FRCR FRCR Physics and Radiation Safety 1 — Questions and Answers
Question 1: What is the unit of absorbed radiation dose in the SI system?
- Gray (Gy) (Correct answer)
- Sievert (Sv)
- Becquerel (Bq)
- Roentgen (R)
Correct answer: Gray (Gy)
The Gray (Gy) is the SI unit of absorbed dose, defined as one joule of energy deposited per kilogram of tissue.
Question 2: Which interaction between X-rays and matter is most important for diagnostic imaging in soft tissue at typical diagnostic energies?
- Compton scattering (Correct answer)
- Photoelectric effect
- Pair production
- Coherent scattering
Correct answer: Compton scattering
Compton scattering dominates in soft tissue at diagnostic X-ray energies (above ~30 keV), producing scattered photons that degrade image contrast.
Question 3: What does the term 'half-value layer' (HVL) describe in radiology?
- Thickness of material reducing beam intensity by 50% (Correct answer)
- Half-life of a radionuclide
- Depth at which dose is halved in a patient
- Distance at which dose rate halves
Correct answer: Thickness of material reducing beam intensity by 50%
The half-value layer is the thickness of a specified material required to reduce the intensity of an X-ray beam to half its original value.
Question 4: Which type of radiation has the highest linear energy transfer (LET)?
- Alpha particles (Correct answer)
- Beta particles
- X-rays
- Gamma rays
Correct answer: Alpha particles
Alpha particles are large, doubly charged, and deposit energy densely along a short track, giving them the highest LET.
Question 5: In CT dosimetry, what does CTDI (Computed Tomography Dose Index) measure?
- Average dose delivered along the scan axis (Correct answer)
- Effective dose to the whole body
- Organ dose to a specific structure
- Surface entrance dose
Correct answer: Average dose delivered along the scan axis
CTDI represents the average dose profile along the z-axis for a standardized CT acquisition, measured in phantoms with ionization chambers.
Question 6: Which legislation governs radiation protection in medical exposures in the US?
- NRC regulations (10 CFR) (Correct answer)
- ALARA directive
- ICRP Publication 103
- EURATOM BSS Directive
Correct answer: NRC regulations (10 CFR)
The US Nuclear Regulatory Commission (NRC) issues 10 CFR regulations governing occupational and medical radiation exposure.
FRCR FRCR Physics and Radiation Safety 1
What is the unit of absorbed radiation dose in the SI system?