ABR Medical Physics Certification
Examination – Full-Length Practice
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. Which quantity describes the amount of energy deposited per unit
mass of tissue by ionizing radiation?
A. Exposure
B. Kerma
C. Absorbed dose
D. Equivalent dose
Answer: C. Absorbed dose
Rationale: Absorbed dose (Gy) is defined as the energy imparted per unit
mass of matter by ionizing radiation.
2. The half-value layer (HVL) of an x-ray beam is defined as the thickness
of material that:
, A. Stops all photons
B. Reduces beam intensity by half
C. Doubles beam energy
D. Eliminates scatter radiation
Answer: B. Reduces beam intensity by half
Rationale: HVL measures beam quality and is the thickness of absorber
needed to reduce intensity to 50%.
3. Which interaction predominates for diagnostic x-rays in soft tissue
around 50 keV?
A. Photoelectric effect
B. Compton scattering
C. Pair production
D. Coherent scattering
Answer: B. Compton scattering
Rationale: In the diagnostic energy range, Compton interactions dominate
in soft tissue and are responsible for most scatter.
4. The SI unit of exposure is:
A. Gray
B. Sievert
C. Coulomb/kg
D. Roentgen
,Answer: C. Coulomb/kg
Rationale: Exposure is defined in terms of charge per mass of air, with the
SI unit being C/kg.
5. Which factor most strongly influences photoelectric absorption
probability?
A. Photon energy and atomic number
B. Density alone
C. Electron binding energy only
D. Tissue thickness
Answer: A. Photon energy and atomic number
Rationale: Photoelectric effect probability is proportional to Z³ and
inversely related to photon energy cubed.
6. In radiation protection, ALARA stands for:
A. As Low As Reasonably Achievable
B. As Little As Radiation Allowed
C. All Levels Are Regulated Always
D. Allowed Limits Are Reduced Annually
Answer: A. As Low As Reasonably Achievable
Rationale: ALARA is a guiding principle to minimize radiation exposure
while achieving clinical objectives.
7. Which dosimeter is most commonly used for personal monitoring of
occupational exposure?
, A. Ionization chamber
B. Thermoluminescent dosimeter
C. Geiger-Müller counter
D. Film badge
Answer: B. Thermoluminescent dosimeter
Rationale: TLDs are widely used for personnel monitoring due to accuracy,
reusability, and tissue-equivalent response.
8. The effective dose accounts for:
A. Only absorbed dose
B. Radiation weighting factors only
C. Tissue weighting and radiation weighting factors
D. Exposure time only
Answer: C. Tissue weighting and radiation weighting factors
Rationale: Effective dose (Sv) incorporates both radiation type and tissue
sensitivity.
9. What is the primary purpose of a flattening filter in a linear
accelerator?
A. Increase beam energy
B. Make the beam intensity uniform
C. Reduce electron contamination
D. Improve patient positioning
Examination – Full-Length Practice
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. Which quantity describes the amount of energy deposited per unit
mass of tissue by ionizing radiation?
A. Exposure
B. Kerma
C. Absorbed dose
D. Equivalent dose
Answer: C. Absorbed dose
Rationale: Absorbed dose (Gy) is defined as the energy imparted per unit
mass of matter by ionizing radiation.
2. The half-value layer (HVL) of an x-ray beam is defined as the thickness
of material that:
, A. Stops all photons
B. Reduces beam intensity by half
C. Doubles beam energy
D. Eliminates scatter radiation
Answer: B. Reduces beam intensity by half
Rationale: HVL measures beam quality and is the thickness of absorber
needed to reduce intensity to 50%.
3. Which interaction predominates for diagnostic x-rays in soft tissue
around 50 keV?
A. Photoelectric effect
B. Compton scattering
C. Pair production
D. Coherent scattering
Answer: B. Compton scattering
Rationale: In the diagnostic energy range, Compton interactions dominate
in soft tissue and are responsible for most scatter.
4. The SI unit of exposure is:
A. Gray
B. Sievert
C. Coulomb/kg
D. Roentgen
,Answer: C. Coulomb/kg
Rationale: Exposure is defined in terms of charge per mass of air, with the
SI unit being C/kg.
5. Which factor most strongly influences photoelectric absorption
probability?
A. Photon energy and atomic number
B. Density alone
C. Electron binding energy only
D. Tissue thickness
Answer: A. Photon energy and atomic number
Rationale: Photoelectric effect probability is proportional to Z³ and
inversely related to photon energy cubed.
6. In radiation protection, ALARA stands for:
A. As Low As Reasonably Achievable
B. As Little As Radiation Allowed
C. All Levels Are Regulated Always
D. Allowed Limits Are Reduced Annually
Answer: A. As Low As Reasonably Achievable
Rationale: ALARA is a guiding principle to minimize radiation exposure
while achieving clinical objectives.
7. Which dosimeter is most commonly used for personal monitoring of
occupational exposure?
, A. Ionization chamber
B. Thermoluminescent dosimeter
C. Geiger-Müller counter
D. Film badge
Answer: B. Thermoluminescent dosimeter
Rationale: TLDs are widely used for personnel monitoring due to accuracy,
reusability, and tissue-equivalent response.
8. The effective dose accounts for:
A. Only absorbed dose
B. Radiation weighting factors only
C. Tissue weighting and radiation weighting factors
D. Exposure time only
Answer: C. Tissue weighting and radiation weighting factors
Rationale: Effective dose (Sv) incorporates both radiation type and tissue
sensitivity.
9. What is the primary purpose of a flattening filter in a linear
accelerator?
A. Increase beam energy
B. Make the beam intensity uniform
C. Reduce electron contamination
D. Improve patient positioning
