- A radioactive element formed as a gas during the breakdown of radium.
* * *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 alpha-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 accumulate a dangerous amount of naturally occurring r. gas. [from radium]
* * *ra·don 'rā-dän n a heavy radioactive gaseous element of the group of inert gases formed by disintegration of radium and used similarly to radium in medicine symbol Rn called also radium emanation see ELEMENT (table)
* * *n.a radioactive gaseous element that is produced during the decay of radium. Sealed in small capsules called radon seeds, it is used in radiotherapy for the treatment of cancer, but has largely been replaced by newer agents and techniques. It emits alpha and gamma radiation. Symbol: Rn.
* * *ra·don (Rn) (raґdon) a heavy, colorless, gaseous, radioactive element; atomic weight, 222; atomic number, 86; obtained by the breaking up of radium, and used in radiotherapy. 219Rn is a radioactive isotope of the actinium radioactive series. 220Rn is a radioactive isotope of the thorium radioactive series.
Medical dictionary. 2011.