Radiation Safety and Protection
Core concepts
Radiation protection rests on ALARA: reduce time, increase distance, and use appropriate shielding. Exposure follows the inverse-square law, so doubling distance from a point source reduces exposure rate to one-quarter. Occupational dose limits, public limits, fetal limits, and dose-rate limits are distinct; know which limit applies to a worker, a member of the public, a declared pregnant worker, and an embryo/fetus. Contamination control differs from external exposure: use gloves, absorbent materials, surveys, and proper waste decay. PET radionuclides emit 511 keV photons, so shielding and distance planning matter. Packages and areas require radiation surveys and wipe tests under applicable regulations.
Traps
Questions often mix units or confuse dose limits with dose-rate limits. Do not apply the public limit to an occupationally exposed worker, and do not assume lead is equally effective at all energies. Remember that dose badges measure occupational exposure but do not replace surveys. Pregnant patients and workers require careful counseling and protocol-specific instructions; the decision to perform a study is made with the ordering practitioner.
Worked example
A source produces 4 mR/h at 1 m. At 2 m, exposure is 4 × (1/2)² = 1 mR/h. At 0.5 m, it is 4 × (1/0.5)² = 16 mR/h. Rule of thumb: move away rather than rely only on shielding; small distance changes have large effects.