Radon

Radon is a chemical element with the symbol Rn and atomic number 86. It is a noble gas that is colorless, odorless, and tasteless, and it is radioactive. The most common isotope, radon-222, is produced by the alpha decay of radium-226, a member of the uranium-238 decay chain. Radon-222 has a half-life of about 3.8 days.

As a gas, radon is dense and can accumulate in enclosed spaces, particularly basements and lower levels, because it is heavier than air. It enters buildings from soil, rock, and building materials through cracks and openings. Indoor radon levels vary with geology, construction, and ventilation. Radon decays through short-lived progeny that readily attach to dust and aerosols; inhalation delivers alpha radiation to lung tissue.

Health effects associated with long-term exposure include an increased risk of lung cancer. Radon is the second leading cause of lung cancer after smoking, and risk rises with concentration and duration of exposure. The danger is greatest for smokers or former smokers, but non-smokers are also at risk.

Measurement and regulation: Radon concentration is expressed in becquerels per cubic meter (Bq/m^3) or picocuries per liter (pCi/L). In the United States, the Environmental Protection Agency recommends mitigation for homes at or above 4 pCi/L (about 148 Bq/m^3). The World Health Organization guideline is 100 Bq/m^3 or lower; national action levels vary by country.

Mitigation and testing: Radon testing, including short-term and long-term methods, is used to assess levels. Mitigation methods include sub-slab depressurization, sealing entry routes, improving crawlspace or foundation ventilation, and installing radon-resistant construction features in new buildings.

History: The gas was identified in 1900 by Friedrich Dorn as emanation from radium and was named radon, from radium emanation.