DABMP
DABMP - AMERICAN BOARD OF MEDICAL PHYSICS
DIPLOMATE | EXAM QUESTIONS AND CORRECT
ANSWERS | 2026/2027
AMERICAN BOARD OF MEDICAL PHYSICS - DIPLOMATE (DABMP)
1. In soft tissue, which interaction dominates for photon energies
between roughly 1 and 10 MeV?
A. Compton scattering
B. Coherent (Rayleigh) scattering
C. Pair production
D. Photoelectric absorption
A. Compton scattering
Compton scattering dominates in water-like media across most of the
megavoltage therapy range because it depends on electron density rather
than atomic number.
Page 1 of 88
, DABMP
2. The probability of photoelectric absorption per gram varies
approximately as:
A. Z³/E³
B. E/Z³
C. Z/E
D. Z²/E
A. Z³/E³
Photoelectric interaction rises steeply with atomic number and falls
steeply with photon energy, roughly as Z³/E³, which is the basis of
contrast in diagnostic imaging.
3. What is the threshold photon energy for pair production in the field
of a nucleus?
A. 1.33 MeV
B. 0.511 MeV
C. 2.044 MeV
D. 1.022 MeV
D. 1.022 MeV
Pair production requires enough energy to create the rest mass of an
electron and a positron, 2 × 0.511 MeV.
4. Triplet production, occurring in the field of an orbital electron, has a
threshold of:
A. 0.511 MeV
B. 3.066 MeV
C. 2.044 MeV
D. 1.022 MeV
C. 2.044 MeV
Momentum conservation with a light recoiling electron raises the
threshold to four electron rest masses, 2.044 MeV.
Page 2 of 88
, DABMP
5. The Compton mass attenuation coefficient is nearly independent of
atomic number because it depends mainly on:
A. Binding energy of K-shell electrons
B. Density of the absorber in g/cm³
C. Electrons per gram of the absorber
D. Nuclear charge of the absorber
C. Electrons per gram of the absorber
Electrons per gram is nearly constant for most elements (except
hydrogen), so Compton attenuation per gram changes little with Z.
6. Maximum energy is transferred to the Compton recoil electron when
the photon is scattered at:
A. 45°
B. 180°
C. 90°
D. 0°
B. 180°
A head-on collision with photon backscatter gives the electron the largest
possible kinetic energy, which defines the Compton edge.
7. For a very high-energy incident photon, the energy of a photon
backscattered at 180° approaches:
A. 0.255 MeV
B. 0.511 MeV
C. 1.022 MeV
D. 0.0 MeV
A. 0.255 MeV
As incident energy becomes large, the 180° scattered photon energy
approaches m₀c²/2, about 0.255 MeV.
Page 3 of 88
, DABMP
8. The half-value layer of a narrow monoenergetic beam is related to
the linear attenuation coefficient by:
A. HVL = 0.693/μ
B. HVL = 2.303/μ
C. HVL = μ/0.693
D. HVL = 1/μ
A. HVL = 0.693/μ
Setting the transmitted fraction e^(−μx) equal to one-half gives x = ln2/μ.
9. The mass attenuation coefficient is commonly expressed in units of:
A. g/cm³
B. g/cm²
C. cm²/g
D. cm⁻¹
C. cm²/g
Dividing the linear coefficient (cm⁻¹) by density (g/cm³) yields cm²/g,
which removes the dependence on physical density.
10. A characteristic x-ray emitted when an L-shell electron fills a K-
shell vacancy is designated:
A. Mα
B. Kα
C. Lα
D. Kβ
B. Kα
Kα refers to L-to-K transitions; Kβ refers to transitions from the M shell
or higher into the K shell.
11. Auger electron emission is favored over characteristic x-ray
emission in:
A. Low atomic number elements
B. Elements heavier than lead only
C. Positron-emitting nuclides only
D. High atomic number elements
A. Low atomic number elements
Fluorescence yield increases with Z, so in light elements the vacancy
energy is more often carried away by an Auger electron.
Page 4 of 88
DABMP - AMERICAN BOARD OF MEDICAL PHYSICS
DIPLOMATE | EXAM QUESTIONS AND CORRECT
ANSWERS | 2026/2027
AMERICAN BOARD OF MEDICAL PHYSICS - DIPLOMATE (DABMP)
1. In soft tissue, which interaction dominates for photon energies
between roughly 1 and 10 MeV?
A. Compton scattering
B. Coherent (Rayleigh) scattering
C. Pair production
D. Photoelectric absorption
A. Compton scattering
Compton scattering dominates in water-like media across most of the
megavoltage therapy range because it depends on electron density rather
than atomic number.
Page 1 of 88
, DABMP
2. The probability of photoelectric absorption per gram varies
approximately as:
A. Z³/E³
B. E/Z³
C. Z/E
D. Z²/E
A. Z³/E³
Photoelectric interaction rises steeply with atomic number and falls
steeply with photon energy, roughly as Z³/E³, which is the basis of
contrast in diagnostic imaging.
3. What is the threshold photon energy for pair production in the field
of a nucleus?
A. 1.33 MeV
B. 0.511 MeV
C. 2.044 MeV
D. 1.022 MeV
D. 1.022 MeV
Pair production requires enough energy to create the rest mass of an
electron and a positron, 2 × 0.511 MeV.
4. Triplet production, occurring in the field of an orbital electron, has a
threshold of:
A. 0.511 MeV
B. 3.066 MeV
C. 2.044 MeV
D. 1.022 MeV
C. 2.044 MeV
Momentum conservation with a light recoiling electron raises the
threshold to four electron rest masses, 2.044 MeV.
Page 2 of 88
, DABMP
5. The Compton mass attenuation coefficient is nearly independent of
atomic number because it depends mainly on:
A. Binding energy of K-shell electrons
B. Density of the absorber in g/cm³
C. Electrons per gram of the absorber
D. Nuclear charge of the absorber
C. Electrons per gram of the absorber
Electrons per gram is nearly constant for most elements (except
hydrogen), so Compton attenuation per gram changes little with Z.
6. Maximum energy is transferred to the Compton recoil electron when
the photon is scattered at:
A. 45°
B. 180°
C. 90°
D. 0°
B. 180°
A head-on collision with photon backscatter gives the electron the largest
possible kinetic energy, which defines the Compton edge.
7. For a very high-energy incident photon, the energy of a photon
backscattered at 180° approaches:
A. 0.255 MeV
B. 0.511 MeV
C. 1.022 MeV
D. 0.0 MeV
A. 0.255 MeV
As incident energy becomes large, the 180° scattered photon energy
approaches m₀c²/2, about 0.255 MeV.
Page 3 of 88
, DABMP
8. The half-value layer of a narrow monoenergetic beam is related to
the linear attenuation coefficient by:
A. HVL = 0.693/μ
B. HVL = 2.303/μ
C. HVL = μ/0.693
D. HVL = 1/μ
A. HVL = 0.693/μ
Setting the transmitted fraction e^(−μx) equal to one-half gives x = ln2/μ.
9. The mass attenuation coefficient is commonly expressed in units of:
A. g/cm³
B. g/cm²
C. cm²/g
D. cm⁻¹
C. cm²/g
Dividing the linear coefficient (cm⁻¹) by density (g/cm³) yields cm²/g,
which removes the dependence on physical density.
10. A characteristic x-ray emitted when an L-shell electron fills a K-
shell vacancy is designated:
A. Mα
B. Kα
C. Lα
D. Kβ
B. Kα
Kα refers to L-to-K transitions; Kβ refers to transitions from the M shell
or higher into the K shell.
11. Auger electron emission is favored over characteristic x-ray
emission in:
A. Low atomic number elements
B. Elements heavier than lead only
C. Positron-emitting nuclides only
D. High atomic number elements
A. Low atomic number elements
Fluorescence yield increases with Z, so in light elements the vacancy
energy is more often carried away by an Auger electron.
Page 4 of 88
