Radiation Protection, Safety and Dosimetry
Radiation Protection, Safety and Dosimetry
This domain tests dose limitation, shielding, collimation, personal monitoring, and practical ALARA decisions. Expect ICRP/AERB-style limits and inverse-square calculations.
Core rules
- ALARA: keep doses as low as reasonably achievable, social and economic factors considered.
- Occupational limit: 20 mSv/year averaged over five years, with no year above 50 mSv. Public limit: 1 mSv/year. Lens limit: 20 mSv/year. Declared pregnant worker: 1 mSv to the fetus.
- Use the shortest exposure, smallest field, greatest distance, and appropriate shielding. Lead aprons are commonly 0.25–0.5 mm Pb; check integrity.
- Collimate to the area of interest; shield gonads and thyroid when appropriate.
- Wear a personal dosimeter at collar or chest level as instructed; store away from the beam. TLD, OSL and film badges measure personal dose.
Worked example
A supervised area has 100 µSv/h at 1 m. At 2 m: 100 × (1/2)² = 25 µSv/h. At 4 m: 100 × (1/4)² = 6.25 µSv/h. Doubling distance quarters the dose rate; quadrupling distance reduces it sixteenfold.
Traps
- Confusing annual limit with a threshold below which no effect occurs.
- Mixing Gy (absorbed dose) and Sv (equivalent/effective dose).
- Wearing the badge under a lead apron without instruction.
- Leaving the collimator wide because the image looks better.