. The individual waves effectively work like a single wave with very

    large amplitude.

    3. Explain how coherence, monochromatic and collimation are

    interconnected.

    4. All light in laser light are produced and found to be in the same phase.

    How does this help in the formation of 3D images?

    5. Laser light can be used as a level. Which special feature that makes it be

    used

    10.2.4 Checking my progress

    1. Choose the correct group of terms that are properties of laser light.
    a. Coherent, unpolarized, monochromatic, high divergence
    b. Monochromatic, low divergence, polarized, coherent
    c. Polychromatic, diffuse, coherent, focused
    d. Monochromatic, birefringent, nonpolarized, coherent
    2. Which of the following properties of laser light enables us to use it to
    measure distances with great precision?
    a. All the light waves emitted by the laser have the same direction
    b. The light waves are coherent
    c. The light waves are monochromatic
    d. The individual waves effectively work like a single wave with very
    large amplitude.
    3. Explain how coherence, monochromatic and collimation are
    interconnected.
    4. All light in laser light are produced and found to be in the same phase.
    How does this help in the formation of 3D images?
    5. Laser light can be used as a level. Which special feature that makes it be
    used

    10.3 APPLICATIONS AND DANGERS OF MISUSE OF LASER
    10.3.1 Applications of lasers.

    ACTIVITY 10.5

    a. Having studied LASERS, where do you think in real life LASERS
    are helpful?
    b. From your experience, have you ever used LASER light?
    c. Other than using it by yourself, what are other places where laser

    light is applied

    There are many interesting uses for lasers, depending on the special characteristic
    being applied. Laser Diodes are used in a wide range of applications. Partial
    lists of those applications include:
    i. They are used in common consumer devices such as DVD players, bar code
    scanners; CD ROM drivers; laser disc and other optical storage drivers;
    laser printers and laser fax machines; sighting and alignment scopes;
    measurement equipment; free space communication systems; pump
    source for other lasers; high performance imagers; and typesetters. CD
    players have lasers. Light from the laser in CD player reflects off patterns
    on CD’s surface. The reflected light is converted to a sound wave.

    ii. Laser beams can be used in diverse fields of science and technology. Like
    in the control of motion of moving objects like aircrafts or missiles. This
    method thus makes it possible for a missile to hit a certain target.
    iii. Because of high directional property, lasers are used to measure distances
    accurately. A laser beam is sent and the time taken for it to be reflected
    back is measured. Using this idea, the distance can thus be measured.
    iv. Because laser beam can be focused into a small spot, it can thus be used
    to cut minute holes onto a material.
    v. The very high intensity of laser beam means that the amplitude of the 
    corresponding electromagnetic wave is very large. So it is possible to
    investigate the non linear optical properties of different materials with
    the help of laser light.
    vi. Lasers are also used in industry for cutting materials such as metal and
    cloths. and welding materials
    vii. Doctors use lasers for surgery and various skin treatments
    viii. They are used in military and law enforcement devices for marking targets
    and measuring range and speed.
    ix. Laser lighting displays use laser light as an entertainment medium.
    x. Lasers also have many important applications in scientific research .
    In a tabular way, we can have a summary of different types of lasers and their
    applications.

    The following are types of lasers and their Applications

    a. Gas Lasers:


    b. Solid State Lasers:








    10.3.2 Dangers of lasers
    ACTIVITY 10.6

    Laser light is used in many areas like industries, offices, airports and
    many other places. Do you think long exposure of laser light is harmful?
    1. Why do you think so?
    2. What makes these lasers harmful if mis-used? Give a scientific

    reasoning

    You should be careful when dealing with lasers, because they can have a negative
    impact when exposed to your body. Among other negative effects, some of them
    are discussed below .
    i. If directly exposed to our skin, it burns the skin
    ii. When absorbed by skin, Laser light reacts with body cells causing cancer.
    iii. Because of their high energy, it affects eyes if exposed to them
    iv. Lasers can affect cells of a human being. This leads to mutation

    Because of the negative effects of lasers, care must be taken to avoid all the

    risks of being affected by lasers.

    10.3.3 Precaution measures

    ACTIVITY 11.7


    a. Observe the picture above clearly. Using scientific reasoning
    explain why the people performing the activity above are putting
    on protective wear as shown.

    b. Building on what you have discussed in a) above, what precautional
    measures can you take to avoid negative effects of LASERS if at all

    you were working in a place exposed to them.

    The following are some of the measures one can take to avoid the negative
    effects of lasers.

    i. For any one working in places where there are incidences of being exposed
    to laser light, one should wear protective clothes, glasses and shoes so
    that there is no direct exposure of these radiations on to the body.
    ii. One should minimize the time of working with lasers.
    iii. Areas that are exposed to these radiations should be warning signs and
    labels so that one can be aware of places/areas where laser light is used.
    iv. Safe measures like Use of remote control should be used to avoid direct
    exposure of these radiations (LASER light).
    v. People should be given trainings on how to handle lasers.

    vi. There should also access restrictions to laboratories that use laser

    10.3.4 Checking my progress
    1. Discuss all the negative effects of laser light.
    2. Using vivid examples, explain how one can prevent him or herself of all
    dangers caused by laser light.
    3. We have seen that laser light is good and at the same time bad. Using
    your personal judgement, which side outweighs the other. Give scientific
    reasons.
    4. Depending on your judgement in (3) do you think man should continue

    using laser light?

    END UNIT ASSESSMENT 1
    A. Multiple choice
    Copy the questions below to your exercise and chose the best alternative
    that answers the question.
    1. What does the acronym LASER stand for?
    a. Light Absorption by Stimulated Emission of Radiation
    b. Light Amplification by Stimulated Emission of Radiation
    c. Light Alteration by Stimulated Emission of Radiation
    2. The acronym MASER stands for?
    a. Microwave Amplification by Stimulated Emission of Radiation
    b. Molecular Absorption by Stimulated Emission of Radiation
    c. Molecular Alteration by Stimulated Emission of Radiation
    d. Microwave amplification by Stimulated Emission of Radio
    waves
    3. What is one way to describe a Photon?
    a. Solid as a rock
    b. A wave packet
    c. A torpedo
    d. Electromagnetic wave of zero energy
    4. Which of the following determines the color of light?
    a. Its intensity
    b. Its wavelength
    c. Its source
    d. Some information missing
    5. Among the three examples of laser listed below, which one is
    considered “eye safe”?
    a. Laser bar-code scanners
    b. The excimer laser
    c. Communications lasers
    d. YAG
    6. Why are lasers used in fiber optic communications systems
    a. The government has mandated it
    b. They can be pulsed with high speed data
    c. They are very inexpensive

    d. They are not harmful


    7. Lasers are used in CDs and DVDs. What type of laser is used in these

    players?
    a. Semiconductor
    b. YAG
    c. Alexandrite

    d. All the above


    8. The best reason why lasers used in “Laser Printers” is

    a. They can be focused down to very small spot sizes for high
    resolution
    b. They are cheap
    c. They are impossible to damage
    d. They are locally available
    9. As wavelength gets longer, the laser light can be focused to…
    a. Larger spot sizes
    b. Smaller spot sizes
    c. Large and small spot sizes
    d. None of the above
    10. Among the following, which color of laser has the shortest wavelength?

    a. Yellow                                                 c. Blue

    b. Red                                                     d. Green

    11. What property of laser light is used to measure strain in roadways?

    a. Intensity

    b. Power

    c. Coherence

    d. All the above

    12. What is the type of laser used most widely in industrial materials

    processing applications?

    a. Dye Laser                                   c. YAG laser

    b. Ruby Laser                                d. Carbon Dioxide Laser

    13. Why are lasers used for cutting materials

    a. It never gets dull               d. It has a small “heat affected zone”

    b. Accuracy                              e. Smoother cuts

    c. Repeatability                      f. All of the above

    14. The Excimer laser produces light with what wavelength?

    a. Visible

    b. Ultraviolet

    c. Infrared

    d. All the above.

    15. Most lasers are electrically inefficient devices.

    a. True

    b. False

    16. Chemical lasers use………………. to produce their beams.
    a. Excessive amounts of electrical power
    b. Small amounts of electrical power
    c. No electrical power
    d. Other lasers
    17. What type of laser could cause skin cancer if not used properly?
    a. Red semiconductor laser c. Blue semiconductor
    b. Excimer laser d. YAG laser.


    B. Structured questions


    18.
    a. What do you understand by term LASER?
    b. Depending on the nature and what laser is made of, Laser is
    classified into different types. Discuss at least 5 types of lasers.
    19 The following are basic characteristics of laser light. With clear
    explanation, what does each imply as connected to laser light.
    a. Coherence
    b. Monochromaticity
    c. Collimation
    20. a. With the aid of diagram Explain the meaning of the following terms
    I. Spontaneous Absorption of light
    II. Stimulated Emission cause harm if mis-used In what ways is
    laser light harmful.
    III. Spontaneous Emission
    IV. Population inversion
    b. Laser light have been employed in different areas. This has helped
    man in solving different problems. What are some of the areas
    where laser light is employed.
    c. Though laser light is very important in different activities, it can

    also

  • UNIT 11: MEDICAL IMAGING

    Key unit Competence: Analyze the processes in medical imaging.
    Learning objectives:
    • Outline specific purposes of imaging techniques
    • Explain the effects of various imaging techniques for particular
    purposes.
    • Explain the basic functioning principles of major medical imaging
    techniques

    • Identify advantages and disadvantages of medical imaging techniques

    INTRODUCTORY ACTIVITY

    Investigation on the use of medical imaging techniques:


    Years ago, the only way to get information from inside of human bodies was
    through surgery. In modern medicine, medical imaging has undergone major
    advancements and this ability to obtain information about different parts of
    the human body has many useful clinical applications.
    Using information provided on the above pictures, answer to the following
    questions:

    1. Observe the image A, B, and C (Fig.12.1) and describe what is happening.
    2. Suggest the technique that is being used for each image?
    3. Explain the working principle of the mentioned techniques in question

    2?

    11.1 X-RAY IMAGING.
    11.1.1 Interaction of X-rays with matter.
    a. Introduction

    In unit 10, we learnt that X-rays are electromagnetic radiation produced by
    focusing a beam of high energy electron on a target material in x-ray tube. Since
    the major part of the energy of the electrons is converted into heat in the target
    (only about 1% will appear as X-rays), the target material should have a high
    melting point and good heat conduction ability. To get a high relative amount of
    X-ray energy, the anode material should be of high atomic number. Tungsten is
    the dominating anode material and is in modern X-ray tubes often mixed with

    Rhenium.

    In X-ray diagnostics, radiation that is partly transmitted through and partly
    absorbed in the irradiated object is utilized. An X-ray image shows the variations
    in transmission caused by structures in the object of varying thickness, density

    or atomic composition. 

    b. Attenuation and Absorption of X-rays

    There are principally two interaction processes that give rise to the x-ray
    attenuation (variation in photon transmission) through the patient which is
    the basis of X-ray imaging. These are photoelectric absorption and scattering

    processes.

    A photon which has experienced an interaction process has either been
    absorbed or has changed its energy and/or direction of motion. A photon that
    changes its direction of motion is called a scattered photon. For monoenergetic
    x-ray photons, the number of photons that experience such interactions and
    therefore removed from the primary beam when this is incident on a thin
    layer of material is proportional to the number of incident photons (N) and the

    thickness of the layer (dx) following the expression :

    where µ is a constant of proportionality called the linear attenuation coefficient.

    Integrating the above equation will result in 

    where is the initial number of photons in the incident beam.

    It can be seen that the incident beam photons (or the beam energy) is attenuated
    exponentially as the X-rays travel through the material. The different interaction
    processes involved, that are absorption, coherent and incoherent scattering
    and pair production, add their contributions to the total linear attenuation

    coefficient 

    where µa, µcoh, µincoh, and µp are the contributions to the attenuation from photoelectric absorption, coherent scattering, incoherent scattering and pair production.

    C. Contrast

    The contrast is a measure of the difference in radiation transmission or
    other parameters between two adjacent areas in a radiographic image.
    Contrast plays an important role in the ability of a radiologist to perceive

    image detail.

    where ε1and ε are energies of the monoenergetic X-ray photons per unit area
    reaching the detector and therefore absorbed in the detector without and
    with the contrasting detail respectively. In the case where the film is used as
    image receptor, the signal is obtained in terms of the optical density. The image
    contrast is then usually defined as the optical density difference beside and

    behind the contrasting detail. 

    In such situation where monoenergetic photons are considered and no scattered
    radiation is reaching the detector, the absorbed energy in the detector can be

    written as 

    Where d, is the thickness of the object with linear attenuation coefficient

    The energy through the contrasting detail can be expressed as 

    where ε0 is the energy absorbed in the detector with no object present, x is the
    thickness of the contrasting detail with its linear attenuation coefficient µ2

    Replacing equation 12.05 and 12.06 into equation 12.04 we obtain the contrast 



    The contrast is then proportional to the difference in the linear attenuation
    coefficients and the thickness of the contrasting detail. Therefore, when
    scattered radiation is neglected in the process, the contrast is independent of
    the thickness d of the object but also it does not depend on where in the object
    the contrasting detail is situated.

    The ability of conventional radiography to display a range of organs and
    structures may be enhanced by the use of various contrast materials, also
    known as contrast media. The most common contrast materials are based on
    barium or iodine. Barium and iodine are high atomic number materials that

    strongly absorb X-rays and are therefore seen as dense white on radiography.

    11.1.2 X-rays Imaging Techniques
    a. Conventional Radiography

    X-rays are able to pass through the human body and produce an image of internal
    structures. The resulting image is called a radiograph, more commonly known
    as an ‘X-ray’ or ‘plain film’. The common terms ‘chest X-ray’ and ‘abdomen X-ray’

    are widely accepted and abbreviated to CXR and AXR. 

    As a beam of X-rays passes through the human body, some of the X-rays photons
    are absorbed or scattered producing reduction or attenuation of the beam with

    the internal human structure acting as contrasting details. 

    Therefore tissues of high density and/or high atomic number cause more X-ray
    beam attenuation and are shown as lighter grey or white on radiographs. Less
    dense tissues and structures cause less attenuation of the X-ray beam, and
    appear darker on radiographs than tissues of higher density. The figure below

    shows the typical conventional radiograph of a human body

    Fig.11.6: The five principal radiographic densities. This radiograph of a benign
    lipoma (arrows) in a child’s thigh demonstrates the five basic radiographic
    densities: (1) air; (2) fat; (3) soft tissue; (4) bone; (5) metal. (David A Disle
    (2012) Imaging for students. Fourth Edition. (Page 1)) 
    Five principal densities are easily recognized on this plain radiograph due to
    the increase in their densities:
    1. Air/gas appears as black, e.g. lungs, bowel and stomach
    2. Fat is shown by dark grey, e.g. subcutaneous tissue layer, retroperitoneal
    fat
    3. Soft tissues/water appears as light grey, e.g. solid organs, heart, blood
    vessels, muscle and fluid-filled organs such as bladder
    4. Bone appears as off-white
    5. Contrast material/metal: bright white.
    In the past, X-ray films were processed in a darkroom or in freestanding
    daylight processors. In modern practice, radiographic images are produced
    digitally using one of two processes, computed radiography (CR) and digital
    radiography (DR).
    DR uses a detector screen containing silicon detectors that produce an electrical
    signal when exposed to X-rays. This signal is analyzed to produce a digital
    image. Digital images obtained by CR and DR are sent to viewing workstations
    for interpretation. Images may also be recorded on X-ray film for portability
    and remote viewing.



    The image given by a computer radiography may be reviewed and reported
    on a computer workstation. This allows various manipulations of images as
    well as application of functions such as measurements of length and angles
    measurements.

     The relative variance of the shadows depends upon the density of the materials
    within the object or body part. Dense, calcium – rich bone absorbs X-rays to a
    higher degree than soft tissues that permit more X-rays to pass through them,
    making X-rays very useful for capturing images of bone.

    In projection radiography, there is much room for adjusting the energy level of
    the X-rays depending on the relative densities of the tissues being imaged and
    also how deep through a body the waves must travel in order to achieve the

    imaging.

    • Images of bones (for instance, to examine a fracture or for diagnostic
    measures related to bone conditions like osteoarthritis or certain
    cancers) require high-energy X-rays because of the high density of
    bone.
    • Images of soft tissues like lungs, heart and breasts (both chest X-rays
    and mammography are very common diagnostic applications of X-rays)
    require relatively less energy from the X-rays in order to penetrate
    properly and achieve excellent images.
    • In order to achieve these different energies, technologists use X-ray
    generators of different voltages and equipped with anodes made of

    different metals.

    b. Mammography
    ACTIVITY 11.2
    One day a girl suffering from the breast tells her mother about the
    problem. And her mother advises her to go to the hospital to consult a
    doctor.
    a. Think of the problem that girl may have.
    b. Try to explain what may be the cause of that problem.
    c. If you are a doctor how can you detect such problem?
    d. Which advise can you give to other people who are not suffering
    fro

    e. m that problem in order to prevent it?

    Mammography is a specialized medical imaging that uses low-dose X-rays to
    investigate the internal structure of the breast. A mammography exam, called
    a mammogram, helps in the early detection and diagnosis of women’s breast
    diseases such as breast cancer before even experiencing any symptom. Below
    is a typical mammography test showing the presence of abnormal areas of

    density, mass, or calcification that may indicate the presence of cancer.

    Mammographysada) the breast is pressed between two plates x-rays are used
    to takes pictures of breast tissues,(b)photographic image of breast tissues, (c)
    Breast with cancer. A mammography unit is a rectangular box that houses the
    tube in which X-rays are produced. The unit is used exclusively for X-ray exams
    of the breast, with special accessories that allow only the breast to be exposed
    to the X-rays. Attached to the unit is a device that holds and compresses the

    breast and positions it so images can be obtained at different angles.

    In conventional film and digital mammography, a stationery X-ray tube
    captures an image from the side and an image from above the compressed breast. 

    Breast tomosynthesis, also called three-dimensional (3-D) mammography
    and digital breast tomosynthesis (DBT), is an advanced form of breast imaging
    where multiple images of the breast from different angles are captured and
    reconstructed (“synthesized”) into a three-dimensional image set. In this way,
    3-D breast imaging is similar to computed tomography (CT) imaging in which
    a series of thin “slices” are assembled together to create a 3-D reconstruction

    of the body.

    c. Computer tomography scan (ct scan)

    CT terminology

    In 1970s, a revolutionary new X-ray technique was developed called Computer
    tomography (CT), which produce an image of a slice through the body. The

    word tomography comes from the Greek: tomos =slice, graph= picture.)

    A computed tomography scan also known as CT scan, makes use of computer 
    processed combinations of many X-ray measurements taken from different
    angles to produce cross-sectional (tomographic) images (virtual “slices”) of
    specific areas of a scanned object, allowing the user to see inside the object
    without cutting it. Other terms include computed axial tomography (CAT scan)
    and computer aided tomography. The term “computed tomography” (CT) is
    often used to refer to X-ray CT, because it is the most commonly known form

    but many other types of CT exist.

    CT is an imaging technique whereby cross-sectional images are obtained with
    the use of X-rays. In CT scanning, the patient is passed through a rotating
    gantry that has an X-ray tube on one side and a set of detectors on the other.
    Information from the detectors is analysed by computer and displayed as a
    grey-scale image. Owing to the use of computer analysis, a much greater array

    of densities can be displayed than on conventional X-ray films.

    This allows accurate display of cross-sectional anatomy, differentiation of
    organs and pathology, and sensitivity to the presence of specific materials such
    as fat or calcium. As with plain radiography, high- density objects cause more
    attenuation of the X-ray beam and are therefore displayed as lighter grey than

    objects of lower density. 

    Principle behind of computer tomography scan (CT scan).

    Computer Tomography is shown in below figure: a thin collimated beam of
    X- ray(“ to collimate” means to “make straight”) passes through the body to a

    detector that measures the transmitted intensity. Measurements are made at 

    a large number of points as the source and detector are moved past the body

    together. The apparatus is rotated slightly about the body axis and again scanned;
    this is repeated at  1 intervals for  180 . The intensity of the transmitted beam for
    the many points of each scan, and for each angles, are sent to a computer that
    reconstructs the image of the slice. Note that the imaged slice is perpendicular
    to the long axis of the body. For this reason, CT is sometimes called computerize

    axial tomography.

    The use of single detector would require a few minutes for many scans needed
    to form a complete image. Much faster scanner use a fan beam in which passing
    through the entire cross section of the body are detected simultaneously by
    many detectors. The x-ray source and the detectors are rotated about the
    patient and an image requires only few seconds to be seen. This means that
    rays transmitted through the entire body are measured simultaneously at each
    angle where the source and detector rotate to take measurements at different

    angles. 

    CT images of internal organs, bones, soft tissue, and blood vessels provide 
    greater clarity and more details than conventional X-ray images, such as a chest

    X-Ray

    Function of CT scan
    • A motorized table moves the patient through a circular opening in the
    CT imaging system.
    • While the patient is inside the opening, an X-ray source and a detector
    assembly within the system rotate around the patient. A single rotation
    typically takes a second or less. During rotation the X-ray source
    produces a narrow, fan-shaped beam of X-rays that passes through a
    section of the patient’s body.
    • Detectors in rows opposite the X-ray source register the X-rays that
    pass through the patient’s body as a snapshot in the process of creating
    an image. Many different “snapshots” (at many angles through the
    patient) are collected during one complete rotation.
    • For each rotation of the X-ray source and detector assembly, the
    image data are sent to a computer to reconstruct all of the individual
    “snapshots” into one or multiple cross-sectional images (slices) of the

    internal organs and tissues.

    Note that, it is advisable to avoid unnecessary radiation exposure; a medically
    needed CT scan obtained with appropriate acquisition parameter has benefits

    that outweigh the radiation risks.

    11.1.3 Checking my progress
    1. Outline the advantage and disadvantages CT scan
    2. Explain the types of x-ray imaging used in mammography.
    3. In mammography exams, is the breast compression necessary? Why
    4. A beam of X-rays passes through the human body of tissues with
    different densities; explain the production of X-rays on less dense

    tissues?

    11.2 ULTRASONIC IMAGING
    11.2.1 Basics of Ultra sound and its production
    ACTIVITY 11.3

    1. Distinguish ultrasound from infrasound?
    2. Where do you think ultrasound may be applied in daily life?

    3. Advise on how ultrasound be used in medicine?

    Sound can refer to either an auditory sensation in the brain or the disturbance
    in a medium that causes this sensation. Hearing is the process by which the ear
    transforms sound vibrations into nerve impulses that are delivered to the brain
    and interpreted as sounds. Sound waves are produced when vibrating objects
    produce pressure pulses of vibrating air. The auditory system can distinguish

    different subjective aspects of a sound, such as its loudness and pitch.

    Pitch is the subjective perception of the frequency, which in turn is measured in
    cycles per second, or Hertz (Hz). The normal human audible range extends from
    about 20 Hz to 20 000 Hz, but the human ear is most sensitive to frequencies
    of 1 000 Hz to 4 000 Hz. Loudness is the perception of the intensity of sound,
    related to the pressure produced by sound waves on the tympanic membrane.
    The pressure level of sound is measured in decibels (dB), a unit for comparing
    the intensity of a given sound with a sound that is just perceptible to the normal
    human ear at a frequency in the range to which the ear is most sensitive. On the
    decibel scale, the range of human hearing extends from 0 dB, which represents
    the auditory threshold, to about 130 dB, the level at which sound becomes

    painful.

    11.2.2 Interaction of sound waves with different structure inside the body
    a. Introduction

    Ultrasound imaging uses ultra-high-frequency sound waves to produce cross sectional
    images of the body. Ultrasound is actually sound with a frequency in

    excess of 20 kHz, which is the upper limit of human hearing. Typical ultrasound

    frequencies used for clinical purposes are in the 2 MHz to 10 MHz range.

    Different tissues in a human or animal body alter the ultra sound waves in
    different ways. Some waves are reflected directly while others scatter the
    waves before they return to the transducer as echoes. The reflected ultrasound
    pulses detected by the transducer need to be amplified in the scanner or
    ultrasonic probe. The echoes that come from deep within the body are more
    attenuated than those from the more superficial parts and therefore required

    more amplification.

    When echoes return to the transducer, it is possible to reconstruct a two
    dimensional map of all the tissues that have been in the beams. The information
    is stored in a computer and displayed on a video (television) monitor. Strong
    echoes are said to be of the high intensity and appear as brighter dots on the

    screen.

    b. Reflection of ultrasound 

    When the pulse of ultrasound is sent into the body and meets a boundary between
    two media, of different specific acoustic impedance Z, the sound wave needs to
    change gear in order to continue. If the difference in Z across the boundary is
    large the wave cannot easily adjust: there is an “acoustic mismatch”. Most of
    the wave is reflected and a strong echo is recorded. The fraction of intensity
    reflected back to that incident at the normal incidence, is known as the 

    intensity of reflection coefficient



    where Z is acoustic impedance
    Note that large difference in Z give rise to large values for α, producing strong

    echoes



    Ultrasounds are high-frequency sound waves above the human ear’s audible
    range: that is with frequency sound waves greater than 20 kHz. In fact, the
    frequencies used in medicine are much higher than this, typically between
    1 MHz and 15 MHz. like all sound waves, ultrasound consists of longitudinal,
    elastic or pressure waves, capable of traveling through solids, liquids and gases.

    This makes them ideal for penetrating the body, unlike transverse mechanical 

    waves, which cannot travel to any great extent through fluids.

    c. Attenuation of ultrasound

    The attenuation of the waves describes the reduction in its intensity as they
    travel through a medium. This loss is due to a number of factors:
    • The wave simply “spreads out” and suffers an “inverse square law type”
    reduction in intensity.
    • The wave is scattered away from its original direction
    • The wave is absorbed in the medium.
    The amount of absorption of ultrasound beam in a medium is described by the
    absorption coefficientα , which is intensity level per unit length. It is expressed
    in decibels per cm and it firstly depends on the type of medium the wave is
    propagating into. As example whilst water absorbs very little ultrasound,
    bone is a strong absorber, putting it at risk, for example, during high- power

    ultrasound therapy.

    Secondly, higher frequencies suffer greater absorption. In fact if the frequency is
    doubled, the absorption increases by the factor of four. This has very important
    consequences when choosing the best frequency at which to image the body. If
    the selected frequency is too high, the ultrasound will not be able to penetrate

    to the regions under investigation.

    11.2.3 Ultrasonic imaging techniques

    The basic component of the ultrasound probe is the piezoelectric crystal.
    Excitation of this crystal by electrical signals causes it to emit ultra-high frequency
     sound waves; this is the piezoelectric effect. The emitted ultrasound

    waves are reflected back to the crystal by the various tissues of the body. These
    reflected sound waves also called the “echoes” act on the piezoelectric crystal
    in the ultrasound probe to produce an electric signal, again by the piezoelectric

    effect. It is this electric signal which is analysed by a computer produces a cross sectional image.

    The process of imaging is the same as the echo-locating sonar of a submarine
    or a bat. The observer sends out a brief pulse of ultrasound and waits for an
    echo. The pulse travels out, reflects off the target and returns. The ultrasound
    machine uses pulses because the same device acts as both transmitter and
    receiver. If it continually sent out sounds, then the receiver would not hear the

    much softer echo over the louder transmission. 

    The duty cycle of the ultrasound imager is the amount of time spent transmitting

    compared to the total time of transmitting and listening.

    Sonar is an acronym for Sound Navigation and Ranging. It relies on the
    reflection of ultrasound pulses. A short pulse of ultrasound is directed towards
    the object interest, which then reflects it back as an echo. The total time
     between transmission of pulse and reception of an echo is measured, often
    using a cathode ray oscilloscope (CRO). The sonar principle is used to estimate

    the depth of a structure, using

    Where t is the time taken to go and back and v is the velocity of ultrasound in
    the medium.
    The factor of 2 is necessary because the pulse must travel “there and back”
    An ultrasound beam structure is directly into the body. The reflection or
    echoes from different body structure are then detected and analyzed, yielding
    information about the locations. For example if the time delays between the
    reception of echo pulse1 and 2 (Fig.11.12 below) is t , then the diameter of the

    baby’s head can be found using the above formula.

    During an investigation using ultrasound, the time delay for an echo to return
    from a structure is 10.5µs If the average velocity of ultrasound in the eye is 1510

    m/s. Calculate the depth of the structure. 

    a. Doppler ultrasonic

    An object travelling towards the listener causes sound waves to be compressed
    giving a higher frequency; an object travelling away from the listener gives a
    lower frequency. The Doppler effect has been applied to ultrasound imaging.
    Flowing blood causes an alteration to the frequency of sound waves returning
    to the ultra sound probe. This frequency change or shift is calculated allowing
    quantization of blood flow. The combination of conventional two-dimensional

    ultra sound imaging with Doppler ultra sound is known as Duplex ultra sound.

    The Doppler sample gate is positioned in the artery (arrow) and the frequency
    shifts displayed as a graph. Peak systolic and end diastolic velocities are

    calculated and also displayed on the image in centimeters per second.

    As ultrasound imaging uses sound waves to produce pictures of inside of the
    body. It is used to help diagnose the cause of pain, swelling and infection in
    the body’s internal organs and to examine a baby in pregnant woman and the
    brain and hips in infants. It is also used to help guide biopsies, diagnose heart

    conditions and assess damage after a heart attack.

    Ultrasound examinations do not use ionizing radiation (x-rays), there is no
    radiation exposure to the patient. Because ultrasound image are captured in
    real time, they can show the structure and movement of the body’s internal

    organs, as well as blood flowing through blood vessels.

    b. Advantages and Disadvantages of ultrasounds
     The advantages of ultrasound over other imaging modalities include:
    • Lack of ionizing radiation.
    • Relatively low cost
    • It is noninvasive (of medicine procedures not involving the introduction
    of instruments into the body)
    • Quick procedure
    • Good for examining soft tissues.

    • Portability of equipment.

    Some disadvantages of ultrasound include:
    • It is highly operator dependent as it relies on the operator to produce
    and interpret images at the time of examination
    • Not as much details as X-rays and MRI
    • It cannot be used in areas that contain gas (such as lungs)
    • Doesn’t pass through bones.

    • Can be wrong in detecting physical abnormalities.

    11.2.4 Checking my progress
    1. Explain how ultrasound imaging is used?
    2. Who take the decision to scan or not to scan in normal pregnancy?
    3. What are the risks and side effects to the mother or baby during
    ultrasound?
    4. If an ultrasound is done at 6 to 7 weeks and a heartbeat is not detected,

    does 

    11.3 SCINTIGRAPHY (NUCLEAR MEDICINE)
    ACTIVITY 11.4

    a. What do you understand by ‘radionuclide imaging’?
    b. What is a radionuclide scan used for?

    c. Compare radionuclide scan with mammography scan?

    11.3.1 Physics of scintigraphy and terminology

    Scintigraphy refers to the use of gamma radiation to form images following the
    injection of various radiopharmaceuticals. The key word to understanding of
    scintigraphy is radiopharmaceutical. ‘Radio’ refers to the radionuclide, i.e. the

    emitter of gamma rays. 

    The most commonly used radionuclide in clinical practice is technetium,
    written in this text as mTc 9 , where 99 is the atomic mass, and the ‘m’ stands for
    metastable. Metastable means that the technetium atom has two basic energy
    states: high and low energy states. As the technetium transforms from the highenergy state to the low-energy state, it emits a quantum of energy in the form of
    a gamma ray, which has energy of 140 keV. Other commonly used radionuclides

    include gallium citrate (67Ga), thallium (201TI), indium (111In) and iodine (  131 I).

    11.3.2 Basic functioning of radionuclide scan
    ACTIVITY 11.5

    For radionuclide imaging, it is advisable for the patient to consume a
    small quantity of radionuclide, or it is injected into a vein in your arm.
    a. How long does it take?
    b. What is the purpose of those radionuclide chemicals?
    c. Assuming the patient has already consumed the radionuclide for
    him/her to be scanned and wants to take another scan on another
    part of the body, will the patient be required to take another dose
    of the nuclide?
    d. You as a student, what advice can you give to a patient who

    develops allergies after taking the radio nuclear chemical? 

    A radionuclide scan is a way of imaging bones, organs and other parts of the
    body by using a small dose of a radioactive chemical. There are different types
    of radionuclide chemical. The one used depends on which organ or part of the

    body need to be scanned. 

    A radionuclide (sometimes called a radioisotope or isotope) is a chemical which
    emits a type of radioactivity called gamma rays. A tiny amount of radionuclide
    is put into the body, usually by an injection into a vein. Sometimes it is breathed

    in, or swallowed, or given as eye drops, depending on the test.

    Gamma rays are similar to X-rays and are detected by a device called a gamma
    camera. The gamma rays which are emitted from inside the body are detected
    by the gamma camera, are converted into an electrical signal and sent to a
    computer. The computer builds a picture by converting the differing intensities

    of radioactivity emitted into different colors or shades of grey.

    However, radionuclide imaging techniques do not depict structural anatomy like
    ultrasound, X-ray computed tomography (XCT) or conventional radiographs.
    It is the only established noninvasive technique available to investigate organ
    physiology, although recently Nuclear magnetic resonance (NMR) imaging
    technique has shown its capability to probe organ physiology and anatomy

    without ionizing radiation. 

    Radionuclide scans do not generally cause any after effects. Through the natural
    process of radioactive decay, the small amount of radioactive chemical in your
    body will lose its radioactivity over time. Although the levels of radiation used

    in the scan are small, patients may be advised to observe special precautions. 

    11.3.3 Limitations and disadvantages of scintigraphy
    The main advantages of scintigraphy are its high sensitivity and the fact that the
    functional information is provided as well as anatomical information. However
    it has some disadvantages that are listed below:
    i. Generally poor resolution compared with other imaging techniques.
    ii. Radiation risks due to the administered radionuclide
    iii. Can be invasive, sometimes requiring an injection into the bloodstream
    iv. Disposal for radioactive waste, including that from patients, requires
    special procedures.
    v. Relatively high costs associated with radiotracer production and

    administration.

    11.3.4 Checking my progress
    Choose the correct answers

    1. Scintigraphy refers to the use of:
    a. Gamma radiation to form images
    b. X- ray radiation to form images
    c. X- rays and gamma radiations to form images
    d. None of radiation to form images.
    2. The radionuclide in clinical practice are
    a. Technetium
    b. Thallium
    c. Gallium

    d. ALL of them

    11.4 MAGNETIC RESONANCE IMAGING (MRI)
    ACTIVITY 11.6:Principles of MRI

    1. What does MRI mean?
    2. What is it used for?
    3. What makes MRI to be powerful compared to other imaging
    techniques?
    4. is it advisable for a pregnant woman to be placed in MRI Scanner?

    Explain your view?

    11.4.1. MRI physics and terminology.

    Magnetic resonance (MR) imaging has become the dominant clinical imaging

    modality with widespread, primarily noninvasive, applicability throughout the
    body and across many disease processes. The progress of MR imaging has been
    rapid compared with other imaging technologies and it can be attributed in part
    to physics and in part to the timing of the development of MR imaging, which

    corresponded to an important period of advances in computing technology.

    Initially let us described how magnetic resonance can be demonstrated with
    a pair of magnets and a compass. If a compass happens to find itself near a
    powerful magnet, the compass needle will align with the field. In a normal
    pocket compass, the needle is embedded in liquid to dampen its oscillations.
    Without liquid, the needle will vibrate through the north direction for a period
    before coming to rest. The frequency of the oscillations depends on the magnetic

    field and of the strength of the magnetic needle.

    Let us focus on what made the needle oscillate. It was the small movements of
    the magnet, back and forth, or more precisely the oscillation of a weak magnetic
    field perpendicular to the powerful stationary magnetic field caused by the
    movement of the magnet. But oscillating magnetic field is what we understand
    by “radio waves”, which means that in reality, we could replace the weak magnet
    with other types of radio wave emitters. 

    This could, for example, be a small coil subject to an alternating current, as shown
    in figure above. Such a coil will create a magnetic field perpendicular to the
    magnetic needle. The field changes direction in synchrony with the oscillation
    of the alternating current, so if the frequency of the current is adjusted to the
    resonance frequency of the magnetic needle, the current will set the needle
    in motion. This is also applied in an MR scanner. In summary, the needle can
    be set in motion from a distance by either waving a magnet or by applying an
    alternating current to a coil. In both situations, magnetic resonance is achieved

    when the magnetic field that motion or alternating currents produce, oscillates
    at the resonance frequency. When the waving or the alternating current is
    stopped, the radio waves that are subsequently produced by the oscillating

    needle will induce a voltage over the coil. 

    MRI uses the magnetic properties of spinning hydrogen atoms to produce
    images. The first step in MRI is the application of a strong, external magnetic
    field. For this purpose, the patient is placed within a large powerful magnet.
    Most current medical MRI machines have field strengths of 1.5 or 3.0 Tesla.
    The hydrogen atoms within the patient align in a direction either parallel or

    antiparallel to the strong external field. 

    A greater proportion aligns in the parallel direction so that the net vector of
    their alignment, and therefore the net magnetic vector, will be in the direction
    of the external field. This is known as longitudinal magnetization. A second
    magnetic field is applied at right angles to the original external field. This second
    magnetic field is known as the radiofrequency pulse (RF pulse), because it is
    applied at a frequency in the same part of the electromagnetic spectrum as

    radio waves. A magnetic coil, known as the RF coil, applies the RF pulse.

    The RF pulse causes the net magnetization vector of the hydrogen atoms to
    turn towards the transverse plane, i.e. a plane at right angles to the direction
    of the original, strong external field. The component of the net magnetization
    vector in the transverse plane induces an electrical current in the RF coil. This
    current is known as the MR signal and is the basis for formation of an image.
    Computer analysis of the complex MR signal from the RF receiver coils is used
    to produce an MR image.
    11.4.2. The magnetism of the body
    Let‘s see how magnet needles with and without spin are affected by radio
    waves, we now turn to the “compass needles” in our own bodies.
    a. Most frequently, the MR signal is derived from hydrogen nuclei (meaning
    the atomic nuclei in the hydrogen atoms). Most of the body’s hydrogen is
    found in the water molecules. Few other nuclei are used for MR.
    b. Hydrogen nuclei (also called protons) behave as small compass needles
    that align themselves parallel to the field.
    c. The compass needles (the spins) are aligned in the field, but due to
    movements and nuclear interactions in the soup, the alignment only
    happens partially.
    d. The nuclei in the body move among each other (thermal motion) and the

    net magnetization in equilibrium is thus temperature dependent.

    e. Due to the number of hydrogen nuclei (about 1027  ) found in the body,
    the net magnetization still becomes measurable. It is proportional to the
    field: A large field produces a high degree of alignment and thus a large

    magnetization and better signal to noise ratio.

    11.4.3. Magnetic Resonance Imaging (MRI).

    In MRI, a particular type of nucleus is selected and its distribution in the body
    is monitored. Hydrogen is the most commonly imaged element, not only due to
    its abundance in the body but also because it gives the strongest MRI signals.
    The technique uses a very powerful magnet to align the nuclei of atoms inside
    the body, and a variable magnetic field that causes the atoms to resonate, a
    phenomenon called nuclear magnetic resonance. The nuclei produce their own
    rotating magnetic fields that a scanner detects and uses to create an image.
    MRI is used to diagnose a variety of disorders, such as strokes, tumors,
    aneurysms, spinal cord injuries, multiple sclerosis and eye or inner ear
    problems. It is also widely used in research to measure brain structure and

    function, among other things.


    An MRI scan can be used to examine almost any part of the body, including the:
    • Brain and spinal cord
    • Bones and joints
    • Breasts
    • Heart and blood vessels
    • Internal organs, such as the liver, womb or prostate gland ,etc

    The results of an MRI scan can be used to help diagnose conditions, plan

    treatments and assess how effective previous treatment has been.

    11.4.4. Functional of MRI Scan
    ACTIVITY 11.7

    a. Explain the function of MRI Scan.
    b. What are the advantages and disadvantages of MRI Scan?

    c. What are the hazards associated with MRI?

    There are many forms of MRI, some of them are:
    a. Diffusion-weighted imaging.
    Diffusion-weighted imaging (DWI) is sensitive to the random Brownian
    motion (diffusion) of water molecules within tissue. The greater the amount of
    diffusion, the greater the signal loss on DWI. Areas of reduced water molecule
    diffusion show on DWI as relatively high signal. Diffusion-weighted imaging
    is the most sensitive imaging test available for the diagnosis
    of acute
    cerebral infarction
    . With the onset of acute ischaemia and cell death there
    is increased intracellular water (cytotoxicoedema) with restricted diffusion
    of water molecules. An acute infarct therefore shows on DWI as an area of

    relatively high signal.

    b. Perfusion-weighted imaging

    In perfusion-weighted imaging (PWI) the brain is rapidly scanned following
    injection of a bolus of contrast material (gadolinium). The data obtained may
    be represented in a number of ways including maps of regional cerebral blood
    volume, cerebral blood flow, and mean transit time of the contrast bolus. PWI
    may be used in patients with cerebral infarct to map out areas of brain at risk of
    ischaemia that may be salvageable with thrombolysis.

    c. Magnetic resonance spectroscopy

    Magnetic resonance spectroscopy (MRS) uses different frequencies to identify
    certain molecules in a selected volume of tissue, known as a voxel. Following data
    analysis, a spectrographic graph of certain metabolites is drawn. Metabolites
    of interest include lipid, lactate, NAA (N-acetylaspartate), choline, creatinine,

    citrate and myoinositol. 

    Uses of MRS include characterization of metabolic brain disorders in children,
    imaging of dementias, differentiation of recurrent cerebral tumour from

    radiation necrosis, and diagnosis of prostatic carcinoma.

    d. Blood oxygen level-dependent imaging

    Blood oxygen level-dependent (BOLD) imaging is a non-invasive functional MRI
    (fMRI) technique used for localizing regional brain signal intensity changes in
    response to task performance. BOLD imaging depends on regional changes
    in concentration of deoxyhemoglobin, and is therefore a tool to investigate
    regional cerebral physiology in response to a variety of stimuli. BOLD fMRI may
    be used prior to surgery for brain tumor or arteriovenous malformation (AVM),

    as a prognostic indicator of the degree of postsurgical deficit.

    11.4.5 Advantage and disadvantages of MRI.
    Advantages of MRI in clinical practice include:
    1. Excellent soft tissue contrast and characterization
    2. Lack of ionizing radiation.
    3. Noninvasive machine.
    4. Lack of artefact from adjacent bones, e.g. pituitary fossa
    Disadvantages of MRI:
    1. High capital and running costs.
    2. Image selected and interpretation is complex.
    3. Examination can be difficult for some people who are claustrophobic
    4. The examination is noisy and takes long.
    5. Hazards with implants, particularly pacemakers.

    6. Practical problems associated with large superconducting magnets.

    11.4.7. Checking my progress

    1. What is meant by relaxation in the context of MRI?
    2. Give the reasons why the hydrogen nucleus is most used in MRI.
    3. What does NMR stand for? Explain carefully the role of the three terms
    involved

    4. Draw the basic steps in the formation of MRI image

    11.5 ENDOSCOPY
    ACTIVITY 11.8

    1. How can we examine inside the stomach by using light rays?

    2. How is endoscope performed? 

    11.3.1 Description

    Endoscopy is a nonsurgical procedure used to examine a person’s digestive tract.
    Using an endoscope, which is a flexible tube with a light and camera attached to
    it, the specialist can view pictures of your digestive tract on a monitor.
    During an upper endoscopy, an endoscope is easily passed through the mouth
    and throat and into the esophagus, allowing the specialist to view the esophagus,
    stomach, and upper part of the small intestine. Similarly, endoscopes can be
    passed into the large intestine (colon) through the rectum to examine this area
    of the intestine.

    11.3.2 Upper endoscopy

    Upper Endoscopy (also known as gastroscopy, EGD, or
    esophagogastroduodenoscopy) is a procedure that enables your surgeon
    to examine the lining of the esophagus (swallowing tube), stomach and
    duodenum (first portion of the small intestine). A bendable, lighted tube about
    the thickness of your little finger is placed through your mouth and into the

    stomach and duodenum.

    11.3.3. How is the upper endoscopy performed?

    Upper endoscopy is performed to evaluate symptoms of persistent upper

    abdominal pain, nausea, vomiting, difficulty swallowing or heartburn. It is an
    excellent method for finding the cause of bleeding from the upper gastrointestinal

    tract. It can be used to evaluate the esophagus or stomach after major surgery. 

    It is more accurate than X-rays for detecting inflammation, ulcers or tumors
    of the esophagus, stomach and duodenum. Upper endoscopy can detect early
    cancer and can distinguish between cancerous and noncancerous conditions

    by performing biopsies of suspicious areas.

    A variety of instruments can be passed through the endoscope that allows
    the surgeon to treat many abnormalities with little or no discomfort, remove
    swallowed objects, or treat upper gastrointestinal bleeding. Safe and effective
    control of bleeding has reduced the need for transfusions and surgery in many

    patients.

    11.3.4. Advantages and disadvantages of endoscopy
    Advantages

    • Complete visualization of the entire stomach or digestive tract.
    • It is very safe and effective tool in diagnosis
    • Does not leave any scar because it uses natural body openings.
    • It is cost effective and has low risk
    • They are generally painless.
    • Can do therapeutic interventions
    • Allows for sampling/biopsying of small bowel mucosa

    • Allows for resection of polyps.

    Disadvantages:
    • Although the endoscope is very safe; however, the procedure has a few
    potential complications which may include:
    • Bleeding
    • Perforation (tear in the gut wall)
    • Infection
    • Reaction to sedation (action of administering a sedative drug to
    produce a state of calm or sleep.
    • Technically difficult procedure
    • Very time consuming (Procedure can take > 3 hours)

    • Patient may need to be admitted to the hospital

    • Higher risk of small bowel perforation
    • Case reports of pancreatitis and intestinal necrosis

    • Reported incidents of aspiration and pneumonia

    11.3.5 Checking my progress
    1. What are instruments used to view the esophagus, stomach and upper
    small intestine of human body?
    2. Explain the function of endoscope.

    3. Compare and contrast colonoscopy and gastroscopy

    11.3.6. hazards associated with medical imaging
    The following are some hazards associated with medical imaging:
    1. Exposure to ionizing radiation
    2. Anaphylactoid reactions to iodinated contrast media
    3. Contrast-induced nephropathy (CIN)
    4. MRI safety issues

    5. Nephrogenic systemic sclerosis (NSF) due to Gd-containing contrast media

    1. Exposure to ionizing radiation

    Radiation effects and effective dose Radiography, scintigraphy and CT use
    ionizing radiation. Numerous studies have shown that ionizing radiation in
    large doses is harmful. The risks of harm from medical radiation are low, and
    are usually expressed as the increased risk of developing cancer as a result of
    exposure. Radiation effects occur as a result of damage to cells, including cell
    death and genetic damage. Actively dividing cells, such as are found in the bone

    marrow, lymph glands and gonads are particularly sensitive to radiation effects.

    2. Anaphylactoid contrast media reactions

    Most patients injected intravenously with iodinated contrast media experience

    normal transient phenomena, including a mild warm feeling plus an odd taste
    in the mouth. With modern iodinated contrast media, vomiting at the time of
    injection is uncommon. More significant adverse reactions to contrast media

    may be classified as mild, intermediate or severe anaphylactoid reactions:

    • Mild anaphylactoid reactions: mild urticaria and pruritis
    • Intermediate reactions: more severe urticaria, hypotension and mild
    bronchospasm
    • Severe reactions: more severe bronchospasm, laryngeal oedema,
    pulmonary oedema, unconsciousness, convulsions, pulmonary

    collapse and cardiac arrest.

    3. Contrast-induced nephropathy

    Contrast-induced nephropathy (CIN) refers to a reduction of renal function

    (defined as greater than 25 per cent increase in serum creatinine) occurring
    within 3 days of contrast medium injection. Risk factors for the development

    of CIN include: 

    Pre-existing impaired renal function, particularly diabetic nephropathy,
    Dehydration, Sepsis, Age>60 years, Recent organ transplant , Multiple myeloma.
    The risk of developing CIN may be reduced by the following measures:

     Risk factors should be identified by risk assessment questionnaire.

     Use of other imaging modalities in patients at risk including US or noncontrast-enhanced CT.

    • Use of minimum possible dose where contrast medium injection is
    required.
    • Adequate hydration before and after contrast medium injection.
    • Various pretreatments have been described, such as oral acetylcysteine;
    however, there is currently no convincing evidence that anything other

    than hydration is beneficial.

    4. MRI safety issues

    Potential hazards associated with MRI predominantly relate to the interaction
    of the magnetic fields with metallic materials and electronic devices.
    Ferromagnetic materials within the patient could possibly be moved by the
    magnetic field causing tissue damage. Common potential problems include
    metal fragments in the eye and various medical devices such as intracerebral
    aneurysm clips. Patients with a past history of penetrating eye injury are at risk
    for having metal fragments in the eye and should be screened prior to entering
    the MRI room with radiographs of the orbits. The presence of electrically active
    implants, such as cardiac pacemakers, cochlear implants and neurostimulators,
    is generally a contraindication to MRI unless the safety of an individual device

    is proven.

    5. Nephrogenic systemic sclerosis

    Nephrogenic systemic sclerosis (NSF) is a rare complication of some Gd-based
    contrast media in patients with renal failure. Onset of symptoms may occur
    from one day to three months following injection. Initial symptoms consist
    of pain, pruritis and erythema, usually in the legs. As NSF progresses there is
    thickening of skin and subcutaneous tissues, and fibrosis of internal organs
    including heart, liver and kidneys. Identifying patients at risk, including patients
    with known renal disease, diabetes, hypertension and recent organ transplant, 
    may reduce the risk of developing NSF following injection of Gd- based contrast
    media.
    Risk reduction in MRI
    A standard questionnaire to be completed by the patient prior to MRI should
    cover relevant factors such as:
    • Previous surgical history
    • Presence of metal foreign bodies including aneurysm clips, etc.
    • Presence of cochlear implants and cardiac pacemakers
    • Possible occupational exposure to metal fragments and history of
    penetrating eye injury
    • Previous allergic reaction to Gd-based contrast media

    • Known renal disease or other risk factors relevant to NSF.

    END UNIT ASSESSMENT 11
    Part I: Copy the following in your notebook and chose the correct answer
    1. Which are included in the system components of gamma rays camera for
    producing image of the body?
    a. Collimator
    b. Scintillation
    c. Attenuation
    d. All of the above
    2. Which of the following modalities does not use a form of ionizing
    radiation?
    a. Radiography.
    b. Computed tomography.
    c. Sonography.
    d. Magnetic resonance imaging
    3. Hazards not associated with modern medical imaging include:
    a. Anaphylactoid reactions to iodinated contrast media
    b. Complication of some Gd-based contrast media in patients with
    renal failure.
    c. Imaging of the breast improves a physician’s ability to detect small
    tumors
    d. Radiation effects and effective dose Radiography.
    4. Medical imaging systems are often evaluated the characteristics which
    are directly related to:
    a. Image noise.
    b. Image blurring.
    c. Image unsharpness.
    d. Visibility of anatomical detail.
    5. Risks associated with radionuclide imaging are:
    a. Generally poor resolution compared with other imaging modalities.
    b. Rarely receiving an overdose of chemical injected in the vein of the
    body.
    c. High capital and running costs

    d. None of them.

    Part II: Structured questions

    6. Write the missing word or words on the space before each number.
    The term ………………….. is often used to refer to X-ray CT.
    a. Gastroscopy is a procedure that enables your surgeon to examine the
    lining of the ………….
    b. The most sensitive imaging test available for the diagnosis of acute
    cerebral infarction is …………...
    c. Array of …………………. to transform the flashes into amplified electrical
    pulses inside the body.
    d. Transducers used are different depending on ………. of a patient, one
    has 5 MHz and other 3.5 MHz.
    e. Hydrogen nuclei (also called protons) behave as small …………… that
    align themselves parallel to the field.
    f. In ………………….. there are appearance three words: nuclear, magnetic
    and resonance.
    g. Examination can be ………………… is one of the disadvantages of MRI.
    7. Answer by True if it is True and by False if it is False
    a. The use of gamma radiation to form images following the injection of
    various radiopharmaceuticals is known as Scintigraphy.
    b. This decision to scan or not to scan a normal pregnancy must be made
    only by the photographer. There are universally accepted guidelines at
    present.
    c. Tissue in the body absorbs and scatters ultrasound in the same ways.
    Lower frequencies are more rapidly absorbed (attenuated) than higher
    frequencies.
    d. Upper endoscopy uses light and camera to view the esophagus, stomach,
    and upper part of the small intestine.
    e. Ultrasound is both generated and detected through high frequency
    oscillations in piezoelectric crystals so there is ionizing radiation
    exposure associated with ultrasound imaging.
    8. Compare endoscopy imaging and radionuclide imaging
    9. What are the advantages of MRI in clinical practice?
    10. Is ultrasound safe? explain.
    11. What areas of the body can be imaged by ultrasound?
    12. Why is ultrasound used in pregnancy?
    13. Explain the advantage of CT scan
    14. In mammography exams, is the breast compression necessary? Why
    Essay question
    Historically, MRI began in the central nervous system, but it is now extended to
    all regions of the human body. The excellent resolution and contrast available in
    any chosen plane in the body, makes the MRI an invaluable diagnostic tool with
    which to study body structure, function and chemistry, as well as disease. Discuss
    the application of MRI.


    

  • UNIT 12: RADIATIONS AND MEDICINE

    Key unit Competence: Analyze the use of radiation in medicine.

    My goals


    • Explain radiation dosimetry.

    • Differentiate the terms exposure, absorbed dose, quality factor (relative
    to biological effectiveness) and dose equivalent as used in radiation
    dosimetry.
    • Differentiate physical half-life, biological half-life and effective half-life
    • Solve radiation dosimetry problems
    • Analyse the basics of radiation therapy for cancer.
    • Explain safety precautions when handling radiations

    • Describe the concept of balanced risk.

    INTRODUCTORY ACTIVITY
    Radiation has always been present and is all around us. Life has evolved in
    a world containing significant levels of ionizing radiation. Our bodies are
    adapted to it.

    People are constantly exposed to small amounts of ionizing radiation from
    the environment as they carry out their normal daily activities; this is
    known as background radiation. We are also exposed through some medical
    treatments and through activities involving radioactive material.

    Fig 13.1 above identifies four major sources of public exposure to natural
    radiation: cosmic radiation, terrestrial radiation, inhalation and ingestion.
    Brainstorm and try to answer the following questions:

    a. Distinguish artificial source of radiation and natural source of radiation?
    b. Explain briefly each major source of public exposure to natural
    radiation stated above.
    c. Which kind of sources of radiation are mostly preferred to be used in
    medicine? Explain why
    d. Does exposure to heavy ions at the level that would occur during deep space
     missions of long duration pose a risk to the integrity and function

    of the central nervous system? Explain to support your idea.
    12.1 RADIATION DOSE
    12.1.1 Ionization and non-ionization radiations
    ACTIVITY 12.1:Types of radiation

    Radiation is the emission of particles or electromagnetic waves from a
    source. Radiation from radioactive materials has the ability to interact
    with atoms and molecules of living objects.
    a. With the help of the diagram below, distinguish the forms of
    radiation?
    b. Which type do you think is mostly used in medical treatment?
    Explain your answer with supporting arguments?
    c. Suggest the possible side effects of using radiations in medicine?
    Which of the two forms of radiation induces more side effects 
    when exposed to human body? Explain to support your choice.


    In a neutral atom, the positive charge of the nucleus is equal and opposite to the

    total negative charge of the orbital electrons. If such an atom loses or gains an
    electron, it becomes an ion. The atom will now have a net positive or negative
    charge and is called an ion. This process is called ionization, and the radiation
    responsible for it is called ionising radiation. When discussing the interaction
    of radiations with matter in particularly in relation to health, two basic types of

    radiation can be considered: 

    a. Ionizing radiation.

    This is a radiation that carries enough energy to liberate electrons from atoms
    or molecules, thereby ionizing them. As the more powerful form of radiation,
    ionizing radiation is more likely to damage tissue than non-ionizing radiation.
    The main source of exposure to ionizing radiation is the radiation used during

    medical exams such as X-ray radiography or computed tomography scans. 

    However, the amounts of radiation used are so small that the risk of any
    damaging effects is minimal. Even when radiotherapy is used to treat cancer,
    the amount of ionizing radiation used is so carefully controlled that the risk
    of problems associated with exposure is tiny. All forms of living things emit a
    certain amount of radiation, with humans, plants and animals accumulating
    radioisotopes as they ingest food, air and water. Some forms of radiation such as
    potassium-40 emit high-energy rays that can be detected using measurement
    systems. Together with the background radiation, these sources of internal

    radiation add to a person’s total radiation dose.

    Background radiation is emitted from both naturally occurring and man-made
    sources. Natural sources include cosmic radiation, radon radiation in the body,
    solar radiation and external terrestrial radiation. Man-made forms of radiation
    are used in cancer treatment, nuclear facilities and nuclear weapons. Globally, the
    average exposure to ionizing radiation per year is around 3 milliSieverts (mSv),
    with the main sources being natural (around 80%). The remaining exposure

    is due to man-made forms such as those used in medical imaging techniques. 

    Exposure to man-made forms of ionizing radiations is generally much higher
    in developed countries where the use of nuclear imaging techniques is much

    more common than in developing countries. 

    b. Non-ionizing radiations
    Non-ionizing radiation
    refers to any type of electromagnetic radiation that
    does not carry enough energy to ionize atoms or molecules. Examples of
    non-ionizing radiations include visible light, microwaves, ultraviolet (UV)
    radiation, infrared radiation, radio waves, radar waves, mobile phone signals
    and wireless internet connections. Although UV has been classified as a nonionizing
    radiation but it has been proven that high levels of UV-radiation can

    cause sunburn and increase the risk of skin cancer developing.

    Scientific investigations suggest that the use of telecommunications devices
    such as mobile phones may be damaging, but no risk associated with the use
    of these devices has yet been identified in any scientific studies. This energy

    is emitted both inside the body and externally, through both natural and manmade processes.

    12.1.2 Radiation penetration in body tissue
    ACTIVITY 12.2

    The figure below shows the penetrating power of radiation represented

    by A, B and C. Use the figure to answer the following questions.

    Questions:

    a. Interpret the figure and write the names of letters A, B and C
    labeled on the figure above?
    b. Which of the three types of radiation has high penetrating power?
    Explain to support your idea.
    c. Outline four uses of the man-made sources of radiation?
    d. How does radiation affect me? Explain clearly with scientific

    reasoning.

    An important characteristic of the various ionising radiations is how deeply
    they can penetrate the body tissues. X-rays, gamma rays, and neutrons of
    sufficient energy described below can reach all tissues of the body from an

    external source. 

    Alpha Radiation
    Alpha radiation
    occurs when an atom undergoes radioactive decay, giving
    off an α- particle consisting of two protons and two neutrons (essentially the

    nucleus of a helium-4 atom) following the equation

    Due to their charge and mass, alpha particles interact strongly with matter,
    and can only travel a few centimeters in air. A thin sheet of paper, on the other
    hand, stops alpha particles. They are also stopped by the superficial dead layer
    of skin that is only 70 µm thick. Therefore, radionuclides that emit only alpha
    particles are harmless unless you take them into the body. This you might do by

    inhalation (breathing in) or ingestion (eating and drinking).

    Beta Radiation

    Beta radiation takes the form of either an electron or a positron (a particle
    with the size and mass of an electron, but with a positive charge) being emitted
    from an atom. Due to their smaller mass, they are able to travel further in air,
    up to a few meters, and can be stopped by a thick piece of plastic, or even a
    stack of paper. Such radiation can penetrate the skin a few centimeters, posing
    somewhat of an external health risk. The depth to which beta particles can

    penetrate the body depends on their energy. 

    High-energy beta particles (several MeV) may penetrate a cm of a tissue,
    although most are absorbed in the first few mm. As a result, beta emitters
    outside the body are hazardous only to surface tissues such as the skin or the
    lenses of the eye. When you take beta emitters into the body, they will irradiate

    internal tissues and then become a much more serious hazard. 

    Gamma Radiation

    Gamma radiation, unlike alpha or beta, does not consist of any particles, instead

    consisting of a photon of energy being emitted from an unstable nucleus. Having
    no mass or charge, gamma radiation can travel much farther through air than
    alpha or beta, losing (on average) half its energy. Gamma waves can be stopped
    by a thick or dense enough layer material, with high atomic number. Materials

    such as lead can be used as the most effective form of shielding.

    X-Rays
    X-rays are similar to gamma radiation, with the primary difference being that
    they originate from the electron cloud. This is generally caused by energy
    changes in an electron, such as moving from a higher energy level to a lower
    one, causing the excess energy to be released. X-Rays are longer-wavelength

    and (usually) lower energy than gamma radiation, as well.

    Neutron Radiation

    Neutron radiation consists of a free neutron, usually emitted as a result of
    spontaneous or induced nuclear fission. They are able to travel hundreds or
    even thousands of meters in air, they are however able to be effectively stopped
    if blocked by a hydrogen material, such as concrete or water.

    Neutron radiation occurs when neutrons are ejected from the nucleus by
    nuclear fission and other processes. The nuclear chain reaction is an example
    of nuclear fission, where a neutron being ejected from one fission atom will
    cause another atom to fission, ejecting more neutrons. Unlike other radiations,
    neutron radiation is absorbed by materials with lots of hydrogen atoms, like

    paraffin wax and plastics.

    12.1.3 Radiation dosimetry
    ACTIVITY 12.3:

    a. What does the term Dosimeter in radiation dosimetry mean?
    b. Who Should Wear a Dosimeter? Suggest reasons why it is very important
    to wear a dosimeter?
    Just as for drugs, the effect of radiation depends on the amount a person has
    received. Therefore, amounts of radiation received are referred to as doses,

    and the measurement of such doses is known as dosimetry.

    Dosimeters are used to monitor your occupational dose from radioactive
    material or radiation-producing equipments. Most individuals working with
    X-ray producing equipment in the hospital will be issued with a dosimeter. For
    those individuals working in the research laboratory setting, dosimeters will
    be issued based on the nuclide and total activity that will be used. Dosimeters
    are integrating detectors; that is, they accumulate the radiation dose and give

    off an amount of light which is proportional to that dose.

    The energy absorption properties of dosimeters are designed to be very similar
    to tissue, so they are very effective as personnel dosimeters. These devices are
    used to measure exposures from x-ray, gamma ray and high energy beta
    particles
    . Dosimeters are not suitable for measuring exposures to low energy

    beta particles or alpha particles.

    12.1.4 Radiation exposure
    ACTIVITY 12.4:

    a. What are the symptoms of radiation exposure?
    b. Explain briefly the effects of radiation exposure to the human body?
    c. It is possible that side effects can happen when a person undergoes
    radiation treatment for cancer. Suggest the common side effects of
    radiation exposure to the human body?
    d. Does radiation exposure to the human body induce risks? Support your

    decision with clear explanations.

    Long-term exposure to small amounts of radiation can lead to gene mutations
    and increase the risk of cancer, while exposure to a large amount over a brief
    period can lead to radiation sickness

    Exposure is a measure of the ionization produced in air by X-rays or γ rays,
    and it is defined in the following manner. A beam of X-rays or γ rays is sent
    through a mass m of dry air at standard temperature and pressure ( stp:0 0C ,
    1 atm). In passing through the air, the beam produces positive ions whose total
    charge is q. Exposure is defined the total charge per unit mass of air.The SI unit

    for exposure is coulomb per unit mass (/ ) C kg .

    The commonly used unit for exposure E is the roentgen(R). 1R is the amount
    of electromagnetic radiation which produces in one gram of air

    C at normal temperature (22 and pressure (760mmHg) conditions

    Since the concept of exposure is defined in terms of the ionizing abilities of
    X-rays and γ rays in air, it does not specify the effect of radiation on living tissue.
    For biological purposes, the absorbed dose is more suitable quantity, because it
    is the energy absorbed from the radiation per unit mass of absorbing material.

    12.1.5 Absorbed radiation dose

    ACTIVITY 12.5

    a. What does the term absorbed dose mean in medical treatment?
    b. In the application of radiation in medicine, we use the statement “A measure of
    the risk of biological harm”. Brainstorm and explain clearly what the statement
    means.
    c. Explain why doses of alpha and gamma radiation produce unequal biological

    effects?

    What is important when we analyze the effect of radiation on human being is
    not so much the total dose to the whole system but the dose per kg. That’s why
    a doctor will prescribe smaller doses of medicine for children than for adults. A
    similar approach is used in radiation protection measurements, where the unit
    of absorbed dose is specified in terms of the amount of energy deposited by

    radiation in 1 kg of material. This unit is the Gray, abbreviated Gy. 

    It was named in honor of Louis Gray, who was a very big name in the early days
    of radiation dosimetry. An absorbed radiation dose of 1 Gray corresponds to
    the deposition of 1 joule of energy in 1 kg of material. The gray is a measure of
    energy absorbed by 1 kg of any material, be it air, water, tissue or whatever. A
    person who has absorbed a whole body dose of 1 Gy has absorbed one joule of

    energy in each kg of its body tissue. 

    As we shall see later, the gray is a fairly hefty dose, so for normal practical purposes

    we use the milligray (abbreviated mGy) and the microgray (abbreviated µGy). 

    The gray is a physical unit. It describes the physical effect of the incident
    radiation (i.e., the amount of energy deposited per kg), but it tells us nothing
    about the biological consequences of such energy deposition in tissue. Studies
    have shown that alpha and neutron radiation cause greater biological damage

    for a given energy deposition per kg of tissue than gamma radiation does. 

    In other words, equal doses of, say, alpha and gamma radiation produce unequal
    biological effects. This is because the body can more easily repair damage from
    radiation that is spread over a large area than that which is concentrated in a
    small area. Because more biological damage is caused for the same physical

    dose.

    12.1.6 Quality factors

    Quality factors are used to compare the biological effects from different types

    of radiation. For example, fast neutron radiation is considered to be 20 times
    as damaging as X-rays or gamma radiation. You can also think of fast neutron
    radiation as being of “higher quality”, since you need less absorbed dose to
    produce equivalent biological effects. This quality is expressed in terms of the
    Quality Factor (Q). The quality factor of a radiation type is defined as the ratio
    of the biological damage produced by the absorption of 1 Gy of that radiation to

    the biological damage produced by 1 Gy of X or gamma radiation. 

    The Q of a certain type of radiation is related to the density of the ion tracks it

    leaves behind it in tissue; the closer together the ion pairs, the higher the Q. 

    12.1.7 Equivalent dose

    The absorbed radiation dose, when multiplied by the Q of the radiation

    delivering the dose, will give us a measure of the biological effect of the dose.
    This is known as the equivalent dose. The unit of equivalent dose H is the Sievert
    (Sv). An equivalent dose of one Sievert represents that quantity of radiation
    dose that is equivalent, in terms of specified biological damage, to one gray of

    X or gamma rays. 

    In practice, we use the millisievert (mSv) and microsievert (µSv). The sievert is
    the unit that we use all the time, because it is the only one that is meaningful in
    terms of biological harm. In calculating the equivalent dose from several types
    of radiation (we call this “mixed radiation”), all measurements are converted to
    Sv, mSv or µSv and added. Most of the radiation instruments we use to measure
    doses or dose rates read in mSv or µSv. Few other instruments can read in mGy

    or µGy, but they measure only gamma radiation.

    The table 13.1 lists some typical relative biological effectiveness ( RBE ) values for
    different kinds of radiation, assuming that an average biological tissue is being
    irradiated. The values of 1 RBE = indicate that γ rays and particles produce
    the same biological damage as do 200 keV X-rays. The large RBE values indicate

    that protons, α -particles, and fast neutrons cause substantially more damage.

    12.1.8 Radiation protection

    The effects of radiation at high doses and dose rates are reasonably well
    documented. A very large dose delivered to the whole body over a short time
    will result in the death of the exposed person within days.

    We know from these that some of the health effects of exposure to radiation
    do not appear unless a certain quite large dose is absorbed. However, many
    other effects, especially cancers are readily detectable and occur more often in
    those with moderate doses. At lower doses and dose rates, there is a degree of
    recovery in cells and in tissues. Radiation protection sets examples for other
    safety disciplines in two unique respects:

    • First, there is the assumption that any increased level of radiation
    above natural background will carry some risk of harm to health.
    • Second, it aims to protect future generations from activities conducted

    today

    The use of radiation and nuclear techniques in medicine, industry, agriculture,
    energy and other scientific and technological fields has brought tremendous
    benefits to society. The benefits in medicine for diagnosis and treatment in
    terms of human lives saved are large in size. No human activity or practice
    is totally devoid of associated risks. Radiation should be viewed from the
    perspective that the benefit from it to mankind is less harmful than from many

    other agents.

    Quick check 12.2:

    At what level is radiation harmful? Explain your idea\

    Note: The optimization of patients’ protection is based on a principle that the
    dose to the irradiated target (tumor) must be as high as it is necessary for
    effective treatment while protecting the healthy tissues to the maximum extent

    possible. 

    12.1.9 Checking my progress

    1. Does receiving external-beam radiation make a person radioactive or
    able to expose others to radiation? Explain to support idea
    2. How can I be sure that the external-beam radiating machine isn’t
    damaging normal, healthy tissue in my body? Explain clearly with
    scientific reasoning.
    3. I am having an imaging test using radioactive materials. Will I be
    radioactive after the test? Comment to support your decision.
    4. All my radioactive material is secured properly and I have empty waste
    containers in the lab. Do I have to lock the room? Explain clearly to

    justify your decision.

    12.2 BIOLOGICAL EFFECTS OF RADIATION EXPOSURE
    12.2.1 Deterministic and stochastic effects
    ACTIVITY 12.6

    Is the use of ionizing radiation in medicine beneficial to human health?
    Explain to support your point.
    1. Are there risks to the use of ionizing radiation in medicine? Explain
    your answer.
    2. How do we quantify the amount of radiation?
    3. What do we know about the nature (mechanism) of radiation induced biological effects?
    4. How are effects of radiation classified?
    Effects of radiations due to cell killing have a practical threshold dose below
    which the effect is not evident but in general when the effect is present its
    severity increases with the radiation dose.
    The threshold doses are not an absolute number and vary somewhat by
    individual. Effects due to mutations (such as cancer) have a probability of
    occurrence that increases with dose.
    a. Deterministic effects:
    These effects are observed after large absorbed doses of radiation and are
    mainly a consequence of radiation induced cellular death. They occur only if a
    large proportion of cells in an irradiated tissue have been killed by radiation,
    and the loss can be compensated by increasing cellular proliferation.
    b. Stochastic effects:
    They are associated with long term, low level (chronic) exposure to radiation.
    They have no apparent threshold. The risk from exposure increases with
    increasing dose, but the severity of the effect is independent of the dose.
     Irradiated and surviving cells may become modified by induced mutations
    (somatic, hereditary). These modifications may lead to two clinically significant
    effects: malignant neoplasm (cancer) and hereditary mutations.
    The frequency or intensity of biological effects is dependent upon the total
    energy of radiation absorbed (in joules) per unit mass (in kg) of a sensitive
    tissues or organs. This quantity is called absorbed dose and is expressed in

    gray (Gy). 

    In evaluating biological effects of radiation after partial exposure of the body
    further factors such as the varying sensitivity of different tissues and absorbed
    doses to different organs have to be taken into consideration.

     To compare risks of partial and whole body irradiation at doses experienced
    in diagnostic radiology and nuclear medicine a quantity called equivalent or
    effective dose is used. A cancer caused by a small amount of radiation can be

    just as malignant as one caused by a high dose.

    ACTIVITY 12.7

    1. What is magnitude of the risk for cancer and hereditary effects?
    2. Is ionizing radiation from medical sources the only one to which
    people is exposed?
    3. What are typical doses from medical diagnostic procedures?
    4. Can radiation doses in diagnosis be managed without affecting the
    diagnostic benefit? Explain to support your decision.
    5. Are there situations when diagnostic radiological investigations
    should be avoided? Explain to support your decision.
    The lifetime value for the average person is roughly a 5% increase in fatal cancer
    after a whole body dose of 1 Sv. It appears that the risk in fetal life, in children
    and adolescents exceeds somewhat this average level (by a factor of 2 or 3) and
    in persons above the age of 60 it should be lower roughly by a factor of ~ 5.

    Animal models and knowledge of human genetics, the risk of hereditary
    deleterious effects have been estimated to not be greater than 10% of the
    radiation induced carcinogenic risk.

    All living organisms on this planet, including humans, are exposed to radiation
    from natural sources. An average yearly effective dose from natural background
    amounts to about 2.5 mSv. This exposure varies substantially geographically
    (from 1.5 to several tens of mSv in limited geographical areas).

    Various diagnostic radiology and nuclear medicine procedures cover a wide
    dose range based upon the procedure. Doses can be expressed either as
    absorbed dose to a single tissue or as effective dose to the entire body which
    facilitates comparison of doses to other radiation sources (such as natural
    background radiation.

    There are several ways to reduce the risks to very, very low levels while

    obtaining very beneficial health effects of radiological procedures.

    Quality assurance and quality control in diagnostic radiology and nuclear
    medicine play also a fundamental role in the provision of appropriate, sound

    radiological protection of the patient.

    There are several ways that will minimize the risk without sacrificing the
    valuable information that can be obtained for patients’ benefit. Among the
    possible measures it is necessary to justify the examination before referring a

    patient to the radiologist or nuclear medicine physician.

    Failure to provide adequate clinical information at referral may result in a
    wrong procedure or technique being chosen by radiologist or nuclear medicine

    specialist.

    An investigation may be seen as a useful one if its outcome - positive or negative
    influences management of the patient. Another factor, which potentially adds
    to usefulness of the investigation, is strengthening confidence in the diagnosis.
    Irradiation for legal reasons and for purposes of insurance should be carefully

    limited or excluded. 

    ACTIVITY 12.8


    1. Are there special diagnostic procedures that should have special
    justification? Explain to support your decision.
    2. Do children and pregnant women require special consideration in
    diagnostic procedures?
    3. What can be done to reduce radiation risk during the performance

    of a diagnostic procedure?

    While all medical uses of radiation should be justified, it stands to reason that
    the higher the dose and risk of a procedure, the more the medical practitioner
    should consider whether there is a greater benefit to be obtained.

    Among these special position is occupied by computed tomography (CT), and
    particularly its most advanced variants like spiral or multi slice CT.

    Both the fetus and children are thought to be more radiosensitive than adults.
    Diagnostic radiology and diagnostic nuclear medicine procedures (even in
    combination) are extremely unlikely to result in doses that cause malformations
    or a decrease in intellectual function. The main issue following in childhood
    exposure at typical diagnostic levels (<50 mGy) is cancer induction.

    Medically indicated diagnostic studies remote from the fetus (e.g. radiographs
    of the chest or extremities, ventilation/perfusion lung scan) can be safely done
    at any time of pregnancy if the equipment is in proper working order. Commonly
    the risk of not making the diagnosis is greater than the radiation risk.

    If an examination is typically at the high end of the diagnostic dose range and
    the fetus is in or near the radiation beam or source, care should be taken to
    minimize the dose to the fetus while still making the diagnosis. This can be
    done by tailoring the examination and examining each radiograph as it is taken
    until the diagnosis is achieved and then terminating the procedure

    For children, dose reduction in achieved by using technical factors specific for
    children and not using routine adult factors. In diagnostic radiology care should
    be taken to minimize the radiation beam to only the area of interest. Because
    children are small, in nuclear medicine the use of administered activity lower
    than that used for an adult will still result in acceptable images and reduced
    dose to the child. The most powerful tool for minimizing the risk is appropriate
    performance of the test and optimization of radiological protection of the
    patient. These are the responsibility of the radiologist or nuclear medicine
    physician and medical physicist.

    The basic principle of patients’ protection in radiological X-ray investigations
    and nuclear medicine diagnostics is that necessary diagnostic information of
    clinically satisfactory quality should be obtained at the expense of a dose as low
    as reasonably achievable, taking into account social and financial factors.

    12.2.2 Effects of radiation exposure

    Quick check13.1:
     Will small radiation doses hurt me?

    Some effects may occur immediately (days or months) while others might take
    tens of years or even get passed to the next generation. Effects of interest for
    the person being exposed to radiation are called somatic effects and effects of

    interest that affect our children are called genetic effects.

    I. Radiation Health Effects

    Ionizing radiation has sufficient energy to cause chemical changes in cells and
    damage them. Some cells may die or become abnormal, either temporarily or
    permanently. By damaging the genetic material (DNA) contained in the body’s
    cells, radiation can cause cancer.

    Fortunately, our bodies are extremely efficient at repairing cell damage. The
    extent of the damage to the cells depends upon the amount and duration of the

    exposure, as well as the organs exposed.

    Exposure to an amount of radiation all at once or from multiple exposures in a
    short period of time. In most cases, a large acute exposure to radiation causes
    both immediate ( radiation sickness) and delayed effects (cancer or death), can
    cause sickness or even death within hours or days. Such acute exposures are

    extremely rare.

    II. Chronic Exposure

    With chronic exposure, there is a delay between the exposure and the observed
    health effect. These effects can include cancer and other health outcomes such
    as benign tumors, cataracts, and potentially harmful genetic changes.

    Some radiation effects may occur immediately (days or months) while others
    might take years or even get passed to the next generation. Effects of interest
    for the person being exposed to radiation are called somatic effects and effects

    of interest that affect our children are called genetic effects

    ACTIVITY 12.9:Low levels of radiation exposure
    What is the safe level of radiation exposure? Explain your answer.
    What is the annual radiation exposure limit? Explain your answer

    Radiation risks refer to all excess cancers caused by radiation exposure
    (incidence risk) or only excess fatal cancers (mortality risk). Risk may be
    expressed as a percent, a fraction, or a decimal value.

    For example, a 1% excess risk of cancer incidence is the same as a 1 in a
    hundred (1/100) risk or a risk of 0.01. However, it is very hard to tell whether
    a particular cancer was caused by very low doses of radiation or by something
    else. While experts disagree over the exact definition and effects of “low dose”.
    Radiation protection standards are based on the premise that any radiation
    dose carries some risk, and that risk increases directly with dose.

    Note:
    • The risk of cancer from radiation also depends on age, sex, and factors
    such as tobacco use.
    • Doubling the dose doubles the risk.


    Acute health effects occur when large parts of the body are exposed to a

    large amount of radiation. The large exposure can occur all at once or from
    multiple exposures in a short period of time. Instances of acute effects from

    environmental sources are very rare. 

    12.2.3 Safety precautions for handling radiations
    ACTIVITY 12.10: Safety precautions to be recognized when
    handling radiation

    a. Who is involved in planning my radiation treatment?
    b. How is the treatment plan checked to make sure it is best for me?
    c. What procedures do I have in place so that the treatment team is
    able to treat me safely?
    d. How can I be assured that my treatment is being done correctly
    every day?
    e. What is the difference between a medical error and a side effect?
    f. Outline the measures taken to reduce doses from external

    exposure

    Shortening the time of exposure, increasing distance from a radiation source
    and shielding are the basic countermeasures (or protective measures) to reduce

    doses from external exposure.

    Note: Time: The less time that people are exposed to a radiation source, the less
    the absorbed dose Distance: The farther away that people are from a radiation

    source, the less the absorbed dose.

    Note: Shielding: Barriers of lead, concrete or water can stop radiation or reduce
    radiation intensity.

    There are four main factors that contribute to how much radiation a person
    absorbs from a source. The following factors can be controlled to minimize
    exposure to radiation:

    I. The distance from the source of radiation

    The intensity of radiation falls sharply with greater distance, as per the inverse
    square law. Increasing the distance of an individual from the source of radiation
    can therefore reduce the dose of radiation they are exposed to.
     For example, such distance increases can be achieved simply by using forceps
    to make contact with a radioactive source, rather than the fingers.

    II. Duration of exposure

    The time spent exposed to radiation should be limited as much as possible.
    The longer an individual is subjected to radiation, the larger the dose from the
    source will be.

      One example of how the time exposed to radiation and therefore radiation
    dose may be reduced is through improving training so that any operators who

    need to handle a radioactive source only do so for the minimum possible time.

    III. Reducing incorporation into the human body

    Potassium iodide can be given orally immediately after exposure to radiation.
    This helps protect the thyroid from the effects of ingesting radioactive iodine if
    an accident occurs at a nuclear power plant. Taking Potassium iodide in such an

    event can reduce the risk of thyroid cancer developing.

    IV. Shielding

    Shielding refers to the use of absorbent material to cover the source of
    radiation, so that less radiation is emitted in the environment where humans
    may be exposed to it. These biological shields vary in effectiveness, depending

    on the material’s cross-section for scattering and absorption. 

    The thickness (shielding strength) of the material is measured in g/cm2. Any
    amount of radiation that does penetrate the material falls exponentially with

    increasing thickness of the shield.

    Some examples of the steps taken to minimize the effects of radiation exposure
    are described below;
    • The exposed individual is removed from the source of radiation.
    • If radiation exposure has led to destruction of the bone marrow, the
    number of healthy white blood cells produced in the bone marrow will
    be depleted.
    • If only part of the body has been exposed to radiation rather than the
    whole body, treatment may be easier because humans can withstand

    radiation exposure in large amounts to non-vital body parts.

    In every medicine there is a little poison. If we use radiation safely, there are
    benefits and if we use radiation carelessly and high doses result, there are

    consequences. 

    Ionizing radiation can change the structure of the cells, sometimes creating
    potentially harmful effects that are more likely to cause changes in tissue.
    These changes can interfere with cellular processes so cells might not be able

    to divide or they might divide too much.

    Radioactive rays are penetrating and emit ionizing radiation in the form of
    electromagnetic waves or energetic particles and can therefore destroy living
    cells. Small doses of radiation over an extended period may cause cancer and
    eventually death. Strong doses can kill instantly. Marie Curie and Enrico Fermi

    died due to exposure to radiation.

     Several precautions should be observed while handling radioisotopes. Some of
    these are listed in the following:
    • No radioactive substance should be handled with bare hands. Alpha
    and beta emitters can be handled using thick gloves. Gamma ray
    emitters must be handled only by remote control that is by mechanical
    means. Gamma rays are the most dangerous and over exposure can
    lead to serious biological damage.
    • Radioactive materials must be stored in thick lead containers.
    • Reactor and laboratories dealing with and conducting experiments
    with radioactive metals must be surrounded with thick concrete lined
    with lead.
    • People working with radioactive isotopes must wear protective
    clothing which is left in the laboratory. The workers must be checked
    regularly with dosimeters, and appropriate measures should be taken
    in cases of overdose.

    • Radioactive waste must be sealed and buried deep in the ground.

    12.2.3 Checking my progress
    1.
    a. What does the term background radiation mean?
    b. Hat is radiation – am I exposed to background radiation each day
    even if I do not have an X-ray examination?
    2. What are the risks associated with radiation from diagnostic X-ray
    imaging and nuclear medicine procedures?
    3. How do I decide whether the risks are outweighed by the benefits of
    exposure to X-radiation when I have a radiology test or procedure?
    4. Are there alternatives to procedures that involve ionizing radiation that
    would answer my doctor’s question? Justify your answer with clear
    facts.
    5. What kinds of safety checks do you perform each day?
    6. How often does the medical physicist check the various machines
    involved during my treatment are working properly?
    7. If I have side effects after my treatment, who can I call?
    a. My best friend
    b. My primary care doctor
    8. I have a question about a radiation treatment I had many years ago.

    Who should I call?

    12.3 CONCEPT OF BALANCED RISK.
    12.3.1 Risks of ionizing radiation in medical treatment
    ACTIVITY 12.11:balanced risk

    Brainstorm and write briefly how balance risks in medical treatment
    occur?

    Risk in the area of radiation medicine has several dimensions that are less
    common in other areas of medicine. First, there may be risks
     from overexposure that do not cause immediate injury. For example, the causal connection,

    if any, may be difficult or impossible to verify for a malignancy that surfaces
    several years after an inappropriate exposure. Second, the risks associated
    with the medical use of ionizing radiation extend beyond the patient and can
    affect health care workers and the public.

    In amplifying these and other aspects of the risks that attend medical uses of

    ionizing radiation, the discussion addresses the following issues: human error 

    and unintended events; rates of misadministration in radiation medicine;
    inappropriate and unnecessary care; and efforts that reduce misadministration

    and inappropriate care.

    12.3.2 Human Error and Unintended Events

    Errors occur throughout health care: A pharmacist fills a prescription with the
    wrong medicine; an x-ray technician takes a film of the wrong leg; a surgeon
    replaces the wrong hip. The advent of complex medical technology has
    increased the opportunity for error even as it has increased the opportunity for
    effecting cures.

    By educating health care workers, and by circumscribing their actions, human
    error may be minimized. However, some number of mistakes will always,
    unavoidably, be made, and no amount of training or double-checking can erase

    that fact. 

    12.3.3 Comparison of risks in the use of ionizing radiation

    The comparison of relative risks of misadministration in by-product radiation
    medicine to error rates and events in other medical practice settings, as well
    as the comparison of disease and death rates with the risks of the therapeutic
    administration itself, help to some extent to place ionizing radiation use in a
    broader context.

    To achieve this success requires the highest standards of performance (accuracy
    of delivered dose), both when planning irradiation for an individual patient and
    in actual delivery of the dose.

    In a large number of cases, decreasing the dose to the target volume is not
    possible since it would unacceptably decrease the cure rate. In these cases
    present technological developments aim at optimizing the patients’ protection,
    keeping the absorbed tumor dose as high as is necessary for effective treatment
    while protecting nearby healthy tissues.

    It should be remembered that successful eradication of a malignant tumor by
    radiation therapy requires high-absorbed doses and there is a delayed (and
    usually low) risk of late complication. The above mention techniques are used
    to provide the best benefit/risk ratio.

    A malignant tumor in a pregnant woman may require radiotherapy in attempt
    to save life of the patient. If a tumor is located in a distant part of the body, the
    therapy with individually tailored protection of the abdomen (screening) - may
    proceed. 
    When thyroid cancer with metastases is diagnosed in a pregnant woman,
    treatment with 131I is not compatible with continuation of the pregnancy. The
    treatment should then be delayed until delivery if doing so wouldn’t put the
    mother’s life in danger.

    Medical radiation can be delivered to the patient from a radiation source
    outside the patient. Regardless of how much dose the patient received, they do
    not become radioactive or emit radiation. 

    • Balancing risks are often summarized in the following:
    • The demand for imaging, especially computed tomography, that has
    increased vastly over the past 20 years
    • An estimated 30% of computed tomography tests that may be
    unnecessary
    • Ionizing radiation that may be associated with cancer.
    • The risks of radiation exposure that is often overlooked and patients
    are seldom made aware of these risks
    • The requesting doctor who must balance the risks and benefits
    of any high radiation dose imaging test, adhering to guideline
    recommendations if possible
    • Difficult cases that should be discussed with a radiologist, ideally at a

    clinic radiological or multidisciplinary team meeting.

    12.3.4 Checking progress

    1. When patients are intentionally exposed to ionizing radiation for
    medical purposes, do they suffer unintentional exposures as a result of
    error or accident? Comment to support your idea.
    2. What can be done to reduce radiation risk during conduct of radiation
    therapy?
    3. Can pregnant women receive radiotherapy? Explain to support your
    decision.
    4. Can patients’ treatment with radiation affect other people? Explain to

    support your decision.

    12.4 THE HALF-LIVES: PHYSICAL, BIOLOGICAL, AND FFECTIVE
    ACTIVITY 12.12

    Distinguish between physical half-life, biological half-life and effective

    half-life.

    Brainstorm and write the distinction between physical half-life, biological half 

    life and effective half-life in your note books.

    The half-life is a characteristic property of each radioactive species and is
    independent of its amount or condition. The effective half-life of a given isotope
    is the time in which the quantity in the body will decrease to half as a result of

    both radioactive decay and biological elimination.

    There are three half-lives that are important when considering the use of
    radioactive drugs for both diagnostic and therapeutic purposes. While both
    the physical and biological half-lives are important since they relate directly
    to the disappearance of radioactivity from the body by two separate pathways
    (radioactive decay, biological clearance), there is no half-life as important in

    humans as the effective half-life.

    The half-life takes into account not only elimination from the body but also
    radioactive decay. If there is ever a question about residual activity in the body,
    the calculation uses the effective half-life; in radiation dosimetry calculations,

    the only half-life that is included in the equation is the effective half-life. 

    12.4.1 Physical half Lives

    Physical half-life is defined as the period of time required to reduce the
    radioactivity level of a source to exactly one half its original value due solely to

    radioactive decay. The physical half-life is designated Tp or more commonly 

    By default, the term T12 refers to the physical half-life and Tp
     is used when either or both of the other two half-lives are
    included in the discussion.
    Where λ is the radioactive constant of the radio substance

    There are a few things to note about the Tp :
    • The Tp can be measured directly by counting a sample at 2 different
    points in time and then calculating what the half-life is.

    • For example, if activity decreases from 100% to 25% in 24 hours, then
    the half-life is 12 hours since a decrease from 100% to 50% to 25%
    implies that 2 half-lives have elapsed.

    The physical half-life is unaffected by anything that humans can do to the
    isotope. High or low pressure or high or low temperature has no effect on the

    decay rate of a radioisotope.

     12.4.2 Biological half lives
    Biological Half-life is defined as the period of time required to reduce the
    amount of a drug in an organ or the body to exactly one half its original value
    due solely to biological elimination. It is typically designated Tb . There are a

    few things to note about the Tb

    For radioactive compounds, we have to calculate the Tb because
    the mass of the isotope is usually on the nanogram scale and, when
    distributed throughout the body, and especially in the target organ,
    concentrations are in the pictogram/ml range, much too small to
    measure directly.
    • For non-radioactive compounds, we can measure the Tb directly. For
    example, assuming that a person is not allergic to penicillin, we could
    give 1 000 mg of the drug and then measure the amount present in the
    blood pool and in the urine since we administered such a large amount
    of the drug

    Tb is affected by many external factors. Perhaps the two most important
    are hepatic and renal function. If kidneys are not working well, we

    would expect to see a high background activity on our scans. 

    • Each individual organ in the body has its own Tb and the whole body
    also has a Tb representing the weighted average of the Tb of all internal
    organs and the blood pool. It is therefore very important to have a frame
    of reference. For example, do you need to know the Tb of the drug in the

    liver or in the whole body? 

    • All drugs have aTb , not just radioactive ones. Drug package inserts
    often refer to the half-time of clearance of a drug from the blood pool
    or through the kidneys.
    • Since the whole body has a Tb representing the weighted average
    of the Tb of all internal organs, it will almost never equal that of an

    internal organ. 

    12.4.3 Effective half lives

    Effective half-life
    is defined as the period of time required to reduce the
    radioactivity level of an internal organ or of the whole body to exactly one half

    its original value due to both elimination and decay. 

    It is designated Te can be measured directly. For example, one can hold a 
    detection device 1 m from the patient’s chest and count the patient multiple

    times until the reading decreases to half of the initial reading. 

    The patient is permitted to use the rest room between readings as needed, so
    both elimination and decay are taking place. The half-life being measured in
    this case is the Te and Te is affected by the same external factors that affect Tb

    since Te is dependent upon Tb

    Where
    Tp: physical half-life

    Tb : biological half-life

    END UNIT ASSESSMENT 12

    A. Multiple choices.

    1. Which of the following would reduce the cell damage due to
    radiation for a lab technician who works with radioactive isotopes
    in a hospital or lab?
    a. Increase the worker’s distance from the radiation source.
    b. Decrease the time the worker is exposed to the radiation.
    c. Use shielding to reduce the amount of radiation that strikes
    the worker.
    d. Have the worker wear a radiation badge when working with
    the radioactive isotopes.
    e. All of the above.
    2. If the same dose of each type of radiation was provided over the
    same amount of time, which type would be most harmful?
    a. X-rays.                                       c. γ rays.
    b. α Rays.                                    d. β particles.

    3. Which of the following is true?

    a. Any amount of radiation is harmful to living tissue.
    b. Radiation is a natural part of the environment.
    c. All forms of radiation will penetrate deep into living tissue.
    d. None of the above is true.
    4. Which radiation induces the most biological damage for a given
    amount of energy deposited in tissue?
    a. Alpha particules.
    b. Gamma radiation.
    c. C. Beta radiation.
    d. D. All do the same damage for the same deposited energy.
    5. Which would produce the most energy in a single reaction?
    a. The fission reaction associated with uranium-235.
    b. The fusion reaction of the Sun (two hydrogen nuclei fused to
    one helium nucleus).
    c. Both (A) and (B) are about the same.
    d. Need more information.
    6. The fuel necessary for fusion-produced energy could be derived from

    a. Water.                       d. Superconductors.
    b. Uranium.                 e. Helium.
    c. Sunlight.

    B. Structured questions

    7. If the equipment isn’t working and my treatment is delayed or
    postponed, who checks that it is safe to use again? And will this delay
    affect my cancer?
    8. Do you have weekly chart rounds where you review patient-related
    information in peer review?
    9. Will you take imaging scans regularly during my treatment to verify
    position of my treatment? Who reviews those scans?
    10. People who work around metals that emit alpha particles are trained
    that there is little danger from proximity or touching the material, but
    they must take extreme precautions against ingesting it. Why? (Eating
    and drinking while working are forbidden.)
    11. What is the difference between absorbed dose and effective dose? What
    are the SI units for each?
    12. Radiation is sometimes used to sterilize medical supplies and even food.
    Explain how it works.
    13. How might radioactive tracers be used to find a leak in a pipe?
    14. Explain that there are situations in which we may or may not have
    control over our exposure to ionizing radiation.
    a. When do we not have control over our exposure to radiation?
    b. When do we have control over our exposure to radiation?
    c. Why might we want to limit our exposure to radiation when
    possible?
    15. Does exposure to heavy ions at the level that would occur during
     deep space missions of long duration pose a risk to the integrity and function

    of the central nervous system?
    16. Radiation protection of ionizing radiation from radiation sources is
    particularly difficult. Give a reason for this difficulty. 

    C. Essay questions

    17. I always lock my radioactive material-use rooms. However, renovators
    came in during the weekend, worked, and left the door open while they
    were on their lunch break. Am I responsible and how can I prevent this
    from happening? Debate on the situation above to support your answer.
    18. How can I ensure that personnel who work in my lab, but do not use
    radioactive material, do not violate the security requirements? Debate
    to support your idea.
    19. A Housekeeping staff member opens my radioactive material-use room
    after working hours and does not lock it when they leave. What should
    I do? Explain clearly to support your idea.
    20. Make a research and predict what steps that can or might be taken to
    reduce the exposure to radiation (consider if living near a radioactive
    area like an abandoned uranium mine, if finding a radioactive source, or

    in the event of a nuclear explosion or accident). 

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