NRSB RMS cheat sheet

Radon Measurement Fundamentals and Physics

• Radon-222 is a noble gas produced by alpha decay of radium-226; its half-life is 3.82 days, and it decays by alpha emission to polonium-218.

• The short-lived progeny (Po-218, Pb-214, Bi-214, Po-214) reach secular equilibrium with radon in about 3–4 hours in a closed environment; equilibrium fraction F is the ratio of progeny activity to radon activity.

• Radon activity concentration is expressed in becquerels per cubic meter (Bq/m³) or picocuries per liter (pCi/L); 1 pCi/L = 37 Bq/m³.

• Working level (WL) is defined as any combination of short-lived progeny in 1 L of air that emits 1.3 × 10^5 MeV of alpha energy; 1 WL = 100 pCi/L of radon at 100% equilibrium (F = 1.0).

• Exposure to 1 WL for 170 hours equals 1 working level month (WLM); annual dose conversion uses WLM and the equilibrium fraction of the measured radon.

• Radon transport into buildings is driven by pressure-driven soil gas entry (stack effect, exhaust fans, wind), diffusion, and emanation from building materials; pressure-driven flow dominates in most homes.

• The equilibrium fraction F is typically 0.3–0.7 indoors and depends on ventilation rate, aerosol concentration, and plate-out; it must be measured or assumed when converting radon concentration to WL or dose.

• Alpha track detectors, electret ion chambers, and continuous radon monitors measure radon gas; charcoal canisters and alpha scintillation cells measure radon or progeny by different collection principles.