 3 definitions found
From WordNet (r) 2.0 [wn]:
actinium
noun: a radioactive element of the actinide series; found in
uranium ores [syn: {Ac}, {atomic number 89}]
From The Collaborative International Dictionary of English v.0.44 [gcide]:
Actinium \Ac*tin"i*um\, noun [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.
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.
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