actinium

[ ak-tin-ee-uhm ]

noun

, Chemistry.

1. a radioactive silver-white metallic element that glows blue in the dark, resembling the rare earths in chemical behavior and valence. : Ac; : 89; : 227.

actinium

/ ækˈtɪnɪəm /

noun

1. a radioactive element of the actinide series, occurring as a decay product of uranium. It is used as an alpha-particle source and in neutron production. Symbol: Ac; atomic no: 89; half-life of most stable isotope, ²²⁷Ac: 21.6 years; relative density: 10.07; melting pt: 1051°C; boiling pt: 3200 ± 300°C

actinium

/ ăk-tĭn′ē-əm /

1. 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.
2. See Periodic Table

Word History and Origins

Origin of actinium¹

First recorded in 1900–05; actin- + -ium

Word History and Origins

Origin of actinium¹

C19: New Latin, from actino- + -ium

Example Sentences

Other theorists have predicted that hydrides such as calcium hydride or actinium hydride should superconduct at close to room temperature—and at a pressure considerably less than that needed for CSH.

From Science Magazine

But other heavy elements could, like actinium, which is a bit lighter with 89 protons and 89 electrons.

From New York Times

The substance in question, actinium-227, emits alpha and beta radiation, both of which are charged particles.

From Washington Post

NRC investigators determined that the powder was actinium-227, a radioactive isotope, according to a Jan. 31 letter summarizing the incident.

From Washington Post

Traditionalists maintain that these comprise scandium, yttrium, lanthanum and actinium; a growing number thinks that lutetium and lawrencium should replace the last two on the basis of electronic structures.

From Nature