[W/K] :: radon

  Noble \No"ble\, a. [Compar. Nobler; superl. Noblest.] [F.
     noble, fr. L. nobilis that can be or is known, well known,
     famous, highborn, noble, fr. noscere to know. See know.]
     1. Possessing eminence, elevation, dignity, etc.; above
        whatever is low, mean, degrading, or dishonorable;
        magnanimous; as, a noble nature or action; a noble heart.
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              Statues, with winding ivy crowned, belong
              To nobler poets for a nobler song.    --Dryden.
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     2. Grand; stately; magnificent; splendid; as, a noble
        edifice.
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     3. Of exalted rank; of or pertaining to the nobility;
        distinguished from the masses by birth, station, or title;
        highborn; as, noble blood; a noble personage.
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     Note: Noble is used in the formation of self-explaining
           compounds; as, noble-born, noble-hearted, noble-minded.
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     Noble gas (Chem.), a gaseous element belonging to group
        VIII of the periodic table of elements, not combining with
        other elements under normal reaction conditions;
        specifically, helium, neon, argon, krypton,
        xenon, or radon; also called inert gas.
  
     Noble metals (Chem.), silver, gold, and platinum; -- so
        called from their resistance to oxidation by air and to
        dissolution by acids. Copper, mercury, aluminium,
        palladium, rhodium, iridium, and osmium are sometimes
        included.
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     Syn: Honorable; worthy; dignified; elevated; exalted;
          superior; sublime; great; eminent; illustrious;
          renowned; stately; splendid; magnificent; grand;
          magnanimous; generous; liberal; free.
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  Radon \Ra"don\ (r[=a]"d[o^]n), n. (Chem.)
     An intensely radioactive gaseous element produced by the
     radioactive decay of radium-226, which is the main isotope of
     radium found in pitchblende. Chemically it is an inert noble
     gas. Its atomic symbol is Rn. It has an atomic number of 86.
     The radon isotope produced by decay of radium has an atomic
     weight of 222.017, and this isotope decays by alpha emission
     with a half-life of 3.82 days. Numerous other isotopes have
     been observed, all radioactive and all having half-lives
     shorter than that of radon-222. Radon was discovered by M.
     and Mme. Curie, of Paris, in their studies of the radioactive
     substances in pitchblende. Radon was originally called
     radium emanation or exradio.
     [PJC]

  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.