What Is Radon?

The Definition of Radon

Radon is a gaseous radioactive element having the symbol Rn, the atomic number 86, an atomic weight of 222, a melting point of -71ºC, a boiling point of -62ºC, and (depending on the source, there are between 20 and 25 isotopes of radon – 20 cited in the chemical summary, 25 listed in the table of isotopes); it is an extremely toxic, colorless gas; it can be condensed to a transparent liquid and to an opaque, glowing solid; it is derived from the radioactive decay of radium and is used in cancer treatment, as a tracer in leak detection, and in radiography. (From the word radium, the substance from which it is derived.)

Sources: Condensed Chemical Dictionary, and Handbook of Chemistry and Physics, 69th ed., CRC Press, Boca Raton, FL, 1988.

See also:

• EPA’s Integrated Risk Information System profile on Radon 222 [CASRN 14859-67-7] is located at: epa.gov/iris/subst/0275.htm
• Conversion Factors for Radon Units
• Radon Decay Series Chart

Read more about Radon at www.epa.gov/radon