Certified Nuclear Medicine Technologist (CNMT) Exam
2026/2027 | Complete Practice Test, Answers & Detailed
Explanations
DOMAIN I — RADIATION PHYSICS & DETECTION
Questions 1–21
1. Which particle has a negative charge and a mass approximately
equal to that of a proton?
A. Alpha particle
B. Beta-minus particle
C. Positron
D. Photon
Answer: B
Rationale: A beta-minus particle is an electron emitted from the
nucleus during beta-minus decay. It has a negative charge and a very
small mass compared with a proton, although the wording
“approximately equal” is imperfect; among the choices, beta-minus is
the correct nuclear electron. Photons have no mass or charge, while
alpha particles are helium nuclei.
2. What is the primary characteristic of a gamma ray?
A. It has a positive charge
B. It is a helium nucleus
,C. It is electromagnetic radiation
D. It is an electron
Answer: C
Rationale: Gamma rays are electromagnetic photons emitted from an
excited nucleus. They have no mass and no electrical charge.
3. During positron emission, a proton is converted into a:
A. Neutron
B. Photon
C. Beta-minus particle
D. Alpha particle
Answer: A
Rationale: In positron emission, a proton converts to a neutron while
emitting a positron and a neutrino. The atomic number decreases by
one while the mass number remains unchanged.
4. Which decay mode results in emission of an electron from the
nucleus?
A. Alpha decay
B. Beta-minus decay
C. Positron emission
D. Electron capture
Answer: B
,Rationale: Beta-minus decay converts a neutron into a proton and
emits an electron and antineutrino. This increases the atomic number
by one without changing the mass number.
5. Which radionuclide is commonly used for routine nuclear medicine
imaging because of its favorable 140-keV gamma emission?
A. Tc-99m
B. I-131
C. F-18
D. Sr-89
Answer: A
Rationale: Tc-99m emits a 140-keV gamma photon, which is well suited
to gamma-camera imaging. Its approximately six-hour physical half-life
also provides useful imaging while limiting prolonged radiation
exposure.
6. What is the physical half-life of a radionuclide?
A. Time required for all activity to disappear
B. Time required for activity to decrease by 25%
C. Time required for half the radioactive atoms to decay
D. Time required for the patient to eliminate half the activity
Answer: C
Rationale: Physical half-life is the time required for half of the
radioactive atoms in a sample to undergo radioactive decay.
, 7. A sample contains 80 mCi of a radionuclide with a 6-hour half-life.
Approximately how much remains after 12 hours?
A. 40 mCi
B. 20 mCi
C. 10 mCi
D. 5 mCi
Answer: C
Rationale: Twelve hours represents two half-lives. The activity changes
from 80 to 40 mCi after six hours and from 40 to 20 mCi after 12 hours.
Therefore, the correct answer is 20 mCi, making option B correct.
Correction: The calculation is 80 → 40 → 20 mCi.
Answer: B
8. What happens to radioactive activity after one physical half-life?
A. It doubles
B. It decreases to 75%
C. It decreases to 50%
D. It becomes zero
Answer: C
Rationale: By definition, one half-life reduces the number of radioactive
atoms and activity to approximately 50% of the original value.
2026/2027 | Complete Practice Test, Answers & Detailed
Explanations
DOMAIN I — RADIATION PHYSICS & DETECTION
Questions 1–21
1. Which particle has a negative charge and a mass approximately
equal to that of a proton?
A. Alpha particle
B. Beta-minus particle
C. Positron
D. Photon
Answer: B
Rationale: A beta-minus particle is an electron emitted from the
nucleus during beta-minus decay. It has a negative charge and a very
small mass compared with a proton, although the wording
“approximately equal” is imperfect; among the choices, beta-minus is
the correct nuclear electron. Photons have no mass or charge, while
alpha particles are helium nuclei.
2. What is the primary characteristic of a gamma ray?
A. It has a positive charge
B. It is a helium nucleus
,C. It is electromagnetic radiation
D. It is an electron
Answer: C
Rationale: Gamma rays are electromagnetic photons emitted from an
excited nucleus. They have no mass and no electrical charge.
3. During positron emission, a proton is converted into a:
A. Neutron
B. Photon
C. Beta-minus particle
D. Alpha particle
Answer: A
Rationale: In positron emission, a proton converts to a neutron while
emitting a positron and a neutrino. The atomic number decreases by
one while the mass number remains unchanged.
4. Which decay mode results in emission of an electron from the
nucleus?
A. Alpha decay
B. Beta-minus decay
C. Positron emission
D. Electron capture
Answer: B
,Rationale: Beta-minus decay converts a neutron into a proton and
emits an electron and antineutrino. This increases the atomic number
by one without changing the mass number.
5. Which radionuclide is commonly used for routine nuclear medicine
imaging because of its favorable 140-keV gamma emission?
A. Tc-99m
B. I-131
C. F-18
D. Sr-89
Answer: A
Rationale: Tc-99m emits a 140-keV gamma photon, which is well suited
to gamma-camera imaging. Its approximately six-hour physical half-life
also provides useful imaging while limiting prolonged radiation
exposure.
6. What is the physical half-life of a radionuclide?
A. Time required for all activity to disappear
B. Time required for activity to decrease by 25%
C. Time required for half the radioactive atoms to decay
D. Time required for the patient to eliminate half the activity
Answer: C
Rationale: Physical half-life is the time required for half of the
radioactive atoms in a sample to undergo radioactive decay.
, 7. A sample contains 80 mCi of a radionuclide with a 6-hour half-life.
Approximately how much remains after 12 hours?
A. 40 mCi
B. 20 mCi
C. 10 mCi
D. 5 mCi
Answer: C
Rationale: Twelve hours represents two half-lives. The activity changes
from 80 to 40 mCi after six hours and from 40 to 20 mCi after 12 hours.
Therefore, the correct answer is 20 mCi, making option B correct.
Correction: The calculation is 80 → 40 → 20 mCi.
Answer: B
8. What happens to radioactive activity after one physical half-life?
A. It doubles
B. It decreases to 75%
C. It decreases to 50%
D. It becomes zero
Answer: C
Rationale: By definition, one half-life reduces the number of radioactive
atoms and activity to approximately 50% of the original value.
