Actinium

3 definitions found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Actinium \Ac*tin"i*um\, n. [Gr. ?, ?, ray.] (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.
     [1913 Webster]



From WordNet (r) 2.0 [wn]:

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

From Elements database 20001107 [elements]:

  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.