NMTCB Exam Prep 2026/2027 | Nuclear Medicine,
Radiopharmacy, Instrumentation, Radiation Safety & Clinical
Procedures
DOMAIN I — RADIATION PHYSICS & DETECTION
Questions 1–21
1.
Which type of radioactive decay results in the emission of a positron?
A. Alpha decay
B. Beta-minus decay
C. Beta-plus decay
D. Gamma decay
Answer: C. Beta-plus decay
Rationale: Positron emission occurs when a proton changes into a
neutron while emitting a positron and neutrino.
2.
A radionuclide has a physical half-life of 6 hours. If the initial activity is
80 mCi, approximately how much remains after 18 hours?
A. 40 mCi
B. 20 mCi
C. 10 mCi
D. 5 mCi
,Answer: C. 10 mCi
Rationale: Eighteen hours equals three half-lives: 80 → 40 → 20 → 10
mCi.
3.
Which radiation has the greatest penetrating ability?
A. Alpha particles
B. Beta particles
C. Gamma photons
D. Electrons
Answer: C. Gamma photons
Rationale: Gamma photons are highly penetrating electromagnetic
radiation compared with alpha and beta particles.
4.
What is the primary interaction responsible for producing scattered
photons in many nuclear medicine imaging situations?
A. Pair production
B. Compton scattering
C. Photodisintegration
D. Annihilation
Answer: B. Compton scattering
Rationale: Compton interactions produce scattered photons that can
degrade nuclear medicine image quality.
,5.
The energy of a photon is inversely related to its:
A. Frequency
B. Velocity
C. Wavelength
D. Amplitude
Answer: C. Wavelength
Rationale: Photon energy is inversely proportional to wavelength and
directly proportional to frequency.
6.
What happens during positron-electron annihilation?
A. Two gamma photons are produced at approximately 511 keV each
B. One 140-keV photon is produced
C. An alpha particle is emitted
D. A beta-minus particle is emitted
Answer: A. Two gamma photons are produced at approximately 511
keV each
Rationale: A positron annihilates with an electron, producing two 511-
keV photons traveling approximately 180° apart.
7.
, The SI unit of radioactive activity is:
A. Gray
B. Sievert
C. Becquerel
D. Coulomb
Answer: C. Becquerel
Rationale: The becquerel represents one nuclear transformation per
second.
8.
Which unit is traditionally used to describe absorbed radiation dose?
A. Gray
B. Becquerel
C. Curie
D. Roentgen
Answer: A. Gray
Rationale: The gray is the SI unit of absorbed dose and equals one joule
per kilogram.
9.
A sample contains 32 mCi of a radionuclide with a 2-hour half-life. What
activity remains after 6 hours?
A. 16 mCi
B. 8 mCi
Radiopharmacy, Instrumentation, Radiation Safety & Clinical
Procedures
DOMAIN I — RADIATION PHYSICS & DETECTION
Questions 1–21
1.
Which type of radioactive decay results in the emission of a positron?
A. Alpha decay
B. Beta-minus decay
C. Beta-plus decay
D. Gamma decay
Answer: C. Beta-plus decay
Rationale: Positron emission occurs when a proton changes into a
neutron while emitting a positron and neutrino.
2.
A radionuclide has a physical half-life of 6 hours. If the initial activity is
80 mCi, approximately how much remains after 18 hours?
A. 40 mCi
B. 20 mCi
C. 10 mCi
D. 5 mCi
,Answer: C. 10 mCi
Rationale: Eighteen hours equals three half-lives: 80 → 40 → 20 → 10
mCi.
3.
Which radiation has the greatest penetrating ability?
A. Alpha particles
B. Beta particles
C. Gamma photons
D. Electrons
Answer: C. Gamma photons
Rationale: Gamma photons are highly penetrating electromagnetic
radiation compared with alpha and beta particles.
4.
What is the primary interaction responsible for producing scattered
photons in many nuclear medicine imaging situations?
A. Pair production
B. Compton scattering
C. Photodisintegration
D. Annihilation
Answer: B. Compton scattering
Rationale: Compton interactions produce scattered photons that can
degrade nuclear medicine image quality.
,5.
The energy of a photon is inversely related to its:
A. Frequency
B. Velocity
C. Wavelength
D. Amplitude
Answer: C. Wavelength
Rationale: Photon energy is inversely proportional to wavelength and
directly proportional to frequency.
6.
What happens during positron-electron annihilation?
A. Two gamma photons are produced at approximately 511 keV each
B. One 140-keV photon is produced
C. An alpha particle is emitted
D. A beta-minus particle is emitted
Answer: A. Two gamma photons are produced at approximately 511
keV each
Rationale: A positron annihilates with an electron, producing two 511-
keV photons traveling approximately 180° apart.
7.
, The SI unit of radioactive activity is:
A. Gray
B. Sievert
C. Becquerel
D. Coulomb
Answer: C. Becquerel
Rationale: The becquerel represents one nuclear transformation per
second.
8.
Which unit is traditionally used to describe absorbed radiation dose?
A. Gray
B. Becquerel
C. Curie
D. Roentgen
Answer: A. Gray
Rationale: The gray is the SI unit of absorbed dose and equals one joule
per kilogram.
9.
A sample contains 32 mCi of a radionuclide with a 2-hour half-life. What
activity remains after 6 hours?
A. 16 mCi
B. 8 mCi
