A gaseous radioactive element, atomic no. 86, resulting from the breakdown of radium; of the isotopes with mass numbers between 198 and 228, only 222Rn is medically significant as an a-emitter, with a half-life of 3.8235 days; it is used in the treatment of certain malignancies. Poorly ventilated homes in some parts of the country have accumulated a dangerous amount of naturally occurring radon gas.
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Examples: glitazone, GI cocktail, etc.