ARRT Radiation Physics and Radiobiology 3 — Questions and Answers
Question 1: Characteristic radiation is produced when an outer-shell electron fills a vacancy in which shell?
- Valence shell only
- An inner electron shell (Correct answer)
- The conduction band
- The M shell exclusively
Correct answer: An inner electron shell
Characteristic radiation is emitted when an outer-shell electron transitions to fill a vacancy in an inner shell, releasing a photon with energy equal to the difference between the two shells.
Question 2: The relative biologic effectiveness (RBE) of alpha particles compared to x-rays is approximately:
- 1
- 5
- 20 (Correct answer)
- 100
Correct answer: 20
Alpha particles have an RBE of approximately 20, meaning they are 20 times more biologically effective than x-rays at causing the same level of damage.
Question 3: During which phase of the cell cycle are cells MOST radiosensitive?
- S phase (DNA synthesis)
- G1 phase
- M phase (mitosis) (Correct answer)
- G2 phase
Correct answer: M phase (mitosis)
Cells are most radiosensitive during M phase because chromosomes are condensed and the mitotic spindle is vulnerable to radiation-induced disruption.
Question 4: What is bremsstrahlung radiation?
- Radiation emitted during nuclear fission
- X-rays produced when electrons decelerate near a nucleus (Correct answer)
- Gamma rays from isomeric transition
- Photons produced during pair production annihilation
Correct answer: X-rays produced when electrons decelerate near a nucleus
Bremsstrahlung ('braking radiation') is produced when high-speed electrons lose kinetic energy by decelerating in the Coulomb field of a nucleus, emitting photons with a continuous energy spectrum.
Question 5: Which statement about the photoelectric effect is correct?
- It predominates at high photon energies above 1.02 MeV
- The ejected electron carries away all of the photon's energy minus binding energy (Correct answer)
- It requires photon energy less than the electron's binding energy
- It occurs primarily in low atomic number materials
Correct answer: The ejected electron carries away all of the photon's energy minus binding energy
In the photoelectric effect, the incident photon is completely absorbed and a photoelectron is ejected with kinetic energy equal to the photon energy minus the electron's binding energy.
Question 6: Half-value layer (HVL) is defined as the thickness of material that reduces radiation intensity by:
- 25%
- 50% (Correct answer)
- 75%
- 90%
Correct answer: 50%
HVL is the thickness of an absorber required to reduce the incident radiation intensity to exactly one-half (50%) of its original value.
Question 7: Which cellular lesion produced by ionizing radiation is considered MOST critical for cell killing?
- Single-strand DNA break
- Protein denaturation
- Double-strand DNA break (Correct answer)
- Mitochondrial membrane damage
Correct answer: Double-strand DNA break
Double-strand DNA breaks (DSBs) are the most lethal radiation-induced lesion because they are difficult to repair accurately and can lead to chromosomal aberrations and cell death.
ARRT Radiation Physics and Radiobiology 3
Characteristic radiation is produced when an outer-shell electron fills a vacancy in which shell?