ac·tin·i·um /ækˈtɪniəm/
 錒


 ac·tin·i·um /ækˈtɪnɪəm/ 名詞



 Ac·tin·i·um n.  Chem. A supposed metal, said by Phipson to be contained in commercial zinc; -- so called because certain of its compounds are darkened by exposure to light.

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 actinium
      n : a radioactive element of the actinide series; found in
          uranium ores [syn: Ac, atomic number 89]


 actinium
 Symbol: Ac
 Atomic number: 89
 Atomic weight: (227)
 Silvery radioactive metallic element, belongs to group 3 of the periodic
 table. The most stable isotope, Ac-227, has a half-life of 217 years.
 Ac-228 (half-life of 6.13 hours) also occurs in nature. There are 22 other
 artificial isotopes, all radioactive and having very short half-lives.
 Chemistry similar to lanthanum. Used as a source of alpha particles.
 Discovered by A. Debierne in 1899.