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

A radioactive, metallic chemical element (symbol: Ac) with an atomic number of 89; found in uranium ores.

Wiktionary
Synonyms:
  • atomic number 89
  • ac
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other
A silvery-white, highly radioactive metallic element of the actinide series that is found in uranium ores. It is about 150 times more radioactive than radium and is used as a source of alpha rays and neutrons. Its most stable isotope has a half-life of about 22 years. Atomic number 89; melting point 1,050°C (1,922°F); boiling point (estimated) 3,200°C (5,792°F); specific gravity (calculated) 10.07; valence 3.
American Heritage Science
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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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