Radons

Radons, commonly referred to as radon gas, denotes the radioactive chemical element radon (symbol Rn, atomic number 86). It is a noble gas produced by the decay of uranium and thorium in rocks and soils. The name radon derives from radium emanation.

As an odorless, colorless, and chemically inert gas, radon is radioactive and can move through soils and into buildings. The principal natural isotope is radon-222, with a half-life of about 3.8 days. Other natural isotopes include radon-220 (thoron) with a half-life of about 55.6 seconds and radon-219 with a half-life of a few seconds. The short half-lives of the thoron and actinon isotopes limit their travel from the source, while radon-222 can migrate more widely.

Radon originates in the uranium-238 and thorium-232 decay chains. It can accumulate in occupied spaces, particularly basements and ground-floor rooms, as it emanates from surrounding soil and enters buildings via cracks and openings. Inhalation of radon decay products increases the risk of lung cancer; it is a major source of natural radiation exposure and is a leading cause of cancer after smoking in many regions. Regulations and recommended action levels for indoor radon vary by country.

Detection and measurement employ both short-term and long-term methods, such as charcoal canisters, alpha-track detectors, and continuous radon monitors. Mitigation strategies include sealing entry points, improving ventilation, and, in some buildings, sub-slab depressurization to lower indoor radon levels.

Radon was identified as an emanation from radium by Friedrich Ernst Dorn in 1900; the term derives from radium emanation. It plays a key role as a natural tracer in geology and hydrology and remains primarily a health and environmental concern.