FRCR FRCR Radiation Physics and Dosimetry 1 — Questions and Answers
Question 1: Which unit is used to express absorbed radiation dose in the SI system?
- Gray (Gy) (Correct answer)
- Sievert (Sv)
- Roentgen (R)
- Becquerel (Bq)
Correct answer: Gray (Gy)
The Gray (Gy) is the SI unit of absorbed dose, defined as 1 joule of energy deposited per kilogram of tissue.
Question 2: What does the radiation weighting factor (wR) account for when calculating equivalent dose?
- Biological effectiveness of different radiation types (Correct answer)
- Energy of the radiation beam
- Distance from the radiation source
- Density of the irradiated tissue
Correct answer: Biological effectiveness of different radiation types
The radiation weighting factor adjusts for the relative biological effectiveness of different types of ionizing radiation when calculating equivalent dose in Sieverts.
Question 3: Which of the following best describes the half-value layer (HVL) of an X-ray beam?
- Thickness of material that reduces beam intensity by 50% (Correct answer)
- Depth at which dose is half of the surface dose
- Distance at which the dose rate is halved
- Layer of tissue absorbing half the photon energy
Correct answer: Thickness of material that reduces beam intensity by 50%
The HVL is the thickness of a specified material required to reduce the X-ray beam intensity (or air kerma rate) to exactly half its original value.
Question 4: In X-ray production, which interaction is primarily responsible for the continuous bremsstrahlung spectrum?
- Deceleration of electrons in the Coulomb field of nuclei (Correct answer)
- Photoelectric absorption by target atoms
- Compton scattering of electrons
- Pair production in the target material
Correct answer: Deceleration of electrons in the Coulomb field of nuclei
Bremsstrahlung ('braking radiation') is produced when high-speed electrons are decelerated by the strong electric field of target nuclei, emitting X-ray photons with a continuous energy spectrum.
Question 5: What is the primary purpose of added filtration in a diagnostic X-ray tube?
- Remove low-energy photons to reduce patient skin dose (Correct answer)
- Increase the overall intensity of the X-ray beam
- Sharpen image resolution by collimating the beam
- Reduce characteristic radiation from the target
Correct answer: Remove low-energy photons to reduce patient skin dose
Added filtration (typically aluminum) preferentially attenuates low-energy photons that would be absorbed by the patient's skin without contributing to image formation.
Question 6: Which quantity is used to express the stochastic radiation risk to a whole organism accounting for tissue sensitivity?
- Effective dose (Sieverts) (Correct answer)
- Absorbed dose (Gray)
- Equivalent dose (Sieverts)
- Air kerma (Gray)
Correct answer: Effective dose (Sieverts)
Effective dose uses tissue weighting factors (wT) to sum equivalent doses across all irradiated organs, giving a single value proportional to overall stochastic risk.
FRCR FRCR Radiation Physics and Dosimetry 1
Which unit is used to express absorbed radiation dose in the SI system?