DRC Radiologic Physics & Safety 2 — Questions and Answers
Question 1: Which unit of radiation dose equivalent is used to express occupational exposure limits in the United States?
- Gray (Gy)
- Sievert (Sv) (Correct answer)
- Roentgen (R)
- Coulomb per kilogram (C/kg)
Correct answer: Sievert (Sv)
The sievert (Sv) is the SI unit for dose equivalent, accounting for biological effectiveness, and is used in occupational exposure limits.
Question 2: What is the maximum permissible dose (MPD) for a radiation worker per year according to NCRP recommendations?
- 5 mSv (0.5 rem)
- 50 mSv (5 rem) (Correct answer)
- 100 mSv (10 rem)
- 500 mSv (50 rem)
Correct answer: 50 mSv (5 rem)
The NCRP recommends a maximum permissible dose of 50 mSv (5 rem) per year for occupationally exposed individuals.
Question 3: The penumbra effect in dental radiography refers to:
- Overexposure of the receptor
- A blurred unsharp border around the image (Correct answer)
- Increased contrast at image edges
- Elongation of the radiographic image
Correct answer: A blurred unsharp border around the image
Penumbra is the zone of unsharpness at image edges caused by the finite size of the focal spot.
Question 4: Which interaction between X-rays and matter is primarily responsible for image formation on dental radiographs?
- Pair production
- Photoelectric effect (Correct answer)
- Thompson scattering
- Bremsstrahlung radiation
Correct answer: Photoelectric effect
The photoelectric effect, where photons are completely absorbed by inner-shell electrons, is the primary interaction responsible for radiographic image contrast.
Question 5: A film badge worn by dental personnel measures:
- Only gamma radiation exposure
- Cumulative occupational radiation exposure over time (Correct answer)
- Instantaneous dose rate only
- Patient dose during procedures
Correct answer: Cumulative occupational radiation exposure over time
Film badges record cumulative radiation exposure over a monitoring period, typically one to three months, for occupational dose tracking.
Question 6: Which type of radiation is most easily stopped by a sheet of paper?
- X-rays
- Gamma rays
- Beta particles
- Alpha particles (Correct answer)
Correct answer: Alpha particles
Alpha particles, having the largest mass and charge, are the least penetrating and are stopped by a sheet of paper or a few centimeters of air.
Question 7: The concept of ALARA in radiation protection stands for:
- Absorbed Level At Reasonable Adjustment
- As Low As Reasonably Achievable (Correct answer)
- Allowable Limit After Radiation Assessment
- Authorized Level for Annual Radiation Activity
Correct answer: As Low As Reasonably Achievable
ALARA means keeping radiation exposure As Low As Reasonably Achievable, balancing benefits against economic and social factors.
DRC Radiologic Physics & Safety 2
Which unit of radiation dose equivalent is used to express occupational exposure limits in the United States?