NRSB RMT cheat sheet

Radon Measurement Fundamentals and Testing Practice

• Radon-222 is a noble gas produced in the uranium-238 decay chain (Ra-226 → Rn-222, half-life 3.82 days); its short-lived progeny Po-218, Pb-214, Bi-214, and Po-214 emit the alpha and gamma radiation most detectors count.

• Units: 1 pCi/L = 37 Bq/m³; working level (WL) = any combination of short-lived progeny in 1 L of air with 1.3 × 10^5 MeV of potential alpha energy; 1 WL ≈ 200 pCi/L at 50% equilibrium; EPA action level is 4 pCi/L (≈148 Bq/m³).

• Equilibrium ratio F = actual PAEC ÷ PAEC at full equilibrium; F in homes typically 0.3–0.7; a detector that counts only progeny (e.g., charcoal or electret alpha track) must apply F to report gas concentration, while an ionization chamber measures gas directly.

• Short-term tests: charcoal adsorption canisters (2–7 days, exposed 48–96 h, analyzed by gamma spectroscopy of Pb-214/Bi-214), liquid scintillation vials, and electret ion chambers; results are influenced by temperature, humidity, and barometric swings during exposure.

• Long-term tests: alpha-track detectors (CR-39 or LR-115) and electret ion chambers exposed 90 days to 1 year; alpha tracks come from Rn-222 and Po-218 deposited on the detector, so they integrate seasonal variation and are the basis for deciding mitigation.

• Closed-house conditions before and during a short-term test: doors and windows closed 12 hours before deployment and throughout; heating/cooling may run normally; permanent vents and fans that exhaust house air are not operated except as required; do not test during severe storms.

• Placement rules: lowest livable level of the home; 20 inches (50 cm) above the floor, at least 4 inches (10 cm) from other objects, at least 3 feet (0.9 m) from exterior doors, windows, and air-supply registers; do not place in bathrooms, kitchens, laundry rooms, closets, crawl spaces, or hallways.

• Quality assurance: each measurement device type requires calibration traceable to a national standard, annual performance tests (spikes and blanks), duplicate measurements in at least 10% of locations, and routine background and efficiency checks; devices with known bias must be corrected or removed.

• Reporting: results in pCi/L with the analytical uncertainty stated; follow-up action is indicated at or above 4 pCi/L, and a confirmatory measurement (long-term or a second short-term test under closed conditions) is standard practice before committing to mitigation.