GXMO Radiation Physics and Safety 3 — Questions and Answers
Question 1: What is the annual occupational effective dose limit for radiation workers in the United States?
- 5 mSv (0.5 rem)
- 20 mSv (2 rem)
- 50 mSv (5 rem) (Correct answer)
- 100 mSv (10 rem)
Correct answer: 50 mSv (5 rem)
NCRP Report No. 116 sets the annual occupational effective dose limit at 50 mSv (5 rem) for radiation workers.
Question 2: Which type of radiation interaction results in a scattered photon with less energy than the incident photon and a recoil electron?
- Photoelectric effect
- Coherent (Rayleigh) scattering
- Compton scattering (Correct answer)
- Pair production
Correct answer: Compton scattering
In Compton scattering, the incident photon transfers part of its energy to a free or loosely bound outer-shell electron, scattering both the electron and a lower-energy photon.
Question 3: Which personal dosimeter provides the most accurate measurement of cumulative radiation dose over time?
- Survey meter
- Geiger-Müller counter
- Thermoluminescent dosimeter (TLD) (Correct answer)
- Ionization chamber survey meter
Correct answer: Thermoluminescent dosimeter (TLD)
TLDs store energy from ionizing radiation in crystal lattice traps and release it as light when heated, providing accurate cumulative dose measurements.
Question 4: What does the term 'inverse square law' describe in radiation physics?
- Dose increases proportionally with distance
- Dose rate is inversely proportional to the square of the distance from the source (Correct answer)
- Scatter increases with the square of field size
- Beam intensity doubles with each HVL
Correct answer: Dose rate is inversely proportional to the square of the distance from the source
The inverse square law states that radiation intensity is inversely proportional to the square of the distance from the source: doubling the distance reduces intensity to one-quarter.
Question 5: Which tissue type is considered most radiosensitive according to the law of Bergonié and Tribondeau?
- Nerve cells
- Muscle cells
- Rapidly dividing stem cells (Correct answer)
- Mature bone cells
Correct answer: Rapidly dividing stem cells
Bergonié and Tribondeau stated that cells are most radiosensitive when they are undifferentiated, rapidly dividing, and have a long mitotic future.
Question 6: What is the main biological effect of concern when a pregnant patient requires x-ray examination?
- Maternal cataracts
- Fetal bone hardening
- Stochastic effects on the developing embryo/fetus (Correct answer)
- Maternal hair loss
Correct answer: Stochastic effects on the developing embryo/fetus
The developing embryo/fetus is highly radiosensitive, and radiation exposure raises the stochastic risk of childhood cancer and potential deterministic effects depending on dose and gestational age.
Question 7: What is characteristic radiation?
- Radiation produced when electrons decelerate near a nucleus
- X-rays emitted when outer-shell electrons fill vacancies left by ejected inner-shell electrons (Correct answer)
- Radiation emitted by radioactive nuclei
- Scatter radiation from patient interactions
Correct answer: X-rays emitted when outer-shell electrons fill vacancies left by ejected inner-shell electrons
Characteristic radiation is produced when an outer-shell electron transitions to fill an inner-shell vacancy, releasing a photon with energy equal to the difference between the two shell binding energies.
GXMO Radiation Physics and Safety 3
What is the annual occupational effective dose limit for radiation workers in the United States?