Actinium Definition
ăk-tĭnē-əm
noun
A radioactive element found in uranium ores, used in equilibrium with its decay products as a source of alpha rays. Its longest lived isotope is Ac-227 with a half-life of 21.77 years. Atomic number 89; melting point 1,050°C; boiling point 3,198°C; specific gravity (calculated) 10.07; valence 3.
American Heritage
A white, radioactive, metallic chemical element, the first member of the actinide series, found in pitchblende and other minerals or formed in reactors by the neutron irradiation of radium: symbol, Ac; at. no. 89
Webster's New World
Synonyms:
- atomic number 89
- ac
Origin of Actinium
-
From Greek aktīs aktīn- ray (from its radioactivity) nekw-t- in Indo-European roots
From American Heritage Dictionary of the English Language, 5th Edition
actin- + -ium
From Wiktionary
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