'actinium' definitions:
Definition of 'actinium'
(from WordNet)
noun
A radioactive element of the actinide series; found in uranium ores [syn: actinium, Ac, atomic number 89]
Definition of 'actinium'
From: Elements
- 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.