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 ra·don /ˈreˌdɑn/
 氡

 ra·don /ˈredɑn/ 名詞
 氡

 radon
      n : a radioactive gaseous element formed by the disintegration
          of radium; the heaviest of the inert gasses; occurs
          naturally (especially in areas over granite) and is
          considered a hazard to health [syn: Rn, atomic number
          86]

 radon
 Symbol: Rn
 Atomic number: 86
 Atomic weight: (222)
 Colorless radioactive gaseous element, belongs to the noble gases. Of the
 twenty known isotopes, the most stable is Rn-222 with a half-life of 3.8 days.
 Formed by the radioactive decay of Radium-226. Radon itself decays into
 polonium. Used in radiotherapy. As a noble gas, it is effectively inert,
 though radon fluoride has been synthesized. First isolated in 1908 by Ramsey
 and Gray.