Radiation Protection and Safety
What this domain tests
Radiation Protection and Safety tests dose quantities, limits, ALARA, shielding, distance and monitoring. For Category 2 radiography, you must be able to choose the right limit, calculate a practical exposure control, and explain why a measured dose rate, not a nominal one, drives decisions.
Core rules
- Occupational effective dose limit is 20 mSv per year averaged over five years, with no more than 50 mSv in any single year; the public limit is 1 mSv per year. National values may differ, so use the exam stated values.
- Use time, distance and shielding in that order of practicality. Dose rate from a point source falls with the inverse square of distance.
- Shielding calculations use half-value layers (HVL) or tenth-value layers (TVL); for a given material, dose rate after shielding is initial rate divided by 2 raised to thickness divided by HVL.
- Personal dosimeters are legal records; survey meters are operational controls. Neither replaces a proper barrier and supervision.
- ALARA requires dose constraints and optimization, not just compliance with limits.
Worked example
An Ir-192 source gives 800 µSv/h at 1 m. You need a boundary at 7.5 µSv/h. Using inverse square: D1d1 squared equals D2d2 squared, so d2 = 1 times sqrt(800 divided by 7.5) = 10.3 m. If a 20 mm steel barrier is added and steel HVL for Ir-192 is about 13 mm, attenuation is 2 raised to 20 divided by 13, about 2.9; the distance can then be reduced accordingly. State assumptions because HVL changes with energy and geometry.
Traps
Using the public limit for a classified worker; mixing µSv/h and mSv/h; forgetting source decay; treating a dosimeter as an area monitor; ignoring scatter from walls and floor.