RSO Radiation Sources and Equipment Safety 2 — Questions and Answers
Question 1: The inverse square law states that radiation intensity from a point source varies with distance by:
- Decreasing linearly with distance
- Decreasing proportionally to the square of the distance (Correct answer)
- Decreasing exponentially with distance
- Remaining constant until reaching the beam boundary
Correct answer: Decreasing proportionally to the square of the distance
The inverse square law states that radiation intensity from a point source decreases by the square of the distance: if you double the distance, intensity decreases to one-quarter the original value.
Question 2: Which shielding material is most appropriate for attenuating high-energy gamma radiation in a radiology facility?
- Polyethylene (plastic)
- Lead or concrete (Correct answer)
- Aluminum
- Water only
Correct answer: Lead or concrete
High-density, high-atomic-number materials like lead and concrete are most effective for attenuating gamma radiation because photoelectric absorption and Compton scattering cross sections favor these materials.
Question 3: A survey meter reads zero after entering a high-dose-rate area. The RSO should suspect the detector is:
- Working correctly—no radiation is present
- In saturation ('pinned') due to excessive dose rate overwhelming the detector electronics (Correct answer)
- Calibrated in the wrong units
- Out of battery
Correct answer: In saturation ('pinned') due to excessive dose rate overwhelming the detector electronics
Many ionization chamber and GM detectors can saturate or peg at full scale and then read zero ('pegged and stuck') at extremely high dose rates; this is a known detector failure mode in high-radiation fields.
Question 4: The half-value layer (HVL) for a specific radiation/shielding combination is the thickness of material required to:
- Reduce radiation intensity by 50% (Correct answer)
- Reduce radiation intensity by 90%
- Absorb all radiation
- Reduce dose rate to background levels
Correct answer: Reduce radiation intensity by 50%
The half-value layer (HVL) is defined as the thickness of a specific shielding material that reduces the incident radiation intensity by 50% (one-half).
Question 5: A high-radiation area requiring a locked door or other physical controls is defined under NRC regulations where doses could exceed:
- 0.05 mSv/h (5 mrem/h)
- 1 mSv/h (100 mrem/h) (Correct answer)
- 10 mSv/h (1,000 mrem/h)
- 50 mSv/h (5,000 mrem/h)
Correct answer: 1 mSv/h (100 mrem/h)
Under 10 CFR 20.1601, a High Radiation Area is where dose rates could exceed 1 mSv/h (100 mrem/h) at 30 cm, requiring control measures such as locked access or continuous attended entry.
Question 6: Criticality safety is primarily a concern for RSOs working at facilities that handle:
- Any sealed gamma source above 1 Curie
- Fissile materials such as enriched uranium or plutonium in sufficient quantities (Correct answer)
- High-energy X-ray equipment above 500 kVp
- Naturally occurring radioactive materials (NORM)
Correct answer: Fissile materials such as enriched uranium or plutonium in sufficient quantities
Criticality concerns arise when fissile material (e.g., U-235, Pu-239) could accumulate in sufficient geometry and quantity to sustain a self-sustaining nuclear chain reaction, which can occur in fuel processing or research facilities.
RSO Radiation Sources and Equipment Safety 2
The inverse square law states that radiation intensity from a point source varies with distance by: