Radon Measurement Fundamentals and Testing Practice
What this domain covers
The RMT measurement domain tests radon fundamentals, device selection, closed-house testing, placement, QA/QC, and reporting. Expect practical items: which device fits the duration and site, whether a result is valid, and how to convert and interpret it.
Core rules and concepts
- Radon-222 is a noble gas with a 3.82-day half-life. It decays by alpha emission; the short-lived progeny (Po-218, Pb-214, Bi-214, Po-214) deliver most of the lung dose.
- Report in pCi/L or Bq/m³. 1 pCi/L = 37 Bq/m³. EPA's action level is 4 pCi/L; consider action at 2 pCi/L.
- Short-term tests run 2–90 days; long-term tests exceed 90 days. Charcoal adsorption and liquid scintillation devices are typically exposed 2–7 days. Alpha-track detectors run 1–12 months. Electret ion chambers and continuous radon monitors can provide short-term results; a CRM used for a real-estate test should run at least 48 hours.
- For short-term tests, maintain closed-house conditions: keep doors and windows closed and stop fans or other air movement for 12 hours before and during the test. Test the lowest livable level.
- Place the device in a central location, 2–7 ft above the floor, away from exterior walls, drafts, heat, humidity, and bathrooms/kitchens.
- QA/QC includes calibration, duplicates, blanks, spikes, and chain-of-custody; follow the manufacturer and ANSI/AARST MS-QA.
Worked example
A 48-hour CRM in a basement averages 4.4 pCi/L. Convert: 4.4 × 37 = 163 Bq/m³. Because the result is above 4 pCi/L but below 10 pCi/L, EPA guidance calls for a confirmatory short-term test (or a long-term test) before deciding on mitigation. The reasoning: one short-term result is screening, not a final exposure estimate.
Traps that cost marks
- Treating a single charcoal result as definitive.
- Starting the test before 12 hours of closed-house conditions.
- Placing a detector near a draft, sump, or exterior wall.
- Mixing pCi/L and Bq/m³.
- Skipping CRM calibration or tamper checks.