ABR Medical Physics Certification
Examination Practice Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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1. What is the primary interaction of diagnostic x-rays in soft tissue at
energies of 20–120 keV?
A. Pair production
B. Compton scattering
C. Photoelectric effect
D. Coherent scattering
Answer: Photoelectric effect
Rationale: At diagnostic energies, the photoelectric effect dominates in soft
tissue due to its higher atomic number dependence and energy range
sensitivity.
, 2. The half-value layer (HVL) of an x-ray beam is used to determine:
A. Beam intensity at a point
B. Beam quality (penetrating ability)
C. Scatter fraction
D. Tube loading
Answer: Beam quality (penetrating ability)
Rationale: HVL is the thickness of material required to reduce the x-ray
intensity by half, reflecting beam energy and quality.
3. Which detector type provides the highest spatial resolution in
diagnostic radiography?
A. Photodiode
B. Film-screen system
C. Ionization chamber
D. Scintillator
Answer: Film-screen system
Rationale: Traditional film-screen systems have finer granularity compared
to digital detectors, offering superior spatial resolution.
4. The energy of a photon is directly proportional to:
A. Wavelength
, B. Frequency
C. Mass
D. Intensity
Answer: Frequency
Rationale: Photon energy is given by E = hf, showing direct proportionality to
frequency.
5. Which of the following imaging modalities exposes the patient to the
highest average radiation dose?
A. Chest radiography
B. CT abdomen/pelvis
C. Mammography
D. Fluoroscopy
Answer: CT abdomen/pelvis
Rationale: CT scans, particularly of large regions like the abdomen/pelvis,
deliver much higher doses than plain radiography or mammography.
6. In radiation therapy, which quantity measures the energy deposited
per unit mass of tissue?
A. Fluence
B. Exposure
, C. Absorbed dose
D. Kerma
Answer: Absorbed dose
Rationale: Absorbed dose (Gy) represents energy per unit mass absorbed in
tissue, critical for therapeutic planning.
7. Compton scattering probability increases with:
A. Higher atomic number
B. Higher photon energy
C. Lower photon energy
D. Higher electron binding energy
Answer: Higher photon energy
Rationale: Compton scattering dominates at intermediate energies and
increases with photon energy and electron density, but is less dependent on
atomic number.
8. What is the main purpose of a bowtie filter in CT imaging?
A. Increase mAs
B. Reduce patient dose and improve image uniformity
C. Increase kVp
D. Filter scattered radiation only
Examination Practice Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary interaction of diagnostic x-rays in soft tissue at
energies of 20–120 keV?
A. Pair production
B. Compton scattering
C. Photoelectric effect
D. Coherent scattering
Answer: Photoelectric effect
Rationale: At diagnostic energies, the photoelectric effect dominates in soft
tissue due to its higher atomic number dependence and energy range
sensitivity.
, 2. The half-value layer (HVL) of an x-ray beam is used to determine:
A. Beam intensity at a point
B. Beam quality (penetrating ability)
C. Scatter fraction
D. Tube loading
Answer: Beam quality (penetrating ability)
Rationale: HVL is the thickness of material required to reduce the x-ray
intensity by half, reflecting beam energy and quality.
3. Which detector type provides the highest spatial resolution in
diagnostic radiography?
A. Photodiode
B. Film-screen system
C. Ionization chamber
D. Scintillator
Answer: Film-screen system
Rationale: Traditional film-screen systems have finer granularity compared
to digital detectors, offering superior spatial resolution.
4. The energy of a photon is directly proportional to:
A. Wavelength
, B. Frequency
C. Mass
D. Intensity
Answer: Frequency
Rationale: Photon energy is given by E = hf, showing direct proportionality to
frequency.
5. Which of the following imaging modalities exposes the patient to the
highest average radiation dose?
A. Chest radiography
B. CT abdomen/pelvis
C. Mammography
D. Fluoroscopy
Answer: CT abdomen/pelvis
Rationale: CT scans, particularly of large regions like the abdomen/pelvis,
deliver much higher doses than plain radiography or mammography.
6. In radiation therapy, which quantity measures the energy deposited
per unit mass of tissue?
A. Fluence
B. Exposure
, C. Absorbed dose
D. Kerma
Answer: Absorbed dose
Rationale: Absorbed dose (Gy) represents energy per unit mass absorbed in
tissue, critical for therapeutic planning.
7. Compton scattering probability increases with:
A. Higher atomic number
B. Higher photon energy
C. Lower photon energy
D. Higher electron binding energy
Answer: Higher photon energy
Rationale: Compton scattering dominates at intermediate energies and
increases with photon energy and electron density, but is less dependent on
atomic number.
8. What is the main purpose of a bowtie filter in CT imaging?
A. Increase mAs
B. Reduce patient dose and improve image uniformity
C. Increase kVp
D. Filter scattered radiation only
