# Chapter 3: Radiation Therapy Physics

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1. 1 mCi is equivalent to:
A. 3.7 x 1010 disintegrations/min
B. 3.7 x 104 disintegrations/sec
C. 3.7 x 10-2 disintegrations/sec
D. 2.22 x 1012 disintegrations/min
D. Conversion of dps to dpm means multiplying by 60 seconds. The converting mCi to Ci requires multiplying by 1000 or 103
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2. The half-life of iridium 192 is 74 days. The decay constant is:
a. 3.7 days-1
b. 37 days-1
c. 106.6 days-1
d. 0.0094 days-1
e. 0.027 days-1
d. Given by the formula λ=ln2/T1/2
3. What are the differences between the electron and proton?
• Electrons are light, negatively charged particles; they can collide and interact with other particles.
• Protons are heavy, positively charged particles; only interact with electrons
4. Types of nuclear decay include all of the following except:
A. Alpha decay
B. Neutron decay
C. Beta decay
D. Internal conversion
B. Types of nuclear decay include alpha, beta negative and positive, electron capture, internal conversion, fission and fusion aftermaths
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5. During x-ray production, the resulting x-ray beam comes from electrons colliding with the target causing interactions such as:
c. Auger electrons
d. All of the above
d. During ionization characteristic x-rays may be produced. If the electron comes close to the nucleus, bremsstrahlung radiation may result. Auger electrons may be emitted as a result of another electron filling an empty space left by the ejected electron.
6. The positive side of the basic x-ray tube is known as the:
A. Anode
B. Vacuum
C. Cathode
D. Filament
A. In the basic x-ray tube, the anode receives the streaming electrons and is known as the positive side of the tube.
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7. A radioactive source has an initial activity of 60 mCi. Its half-life is 8 days. What is the remaining activity after 10 days?
A. 30 mCi
B. 40 mCi
C. 25 mCi
D. 20 mCi
C. Use the activity formula A= Ao e-λt
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8. The average life of the source above is:
A. 11.5 days
B. 12.3 days
C. 0.086 days
D. 16 days
A. Use the formula Average life=1.44(T1/2)
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9. The ratio of x-ray to heat during x-ray production is:
A. Variable depending on the maximum energy of electrons traversing the tube
B. Variable depending on the strength of the target
C. Constant at 90% heat and 10% x-ray
D. Constant at 99% heat and 1% x-ray
A. As the maximum energy increases, more of the converted energy becomes photons
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A. Secular equilibrium
B. Decay constant
C. Fraction decay rate
D. Transient equilibrium
B. The decay constant expresses how many atoms are lost over time
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11. An elastic collision is one in which:
A. The incoming electron give all of its energy to the electron it encounters
B. The incoming electron shares its energy with the electron it encounters
C. The incoming electron takes the place of an ejected electron
D. The incoming electron is captured by the nucleus
A. In elastic collisions the incoming electrons gives up all of its energy. On the other hand, inelastic collisions may allow bounce back where the incoming electron shares its energy
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12. The energy of an electromagnetic radiation is inversely proportional to its:
A. Speed
B. Frequency
C. Mass
D. Wavelength
D. The electromagnetic spectrum shows wavelengths shortening as energy increases
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13. If a 50 keV electron collides with an inner shell electron with a binding energy of 25 keV, the resulting photoelectron will have an energy of:
A. 25 keV
B. 75 keV
C. 150 keV
D. 100 keV
A. The outgoing photoelectron has an energy that is the difference between the incoming electron and the binding energy of the electron collided
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14. The energy of an electromagnetic radiation is directly proportional to its:
A. a and b
B. Velocity
C. Frequency
D. Wavelength
C. The electromagnetic spectrum show that the frequency increases as the energy of radiation increases
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15. Photon Interactions include______.
Electron interactions include____.
• Photon Interactions: photodisintegrations, coherent scattering, photoelectric effect (Rayleigh), compton effect, pair production
• Electron Interactions: Bremsstrahlung, Characteristic
16. The decay of cobalt-60 to table lead is an example of ___ decay.
A. fusion
B. beta positive
C. beta negative
D. alpha
C. As radioactive Cobalt transforms, gamma rays and beta negative particles are emitted
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17. Regarding isotopes; isotopes of an element have the same number of ____ but a different numbers of neutrons.
Protons. Radionuclides with the same number of protons but different number of neutrons are known as isotopes
18. A photon of 25 Ä has a kinetic energy of ______ KeV.
• 0.496 KeV
• E= 12.4/λ
• E=12.4/25 A
• E=0.496 KeV
19. If the decay constant of a particular isotope is 45 sec-1, the half-life is ____.
• 0.0154 sec
• T1/2=.693/λ
• T1/2=.693/ 45 sec-1
• T1/2=.0154 sec
20. If the half-life of cobalt-60 is 5.26 years, the average life is _____
• 7.59 years
• Ta=T1/2/.693
• Ta=5.26/.693
• Ta=7.59 years
21. If using a tungsten target, the fraction of 4 MeV electrons converted to photons is ____.
• 0.1036 or 10.36%
• F=3.5x10-4 (74) (4 MeV)
• F=0.1036
22. Which has the highest photon energy?
B. Microwaves
C. Infrared
D. Ultraviolet light
D. The electronmagnetic spectrum shows UV light with higher energy and frequency than the other photons mentioned
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23. The probability of a photoelectric interaction (increases/decreases) with increasing energy and (increases/decreases) with the atomic number of the medium.
Decrease, Increase. The probability of photoelectric interactions decreases as energy increases. The probability of photoelectric interactions increases as the atomic number of the medium increases.
24. The majority of the mass of the atom is derived from:
A. Protons, neutrons, and electrons in the nucleus
B. Protons and neutrons in the nucleus
C. Protons and electrons in the nucleus
D. Alpha, beta, and gamma radiation emitted
B. Bohr's model shows the massive part of the atom being the nucleus where protons and neutrons reside
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25. A neutral atom that loses an electron by ionization is called a:
A. Positive ion
B. Negative atom
C. Positive atom
D. Negative ion
A. Loss of an electron leaves an imbalance to the atom. Positive charge would then be greater than negative charges
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26. After alpha decay, the daughter nuclide will have an atomic mass number ___ amu lower than the parent.
A. 2
B. 1
C. 6
D. 4
D. An alpha particle is composed of 2 neutrons and 2 protons. Loss of these particles would be a loss of 4 atomic mass units
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27. A certain atom has binding energies of 70 eV in the L shell and 10 eV in the M shell. During an M shell to L shell transition, the photon emitted will have an energy of:
A. 80 eV
B. 35 eV
C. 60 eV
D. 5 eV
C. The emitted photon has an energy that is the difference between the binding energies of transitioning electrons
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28. What type of nuclear decay is realized when:
a. 88Ra226 decays to 86Rn222 ____
b. 11Na22 decays to 10Ne22 ____
• a. Alpha decay
• b. Beta positive
29. An atom is neutral if the number of its electrons is equal to its:
A. Nucleons
B. Protons
C. Atomic weight
d. None of the above
B. Electrons have negative charge, protons positive charge. When equal, they neutralize the atom
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30. What is the threshold energy for pair production:
A. 0.511 MeV
B. 1.53 MeV
C. 1.02 MeV
D. 9.81 MeV
C. During pair production, two particles of equal energies -.511 MeV are emitted. The incoming photon has to have at least that photon has to have at least that combined energy
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31. Solve for λ in hours-1
A= 10 mCi
Ao= 18 mCi
t= 50 hours
• A=Aoe-λt
• 5 mCi= 18 mCi e-λ(50)
• 5/8=e-λ(50)
• ln 5/18=ln(e-λ(50))
• -1.28=-λ(50)
• λ=.0256-1hours
32. Solve for Ao
A= 10 mCi
T1/2= 8 hours
t=22 hours
• λ=.693/8hrs, λ=.087-1hours
• 10mCi=-Aoe-.087(22)
• Ao=67.57 mCi
33. The System International unit for activity is the:
A. Hertz
B. Becquerel
C. Roentgen
D. Curie
B. Activity is expressed in units of Curie or Becquerel. The Becquerel is the SI unit
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34. To interact by photoelectric effect, the interacting photon must have energy:
A. Less than the binding energy of the orbiting electron
B. Equal to or greater than the binding energy of the orbiting electron
C. Of any level
D. Of at least 1 MeV
B. Photoelectric effect occurs when a photon interacts with a tightly bound electron. Its energy has to be equal to or greater than the binding energy
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35. The photons produced during the orbital transitions of electrons from a higher to lower energy are called:
B. Characteristic radiation is emitting when electrons switch places in the shells of the atom
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36. An electron with the lowest binding energy is most likely located in the:
A. K shell
B. M shell
C. All binding energies are the same
D. L shell
B. The farther away from the nucleus, the lower the binding energy
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37. Two or more chemicals with the same chemical formula, but having different nuclear states are known as:
A. Isotopes
B. Isotones
C. Isomers
D. Isobars
C. Isomers are the same element but in an excited state
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38. Which is not true of the electromagnetic spectrum? They all have the same:
A. Velocity
B. Energy
C. Mass
D. Charge
B. Electromagnetic radiations have the potential to travel at the same speed, they have virtually no mass and carry no charge
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39. Radon has a half-life of 3.83 days. Its average life is:
A. 4.4 days
B. 3.83 days
C. 5.5 days
D. 6.6 days
C. Use the formula Average life = 1.44 (T1/2)
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40. Carbon-14 and nitrogen-14 are:
A. Isobars
B. Isomers
C. Isotopes
D. Isotones
A. Isobars have the same mass
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41. How many disintegrations per minute (dpm) are there in 1 Ci?
A.29.7 x 1018 dpm
B.2.2 x 1012 dpm
C.3.14 x 1021 dpm
D. 3.7 x 1010dpm
D. 1 Ci=3.7 x 1010 dps. Covert to minutes by multiplying by 60
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42. How many electrons are there in 1 g of tissue?
a. 3 x 1010
b. 3 x 1023
c. 6.02 x 1023
d. None of the above
d. The number of electrons per gram as been computed using Helium as a reference. For Helium 3x10^23 is the number of electrons per gram. Tissue in the question has not been specified as soft tissue or bone, both having a different atomic weight than helium
43. On January 1, we received 80 mCi of an isotope with a half-life of 8 days. The activity remaining on January 25 would be:
A. 10 mCi
B. 20 mCi
C. 8 mCi
D. 40 mCi
A. 24 days have elapsed. This would be 3 half-life periods for this isotope. 3 half lives would leave about 12.5% of the initial activity. 80 mCi (12.5%) = 10 mCi. The activity formula could also be used
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44. The fraction of cobalt-60 atoms remaining after 10 years is approximately:
A. 1/2
B. 1/4
C. 1/8
D. 1/3
B. The half-life of Cobalt is 5.26 years. 10 years is approximately 2 half lives, leaving about 25% of the original atoms
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45. The wavelengths of x-rays are measured in:
A. centimeters
B. Angstroms
C. Roentgens
D. millimeters
B. The Angstrom is the unit of measure for the wavelength
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46. The relationship between mass and energy is given by Einstein's equation: E=mc2
The C stands for:
A. Energy
B. 3 x 108 cm/second
C. Mass
D. Velocity of light
D. C in Einstein's equation is the speed or velocity of light. Option D has incorrect time units
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47. The photoelectric process is essentially an interaction between a photon and:
A. The nucleus
B. A bound electron
C. A free electron
d. All of the above
B. Photoelectric effect often occurs with an electron tightly bound and in the inner shells of the atom
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48. As the wavelength of light is decreased, its speed is:
A. Increased exponentially
B. Decreased linearly
C. Increased linearly
D. Unchanged
D. All radiations in the electromagnetic spectrum have the same speed/velocity regardless of wavelength or frequency
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49. The frequency of radiation with a wavelength of 5 x 10^-7 meters is:
A. 6 x 10^-15 Hz
B. 6 x 10^14 Hz
C. 3 x 10^8 Hz
D. 1.66 x 10^-15 Hz
E. 1.66 x 10^15 Hz
B. use the formula C=λν
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50. A radionuclide decays at the rate of 20% per hour. Its half-life is approximately:
A. 2 hrs
B. 3.5 hrs
C. 4 hrs
D. 2.5 hrs
E. 3 hrs
B. use the formula T1/2=.693/λ
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51. Bragg peak is:
A. The maximum activity of an isotope
B. An ionization maximum near the end of the range of a heavy charged particle
C. A maximum concentration of Compton interactions
D. A maximum in the curve of activity and time for a parent and daughter radionuclide in equilibrium
D. Bragg peak shows maximum ionization at the end of the range for heavy, high LET particles
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52. Different isotopes of the same element will have equal numbers of ______
A. Electrons and neutrons
B. Protons and neutrons
C. Neutrons
D. Protons and electrons
E. Electrons
D. Isotopes have the same number of protons and different neutrons. The number of protons and electrons are equal in a neutral atom
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53. A radioactive source has a half-life of 6 hours and an activity of 10 mCi at noon on Monday. The activity at noon on Tuesday will be ____mCi.
A. 0.31
B.2.5
C. 6.25
D.0.625
E. 9.375
A. The time elapsed has been 4 half-lives. The activity may be found by multiplying the initial activity by 0.5^4. Or the formula A=Aoe^(-λt) may also be used
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54. The half-life of a radionuclide is:
A. Less than the average life
B. Usually shorter for beta negative than beta positive emitters
C. Influenced by temperature and pressure
D. Directly proportional to the decay constant
A. The average life is given by the formula: Ta=1.44 (T1/2). So, the half-life is less than the average life. The average life comes close to what may be thought of as the life span for a radioactive nuclide
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55. In the formula A=Aoe-λt, λ is ____.
A. The number of atoms decaying per unit of time
B. The linear attenuation coefficient
C. The fraction of atoms decaying in time
D. The fraction of atoms decaying per unit of time
D. The symbol in the activity formula is the decay constant and expressed the constant fraction of atoms decaying in a certain amount of time
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56. When a very long-lived radionuclide decays to a short-lived daughter, it is known as ___equilibrium.
A. transient
B. secular
C. thermal
D. temporary
B. Secular equilibrium occurs when the parent nuclide has a longer half-life than a daughter product
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57. Which of the following is not a type of ionizing radiation?
A. 2 MHz ultrasound
B. Strontium beta
C. 15 MV x-rays
D. Cobalt gamma rays
A. Ultrasound is not electromagnetic radiation
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58. An electron, proton, and alpha particle each have 20 MeV kinetic energy. Which of the following is true?
A. The proton has the highest total energy
B. The electron travels at almost light speed
C. The alpha particle travels at almost light speed
D. The alpha particle has the least total energy
B. The electron's mass is low compared to its kinetic energy so it must be traveling at about light speed. The alpha particle has the greatest total energy
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59. The mass of an electron is:
A. Half that of a proton
B. The same as a proton
C. The same as a neutron
D. Much smaller than that of a neutron
D. protons, neutrons and nucleons have a mass about 1800 times that of an electron
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60. Ionization implies:
A. The removal of an electron from the atom
B. An excited state of the stom
C. The production of x-rays
D. A neutral state of the atom
A. When an atom is ionized, an electron is ejected from the atom
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61. A deuteron is the nucleus of an isotope of H2. Which of the following is true?
A. It has a atomic number of 2
B. It has a mass number of 2
C. It has a positive charge of 2
D. It has a energy of 2 MeV
B. The number in the upper right indicates the atomic mass
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A. The nucleus
B. Inner shell electrons
C. Outer shell electrons
d. All of the above
A. Unstable radioactive nuclides has excess energy in its nucleus. The nucleus achieves stability by redistributing energy between the nucleons
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63. The probability that a photon interacts with a material is:
A. Inversely proportional to the number of protons in the atom
B. Dependent on its density
C. Proportional to the total attenuation coefficient
d. All of the above
C. The total attenuation coefficient represents the sum of all possible interactions
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64. The rate of energy loss by a charged particle is:
A. Proportional to the particle charge
B. Independent of charge
C. Proportional to the square of the particle charge
d. None of the above
C. Energy loss is proportional to the square of particle charge and inversely proportional to the square of its velocity
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65. Heavy particles lose most of their energy
A. Near the end of their range
B. In the middle of their range
C. Immediately as they enter the medium
D. Equally throughout their range
A. This maximum energy loss is known as Bragg peak
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66. Bragg peak is not observed in electrons because of their:
A. Short half-life
B. High speed
C. Negative charge
D. Small mass
D. Electrons have low mass and therefore deposit energy as it moves quickly through the medium
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67. Excitation produced by electron beams occurs in the:
A. Nucleus of the atom
B. Orbital electrons of the atom
C. Neutrons of the atom
D. Protons of the atom
B. The energy transferred is not enough to eject the electron. The incoming electron does not have an energy higher than the binding energy of the orbiting electron
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68. In the production of bremsstrahlung, the electron:
A. Ejects an electron from the atom
B. Produces a heavy particle
C. Slows down and loses some of its energy as an x-ray photon
D. Ejects a cloud of electrons
C. The strong electromagnetic field of the nucleus decelerates the electron as it approaches. In the deceleration, some of the energy is lost in the form of an x-ray photon called bremsstrahlung
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69. The term xray refers to a part of the electromagnetic spectrum having an energy of:
A. Between 100 and 1 million electron volts
B. More than 1 million electron volts
C. Less than 1 electron volt
D. Between 1 and 100 electron volts
A. The electromagnetic spectrum shows xrays having energy of at least 124 eV
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70. Which of the following types of radiation has a positive electrical charge?
A. Alpha
B. Gamma
C. Beta
D. Delta
A. Alpha particles have a positive charge
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71. Radiation can be described as energy:
A. Destroyed
B. in the form of heat
C. In transit
D. Recovered
C. Radiation is energy in motion
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72. I131 and I125 have different:
A. Chemical properties
B. K shell binding energies
C. Numbers of protons
D. Numbers of neutrons
E. Z values
D. The formulas show the element Iodine which has the same chemical properties. The mass number is different, and the z number is the same at 53 protons so the number of neutrons are different
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73. If the distant from a radiation source is decreased by half, the intensity is:
A. Increased by half
B. Decrease by half
C. Increased by four times
D. Decreased by a quarter
C. Inverse square law says the intensity of radiation is inversely proportional to the distance by a square of distance change
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74. 106 photons from a source are incident on a 1.5 cm thick lead plate. The HVL of the beam in lead is 1.1 cm. The number of photons transmitted through the lead plate would be:
• N=Noe^(-μt)
• N=389,000
75. 108 photons from a source are incident on a water tank 0.2 meters thick. The linear attenuation coefficient of this beam in water is 11.55 m-1. The number of photons transmitted through this 0.2 meters of water would be:
• N=108e(-11.55(0.2))
• N=9,900,000

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 Author: TranDo92 ID: 287276 Filename: Chapter 3: Radiation Therapy Physics Updated: 2014-11-08 04:55:25 Tags: Physics Folders: Description: Review Book: Chapter 3 Show Answers:

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