actinium

[ ak-tin-ee-uhm ]

nounChemistry.

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

Origin of actinium

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

Words Nearby actinium

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use actinium in a sentence

On Rutherford's theory then, actinium should always accompany uranium and radium, but in very subordinate amount.
The Birth-Time of the World and Other Scientific Essays | J. (John) Joly
For if actinium was an independent element we would be sure to find actinium haloes.
The Birth-Time of the World and Other Scientific Essays | J. (John) Joly
The element has since been found in nature as a small constituent of the natural decay of actinium.
A Brief History of Element Discovery, Synthesis, and Analysis | Glen W. Watson
The emanation deposits two successive disintegration products actinium-A and actinium-B.
Darwin and Modern Science | A.C. Seward and Others
What is the final non-active product of the series of changes we have traced from uranium through actinium and radium?
Darwin and Modern Science | A.C. Seward and Others

British Dictionary definitions for actinium

actinium

/ (ækˈtɪnɪəm) /

noun

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

Origin of actinium

C19: New Latin, from actino- + -ium

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for actinium

actinium

[ ăk-tĭn′ē-əm ]

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.

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