What is Radon?
Radon is a radioactive chemical element, which is colorless, odorless and tasteless in property. It occurs naturally as an intermediate step in the normal radioactive decay chains through which thorium and uranium slowly decay into lead. Radon, itself, is a decay product of radium. Radon will be present in nature long into the future in spite of its short half-life as it is continually being regenerated. About half of the total radiation effective dose to the general public is due to the irradiation of the lungs by alpha particles following the inhalation of radon decay products.
Radon gas is a health hazard. It is often the single largest contributor to an individual’s background radiation dose. Exposure to natural airborne radon in indoors has been identified as the primary mode of radiation exposure. Despite its short lifetime, radon gas from natural sources can accumulate in buildings, especially, due to its high density, in low areas such as basements and crawl spaces. Radon can also occur in ground water – for example, in some spring waters and hot springs.
It has been established that, the dose due to inhaled radon and its progeny accounts for more than 50% of the total radiation dose that the world population receive from the natural sources of radiation.  It has also been found that the radon and its progeny are responsible for 5-20% of all lung cancer deaths in USA and hence about 21,000 lung cancer deaths occur annually from radon-induced lung cancer in the USA. According to the United States Environmental Protection Agency, radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the United States. As radon itself decays, it produces other radioactive elements called radon daughters (also known as radon progeny) or decay products. Unlike the gaseous radon itself, radon daughters are solids and stick to surfaces, such as dust particles in the air. If such contaminated dust is inhaled, these particles can also cause lung cancer.