Fundamentals of Radiation Physics and Radioactivity
Core concepts
Candidates must be fluent in atomic structure, the distinction between ionizing and non-ionizing radiation, and the modes of radioactive decay. Know alpha, beta-minus, beta-plus, electron capture, and isomeric transition (gamma emission), and how each changes Z and A. Understand activity (becquerel = 1 decay/s; curie = 3.7×10^10 Bq), half-life, and the decay equation A = A0·e^(−λt) with λ = ln2/T½. Distinguish physical half-life from biological and effective half-life (1/Teff = 1/Tphys + 1/Tbio). Photon interactions-photoelectric, Compton, pair production-and their Z- and energy-dependence are heavily tested.
Traps
Questions often swap activity for dose, or ask which quantity is conserved in a decay (nucleon number, charge). Watch unit conversions (mCi to MBq: 1 mCi = 37 MBq) and the difference between exposure (C/kg), absorbed dose (Gy), and equivalent dose (Sv). Beta-plus decay produces annihilation photons (511 keV); don't confuse with gamma emission. Remember the photoelectric effect dominates at low energy and high Z, while Compton dominates at diagnostic energies in soft tissue.
Worked example / rule of thumb
A source has T½ = 6 h. After 24 h (4 half-lives), activity = A0/2^4 = A0/16, about 6.25% remaining. Rule of thumb: count half-lives, then divide by 2^n-no exponential math needed.