Radon-222 () is a naturally occurring radioactive noble gas produced by the decay of Radium-226 in the Uranium Decay Series. It is colorless, odorless, and tasteless, making it impossible to detect without specialized equipment. With a half-life of 3.82 days, it is the most stable isotope of radon.
As a noble gas, Radon-222 is chemically inert and highly mobile. It can diffuse through soil and rock pores, eventually escaping into the atmosphere or infiltrating buildings through cracks in foundations. In the oil and gas industry, radon can travel with the gas stream and accumulate in processing equipment, where its progeny form radioactive films on internal surfaces.
The primary radiological risk associated with Radon-222 comes not from the gas itself, but from its short-lived decay products, known as "radon daughters" or "progeny." These include isotopes of polonium, lead, and bismuth (e.g., Po-218, Pb-214, Bi-214). Unlike the parent gas, these progeny are solids that can attach to dust particles or the lining of the lungs.
Radon-222 is the second leading cause of lung cancer globally, after tobacco smoking. When inhaled, the short-lived progeny trapped in the lungs emit high-energy alpha particles. These particles can damage the DNA of bronchial epithelial cells, leading to mutations and eventually cancer. Managing this risk involves ensuring adequate ventilation and monitoring of Radon concentrations in both residential and industrial environments.
Radon gas is a significant component of NORM hazards. In mining and mineral processing, particularly with materials like Monazite, Radon-220 (Thoron) and Radon-222 can reach high concentrations. Because it can travel long distances from its source, Radon serves as a primary pathway for public exposure to terrestrial radioactivity.