radon (Rn) /rā″don/ [L, radiare, to emit rays] , a radioactive, chemically inert, gaseous element. Its atomic number is 86, and its atomic mass is 222. A decay product of radium, radon is used in radiation cancer therapy. Radon is also released by rocks, soil, and groundwater and is a common source of background radiation, with an intensity that varies in different geographic areas.
