Radiation Protection and Health Physics
Core concepts
Master dose quantities: absorbed dose (Gy), equivalent dose (Sv), and effective dose, plus the weighting factors that connect them. Know the inverse-square law, half-value layer (HVL) and tenth-value layer (TVL), and the difference between external and internal exposure. Understand time, distance, and shielding as the three controls for external dose, and the concepts of committed dose, annual limits, and dose constraints. Be familiar with contamination surveys, smear vs direct surveys, and the distinction between contamination and radiation.
Common traps
Questions often confuse dose rate with dose, or use the wrong weighting factor for alpha particles (20) vs photons (1). Watch for mixing HVL and TVL - HVL reduces intensity by half, TVL by a factor of ten. Another trap: assuming alpha emitters are a major external hazard (they are not; they matter internally). Be careful with units: 1 Sv = 100 rem, and mSv vs µSv errors are common.
Worked example / rule of thumb
Rule of thumb: after n half-value layers, intensity is I₀/2ⁿ. For a 100 mSv/h field behind 3 HVLs, dose rate = 100/8 = 12.5 mSv/h. For distance, doubling distance quarters the dose rate (inverse square).
Study tip
Keep a small conversion card: 1 Sv = 100 rem, 1 Gy = 100 rad, 1 mSv = 100 mrem. Most calculation errors are unit errors, not physics errors.