CNMT Certified Nuclear Medicine Technologist Certification Exam
2026: Comprehensive Professional Practice Test — Radiation
Physics, Safety & Regulations, Radiopharmaceuticals,
Instrumentation, Quality Control & Clinical Procedures — 190
Multiple-Choice Questions with Answers & Detailed Rationales
Section I: Radiation Physics & Detection (Questions 1–13)
Question 1
A technologist is reviewing the properties of a radiopharmaceutical used for thyroid imaging.
The radionuclide emits gamma photons with an energy of 364 keV. Which of the following
best describes the interaction that predominates when these photons encounter a sodium
iodide crystal?
A. Photoelectric absorption
B. Compton scattering
C. Pair production
D. Coherent scattering
Correct Answer: A
Explanation: Photoelectric absorption predominates at diagnostic gamma energies in high-Z
detectors like NaI, enabling full-energy peak detection for spectroscopy.
Question 2
,During a quality control test on a dose calibrator, a technologist measures a Cs-137 source
and obtains a reading that is 15% lower than the expected value. Which of the following is
the most appropriate interpretation?
A. The source has decayed beyond its useful life
B. The dose calibrator may require recalibration or repair
C. The geometry of the source has changed
D. The constancy test has passed within acceptable limits
Correct Answer: B
Explanation: A deviation exceeding 10% on accuracy testing indicates the calibrator requires
service or recalibration per regulatory standards.
Question 3
Which of the following best explains why Tc-99m is the most widely used radionuclide in
diagnostic nuclear medicine?
A. It emits alpha particles that provide high therapeutic efficacy
B. Its 140 keV gamma emission is ideal for gamma camera detection
C. It has a physical half-life of 8 days allowing for extended storage
D. It is produced in a cyclotron for on-demand availability
Correct Answer: B
Explanation: Tc-99m's 140 keV photon energy optimally matches NaI crystal detection
efficiency while its 6-hour half-life minimizes patient dose.
,Question 4
A patient is injected with a radiopharmaceutical containing a small amount of Mo-99
breakthrough. Which of the following is the primary concern?
A. Reduced image resolution due to lower photon energy
B. Increased patient radiation dose from higher-energy photons
C. Chemical toxicity from molybdenum accumulation
D. Interference with radiochemical purity testing
Correct Answer: B
Explanation: Mo-99 breakthrough increases radiation burden because Mo-99 emits higher-
energy photons and has a longer half-life than Tc-99m.
Question 5
Which of the following statements correctly describes the relationship between energy
resolution and detector performance?
A. Better energy resolution means larger FWHM values
B. Energy resolution improves as the number of photoelectrons decreases
C. Better energy resolution allows more accurate discrimination of scattered photons
D. Energy resolution is independent of detector crystal thickness
Correct Answer: C
Explanation: Superior energy resolution produces narrower photopeaks, enabling tighter
energy windows that reject Compton-scattered events more effectively.
, Question 6
A technologist performs a Chi-square test on a well counter and obtains a value that exceeds
the critical value at the 95% confidence level. This finding indicates:
A. The counter is operating within acceptable statistical limits
B. The background count rate is too low for accurate measurement
C. The system exhibits non-random count variation requiring investigation
D. The detector crystal requires replacement
Correct Answer: C
Explanation: A Chi-square value exceeding the critical threshold indicates count variability
beyond Poisson statistics, suggesting equipment malfunction or environmental interference.
Question 7
Which of the following types of radiation detectors operates by collecting ion pairs produced
directly in a gas-filled chamber?
A. Sodium iodide scintillation detector
B. Geiger-Mueller counter
C. Semiconductor detector
D. Thermoluminescent dosimeter
Correct Answer: B
2026: Comprehensive Professional Practice Test — Radiation
Physics, Safety & Regulations, Radiopharmaceuticals,
Instrumentation, Quality Control & Clinical Procedures — 190
Multiple-Choice Questions with Answers & Detailed Rationales
Section I: Radiation Physics & Detection (Questions 1–13)
Question 1
A technologist is reviewing the properties of a radiopharmaceutical used for thyroid imaging.
The radionuclide emits gamma photons with an energy of 364 keV. Which of the following
best describes the interaction that predominates when these photons encounter a sodium
iodide crystal?
A. Photoelectric absorption
B. Compton scattering
C. Pair production
D. Coherent scattering
Correct Answer: A
Explanation: Photoelectric absorption predominates at diagnostic gamma energies in high-Z
detectors like NaI, enabling full-energy peak detection for spectroscopy.
Question 2
,During a quality control test on a dose calibrator, a technologist measures a Cs-137 source
and obtains a reading that is 15% lower than the expected value. Which of the following is
the most appropriate interpretation?
A. The source has decayed beyond its useful life
B. The dose calibrator may require recalibration or repair
C. The geometry of the source has changed
D. The constancy test has passed within acceptable limits
Correct Answer: B
Explanation: A deviation exceeding 10% on accuracy testing indicates the calibrator requires
service or recalibration per regulatory standards.
Question 3
Which of the following best explains why Tc-99m is the most widely used radionuclide in
diagnostic nuclear medicine?
A. It emits alpha particles that provide high therapeutic efficacy
B. Its 140 keV gamma emission is ideal for gamma camera detection
C. It has a physical half-life of 8 days allowing for extended storage
D. It is produced in a cyclotron for on-demand availability
Correct Answer: B
Explanation: Tc-99m's 140 keV photon energy optimally matches NaI crystal detection
efficiency while its 6-hour half-life minimizes patient dose.
,Question 4
A patient is injected with a radiopharmaceutical containing a small amount of Mo-99
breakthrough. Which of the following is the primary concern?
A. Reduced image resolution due to lower photon energy
B. Increased patient radiation dose from higher-energy photons
C. Chemical toxicity from molybdenum accumulation
D. Interference with radiochemical purity testing
Correct Answer: B
Explanation: Mo-99 breakthrough increases radiation burden because Mo-99 emits higher-
energy photons and has a longer half-life than Tc-99m.
Question 5
Which of the following statements correctly describes the relationship between energy
resolution and detector performance?
A. Better energy resolution means larger FWHM values
B. Energy resolution improves as the number of photoelectrons decreases
C. Better energy resolution allows more accurate discrimination of scattered photons
D. Energy resolution is independent of detector crystal thickness
Correct Answer: C
Explanation: Superior energy resolution produces narrower photopeaks, enabling tighter
energy windows that reject Compton-scattered events more effectively.
, Question 6
A technologist performs a Chi-square test on a well counter and obtains a value that exceeds
the critical value at the 95% confidence level. This finding indicates:
A. The counter is operating within acceptable statistical limits
B. The background count rate is too low for accurate measurement
C. The system exhibits non-random count variation requiring investigation
D. The detector crystal requires replacement
Correct Answer: C
Explanation: A Chi-square value exceeding the critical threshold indicates count variability
beyond Poisson statistics, suggesting equipment malfunction or environmental interference.
Question 7
Which of the following types of radiation detectors operates by collecting ion pairs produced
directly in a gas-filled chamber?
A. Sodium iodide scintillation detector
B. Geiger-Mueller counter
C. Semiconductor detector
D. Thermoluminescent dosimeter
Correct Answer: B
