Units
Working Level (WL)
A historical unit for the concentration of radon decay products in air, originally defined for uranium mines. Cumulative occupational exposure is measured in Working Level Months (WLM), a quantity still used in epidemiological studies of miners.
Related terms
Becquerel (Bq)The SI unit of radioactivity: one becquerel equals one radioactive disintegration per second. Radon in air is expressed as an activity concentration, in becquerels per cubic metre (Bq/m³).Becquerels per cubic metre (Bq/m³)The standard unit for radon concentration in air in Europe and in WHO guidance: the number of radon disintegrations per second in each cubic metre of air. Reference levels are typically 100–300 Bq/m³. 1 pCi/L = 37 Bq/m³.Picocuries per litre (pCi/L)The traditional unit for radon concentration used in the United States. One picocurie per litre equals 37 becquerels per cubic metre; the US EPA action level of 4 pCi/L therefore corresponds to about 148 Bq/m³.Sievert (Sv)The SI unit of effective radiation dose, which weights the absorbed energy by radiation type and tissue sensitivity. Radon exposure is often converted to millisieverts per year (mSv/y) to compare it with other radiation sources; in many countries radon is the largest natural contributor to the population dose.