Measurement
Annual average concentration
The radon concentration averaged over a full year, the quantity to which most reference levels formally apply. It is estimated from long-term measurements, sometimes adjusted with seasonal correction factors.
Related terms
Radon testingThe process of measuring the radon concentration in indoor air with a detector. Because levels vary greatly between buildings — even neighbouring ones — testing is the only way to know the level of a specific home or workplace.Passive detectorA radon detector with no power supply or moving parts, such as alpha-track or electret detectors. It is left in place for weeks or months and then analysed in a laboratory, making it the usual choice for the long-term measurements regulations rely on.Alpha-track detectorA passive detector containing a small piece of plastic that alpha particles from radon decay mark with microscopic tracks. After an exposure of one to twelve months, a laboratory counts the tracks to calculate the average radon concentration.Electret ion chamberA passive detector in which an electrostatically charged disc (electret) loses charge as radiation from radon ionizes the air inside a chamber. The measured voltage drop over the exposure period gives the average radon concentration.Continuous radon monitorAn electronic device that measures and records radon concentration over time, typically displaying hourly or daily values. Useful for observing variations, screening and checking mitigation systems, though laboratory-analysed long-term tests remain the standard for regulatory decisions.