actinium

ac·tin·i·um  (k-tn-m)

n. Symbol Ac¹

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 21.6 years. Atomic number 89; melting point 1,050°C; boiling point (estimated) 3,200°C; specific gravity (calculated) 10.07; valence 3. See Table at element.

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[From Greek akts, aktn-, ray (from its radioactivity).]

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actinium

Noun

Chem a radioactive element of the actinide series, occurring as a decay product of uranium Symbol: Ac[Greek aktis ray]

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actinium  (k-tn-m)

Symbol Ac

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. See Periodic Table.

Thesaurus

Noun

1.

actinium - a radioactive element of the actinide series; found in uranium ores Ac, atomic number 89 chemical element, element - any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter uranium ore - any ore from which uranium can be extracted