actinium

American  

[ak-tin-ee-uhm] / ækˈtɪn i əm /

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.

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actinium British  

/ 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, ²²⁷ Ac: 21.6 years; relative density: 10.07; melting pt: 1051°C; boiling pt: 3200 ± 300°C

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actinium Scientific  

/ 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

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Etymology

Origin of actinium

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

Example Sentences

Actinium, Ac, is the first member of the fourth transition series, which also includes Rf through Rg.

From Textbooks • Feb. 14, 2019

Actinium, an element or elementary substance obtained in minute quantities in connection with the study of radioactivity.

From The New Gresham Encyclopedia. Vol. 1 Part 1 A to Amide by Various

Actinium, one of the radioactive substances, is said to have a chemical activity which is about a thousand million times swifter than that of radium.

From What and Where is God? A Human Answer to the Deep Religious Cry of the Modern Soul by Swain, Richard la Rue

To that which accompanied barium taken from the same ore they called Radium and to the substance which was found among the rare earths of the pitchblende Debierne gave the name Actinium.

From Marvels of Modern Science by Severing, Paul