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RSO Exam PHYSICIST INDIA > Ionizing Radiation Interaction > Flashcards

Ionizing Radiation Interaction Flashcards

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1
Q
A
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2
Q

What happens when an x-ray or γ-ray beam passes through a medium?

A

Interaction between photons and matter takes place, resulting in energy transfer to the medium

This interaction may lead to ionization and excitation of atoms.

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3
Q

What is the initial step in the energy transfer process when ionizing radiation interacts with a medium?

A

The ejection of electrons from the atoms of the absorbing medium

This process is crucial for the transfer of energy.

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4
Q

What is ionization?

A

The process by which a neutral atom acquires a positive or a negative charge

Ionization can occur when ionizing radiations strip electrons from atoms.

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5
Q

Define a positive ion.

A

An atom from which an electron has been removed

Positive ions are a result of the ionization process.

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6
Q

What is an ion pair?

A

The combination of a positively charged ion and a negatively charged ion (usually a free electron)

Ion pairs are formed during the ionization process.

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7
Q

What are directly ionizing radiations?

A

Charged particles such as electrons, protons, and α-particles with sufficient kinetic energy to produce ionization by collision

These particles can interact with matter to cause ionization.

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8
Q

How do charged particles lose energy while penetrating matter?

A

The energy is lost in a large number of small increments along the ionization track in the medium

This process can include interactions where ejected electrons produce secondary tracks.

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9
Q

What is a δ-ray?

A

An ejected electron that receives sufficient energy to produce a secondary track of its own

δ-rays are a result of interactions with high-speed electrons.

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10
Q

What happens to most of the absorbed energy in body tissues?

A

Most of the absorbed energy is converted into heat, producing no biologic effect

This means that not all energy transfer leads to harmful effects in biological tissues.

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11
Q

Fill in the blank: An atom acquires a _______ when it loses an electron.

A

positive charge

This defines the formation of a positive ion.

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12
Q

True or False: Ionizing radiation can lead to the destruction of reproductive capacity in cells.

A

True

Sufficient energy deposition within cells can have detrimental effects.

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13
Q

What is the process called when energy from an incident particle raises electrons to higher-energy levels without ejecting them?

A

Excitation

The process of excitation occurs when the energy lost by the incident particle is insufficient to eject an electron from the atom.

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14
Q

What type of radiation are uncharged particles such as neutrons and photons categorized as?

A

Indirectly ionizing radiation

Indirectly ionizing radiation liberates directly ionizing particles from matter when they interact with it.

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15
Q

What are the three major processes through which ionizing photons produce high-speed electrons?

A
  • Photoelectric effect
  • Compton effect
  • Pair production

These processes describe how ionizing photons interact with the atoms of a material.

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16
Q

What is the fluence (Φ) of photons defined as?

A

The quotient dN by da

dN is the number of photons that enter an imaginary sphere of cross-sectional area da.

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17
Q

Define fluence rate or flux density (φ).

A

Fluence per unit time

Fluence rate is calculated as Φ divided by dt, where dt is the time interval.

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18
Q

What is energy fluence (ψ) defined as?

A

The quotient of dEfl by da

dEfl is the sum of the energies of all the photons that enter a sphere of cross-sectional area da.

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19
Q

What is dEfl for a monoenergetic beam?

A

dEfl is the number of photons dN times energy hν carried by each photon.

This equation represents the energy contribution of individual photons in the beam.

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20
Q

Define energy fluence rate, energy flux density, or intensity (ψ).

A

Intensity (ψ) is the energy fluence per unit time.

This metric quantifies how much energy passes through a unit area over a specified time.

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21
Q

What is the purpose of the experimental arrangement shown in Figure 5.1?

A

To measure the attenuation characteristics of a photon beam.

The setup involves a narrow beam of monoenergetic photons and a variable thickness absorber.

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22
Q

Where is the detector placed in the experimental arrangement?

A

The detector is placed at a fixed distance from the source and sufficiently farther away from the absorber.

This ensures that only primary photons are measured.

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23
Q

What type of photons are measured by the detector in the arrangement?

A

Only the primary photons that passed through the absorber without interacting.

Scattered photons are not counted in this measurement.

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24
Q

What happens to a photon when it interacts with an atom in the context of this experiment?

A

It is either completely absorbed or scattered away from the detector.

This interaction affects the measurement of the photon beam’s intensity.

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25
What is the relationship between the reduction in the number of photons (dN) and the number of incident photons (N)?
dN is proportional to N and to the thickness of the absorber (dx) ## Footnote This relationship is mathematically expressed with the attenuation coefficient μ.
26
What does the attenuation coefficient (μ) represent?
The constant of proportionality in the reduction of photons as thickness increases ## Footnote It indicates the rate at which photons are absorbed by the material.
27
What are the units of the linear attenuation coefficient (μ) when thickness is measured in centimeters?
1/cm or cm−1
28
How is the attenuation equation expressed in terms of intensity (I)?
I(x) = I0 * e^(-μx) ## Footnote This equation shows how transmitted intensity decreases with thickness.
29
What is the half-value layer (HVL)?
The thickness of an absorber required to attenuate the intensity of the beam to half its original value ## Footnote Defined as the thickness at which I/I0 = 1/2.
30
What happens to the average energy of a transmitted beam as the thickness of the absorber increases?
The average energy increases or the beam becomes increasingly harder
31
What is the mass attenuation coefficient (μ/ρ)?
A coefficient that is independent of density and depends on the atomic composition of the material ## Footnote It is calculated by dividing the linear attenuation coefficient by the density.
32
What are the units of the mass attenuation coefficient?
cm²/g
33
What is the energy transfer coefficient (μtr)?
The fraction of photon energy transferred into kinetic energy of charged particles per unit thickness ## Footnote It is related to the linear attenuation coefficient.
34
What does the energy absorption coefficient (μen) represent?
The portion of energy absorbed by the material, accounting for energy lost to bremsstrahlung ## Footnote Defined as μtr * (1 - g), where g is the fraction of energy lost.
35
What are the five major types of interactions causing attenuation of a photon beam?
* Coherent scattering * Photoelectric effect * Compton effect * Pair production * Photodisintegration ## Footnote Photodisintegration is significant only at very high photon energies (>10 MeV).
36
What is coherent scattering?
An interaction where an electromagnetic wave passes near an electron, causing it to oscillate and reradiate energy at the same frequency ## Footnote It results in no energy loss and is most probable in high-atomic-number materials with low-energy photons.
37
What is the photoelectric effect?
A phenomenon where a photon is absorbed by an atom, ejecting one of its orbital electrons.
38
What is the equation for the kinetic energy of the ejected electron in the photoelectric effect?
KE = hν − EB, where EB is the binding energy of the electron.
39
What happens to the atom after an electron is ejected due to the photoelectric effect?
The atom is left in an excited state with a vacancy in the shell.
40
What can fill the vacancy created by the ejected electron in the photoelectric effect?
An outer shell electron can fill the vacancy, emitting a characteristic x-ray.
41
What are Auger electrons?
Electrons emitted when the energy released from filling a vacancy is given to another electron in a higher shell.
42
What is the binding energy of the K shell in soft tissues?
Approximately 0.5 keV.
43
How does the energy of characteristic photons differ in high-atomic-number materials compared to soft tissues?
Higher energy photons may deposit energy at larger distances compared to the range of the photoelectron.
44
What is the relationship between the mass photoelectric attenuation coefficient (τ/ρ) and photon energy?
The graph on logarithmic paper is almost a straight line with a slope of approximately -3.
45
What are absorption edges?
Discontinuities in the graph of photoelectric attenuation, corresponding to the binding energies of electron shells.
46
At what photon energy does resonance occur for L shell electrons?
At photon energies that equal the binding energy of the L shell.
47
What is the approximate relationship of photoelectric attenuation based on atomic number?
Photoelectric attenuation depends strongly on the atomic number of the absorbing material.
48
What is the angular distribution of emitted electrons in the photoelectric effect?
For low-energy photons, photoelectrons are emitted most likely at 90 degrees relative to the incident photon.
49
What occurs in the Compton effect?
A photon interacts with an atomic electron, causing the electron to be emitted and the photon to be scattered.
50
What happens during a direct hit in the Compton effect?
The electron travels forward (θ = 0 degrees) and the scattered photon travels backward (φ = 180 degrees).
51
What occurs during a grazing hit in the Compton effect?
The electron is emitted at right angles (θ = 90 degrees) and the scattered photon moves forward (φ = 0 degrees).
52
What is the result of a 90-degree photon scatter in the Compton effect?
The angle of electron emission depends on α, calculated from conservation equations.
53
How does the Compton effect behave with low-energy photons?
The scattered photon has approximately the same energy as the original photon.
54
What happens when high-energy photons interact in the Compton effect?
The scattered photon has much less energy, causing significant energy absorption.
55
Why is the energy of photons scattered at 90 degrees important?
It is crucial for calculating barrier or wall thickness against scattered radiation.
56
What is the maximum energy of radiation scattered at right angles for high-energy photons?
0.511 MeV ## Footnote This is independent of incident energy.
57
What is the maximum energy of radiation scattered backward for high-energy photons?
0.255 MeV ## Footnote This is also independent of incident energy.
58
What happens to the energy of photons scattered at angles less than 90 degrees?
Greater than 0.511 MeV and approaches the incident photon energy for forward scatter.
59
What is the threshold energy required for pair production?
1.02 MeV ## Footnote This energy is needed to create a pair of electrons.
60
What occurs during the pair production process?
A photon interacts with an atomic nucleus to create a negative electron and a positive electron.
61
What is the energy distribution of the electron-positron pair in pair production?
Each particle tends to acquire half the available kinetic energy.
62
What is annihilation radiation?
Two photons, each with 0.51 MeV energy, produced when a positron combines with an electron.
63
How does the probability of pair production change with atomic number?
Increases rapidly with atomic number (Z).
64
What relationship does the attenuation coefficient for pair production have with atomic number?
Varies with Z² per atom, Z per electron, and approximately Z per gram.
65
What is the total mass attenuation coefficient (μ/ρ)?
The sum of the four individual coefficients.
66
What type of interaction is coherent scattering important for?
Very low photon energies (<10 keV) and high-Z materials.
67
What happens to the mass attenuation coefficient as photon energy increases?
Decreases rapidly with energy.
68
What type of interaction predominates at photon energies much greater than 1.02 MeV?
Pair production.
69
What is the effect of atomic number on the Compton effect?
It is independent of atomic number Z.
70
How does the number of electrons per gram change with atomic number?
Decreases slowly but systematically with atomic number.
71
What can be said about the attenuation of a 60Co γ-ray beam in different materials of equal density?
Approximately the same attenuation will occur.
72
How much more will 1 cm of bone attenuate compared to 1 cm of soft tissue?
More, due to higher electron density.
73
What is the relationship between the Compton mass attenuation coefficient (σc/ρ) and the number of electrons per gram?
σc/ρ depends only on the number of electrons per gram.
74
Fill in the blank: The maximum energy of radiation scattered at angles between 90 and 180 degrees will lie between _______.
0.255 MeV and 0.511 MeV.
75
True or False: The Compton effect becomes more important as photon energy increases beyond the binding energy of the K electron.
True.
76
What must the energy of the incident photon be compared to for the Compton effect to occur?
Large compared with the electron-binding energy.
77
What is the most probable distribution of energy in the pair production process?
Each particle acquires half the available kinetic energy ## Footnote However, any energy distribution is possible, including one particle receiving all energy while the other receives none.
78
What is pair production?
An event in which energy is converted into mass, as predicted by Einstein’s equation E= mc2
79
What happens during the annihilation radiation process?
A positron combines with an electron to produce two photons, each having 0.51 MeV energy
80
How is the attenuation coefficient for pair production affected by atomic number?
Increases rapidly with atomic number ## Footnote The attenuation coefficient varies with Z² per atom, Z per electron, and approximately Z per gram.
81
What is the relationship between incident photon energy and the likelihood of pair production?
Increases as the logarithm of the incident photon energy above the threshold energy
82
What is the total mass attenuation coefficient?
The sum of the four individual coefficients
83
At what photon energy is coherent scattering important?
Very low photon energies (<10 keV) and high-Z materials
84
What is the dominant mode of interaction for photons in the Compton range of energies?
Compton effect
85
What is the threshold energy for pair production?
1.02 MeV
86
How do charged particles primarily interact with matter?
By ionization and excitation
87
What is stopping power (S)?
The rate of kinetic energy loss per unit path length of the particle
88
What is the Bragg peak?
The peaking of dose near the end of the particle range
89
What happens to the Bragg peak for electrons?
It is not observed due to multiple scattering
90
What is a secondary electron or Δ-ray?
An ejected electron that receives sufficient energy to produce an ionization track of its own
91
How do neutrons interact with matter?
By recoiling protons from hydrogen and recoiling heavy nuclei from other elements, and by nuclear disintegrations
92
What materials are most efficient for absorbing neutron beams?
Hydrogenous materials such as paraffin wax or polyethylene
93
What is the relationship between photon energy and the attenuation coefficient?
The attenuation coefficient decreases rapidly with energy
94
What is the primary interaction for charged particles?
Ionization and excitation
95
What is the formula relating the attenuation and half-value layer (HVL)?
HVL = 0.693/μ
96
What does the attenuation coefficient μ characterize?
Photon beam attenuation
97
What are the five major processes through which photon beams interact with matter?
* Coherent scattering * Photoelectric effect * Compton effect * Pair production * Photodisintegration
98
What is the probability of the photoelectric effect in water for photon energies up to 25 keV?
Predominant
99
How does Compton interaction probability in water change with photon energy?
Increases from 10 to 150 keV, then decreases with further energy increase
100
What is the maximum energy of a photon scattered at 90 degrees?
0.511 MeV
101
What type of radiation is produced by nuclear disintegrations from neutron interactions?
Heavy charged particles, neutrons, and γ-rays
102
What is the main contributor to the dose deposited in tissue from a high-energy neutron beam?
Recoil protons
103
What is the comparative depth dose distribution of neutron beams similar to?
Cobalt-60 γ-ray beams
104
What is a unique characteristic of proton beams in radiation therapy?
Ability to concentrate dose inside the target volume and minimize dose to surrounding normal tissues
105
What happens to Compton interaction probability in water as photon energy increases from 10 to 150 keV?
It increases with photon energy from 10 to 150 keV, then decreases with further increase in energy. ## Footnote Compton interaction is predominant in water for photon energies between 30 keV to 24 MeV.
106
What is the predominant mode of interaction in water for radiation therapy x-ray beams?
Compton interaction. ## Footnote This includes all x-ray beams used in radiation therapy.
107
Is Compton probability dependent on atomic number (Z)?
No, it is almost independent of Z. ## Footnote It depends on electron density (number of electrons per cubic centimeter).
108
What is the maximum energy of a photon scattered at 90 degrees?
0.511 MeV.
109
What is the threshold energy for pair production?
1.02 MeV. ## Footnote This energy is just enough to create an electron-positron pair.
110
How does pair production probability change with energy beyond 1.02 MeV?
It increases slowly with energy. ## Footnote For example, it increases from about 6% at 4 MeV to 20% at 7 MeV.
111
What does the pair production coefficient vary with?
It varies approximately as: * Z² per atom * Z per electron * Z per gram.
112
What is the reverse process of pair production?
Electron-positron annihilation. ## Footnote This process gives rise to two photons each of 0.511 MeV ejected in opposite directions.
113
What does photodisintegration involve?
A photon creating a nuclear reaction, often resulting in neutron emission. ## Footnote It is significant at high photon energies and can cause neutron contamination of therapy beams greater than 10 MV.
114
How do charged particles primarily interact?
By ionization and excitation. ## Footnote Radiative collisions (bremsstrahlung) are more likely for electrons than for heavier charged particles.
115
What characterizes the Bragg peak in charged particles?
All charged particles exhibit a Bragg peak near the end of their range.
116
Why is the Bragg peak not observed in electron beams?
Due to excessive scattering and smearing of the Bragg peaks.
117
How do neutrons interact?
By ejecting recoil protons or producing nuclear disintegrations.
118
What is an efficient absorber of x-rays?
Lead.
119
What is the most efficient absorber of neutrons?
Hydrogenous materials such as water, paraffin wax, and polyethylene.

RSO Exam PHYSICIST INDIA (5 decks)

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