Definition of actinium in English:

actinium

Syllabification: ac·tin·i·um
Pronunciation: /akˈtinēəm
 
/

noun

The chemical element of atomic number 89, a radioactive metallic element of the actinide series. It is rare in nature, occurring as an impurity in uranium ores. (Symbol: Ac)
More example sentences
  • Along the way, these disintegration series produce radioactive isotopes of protactinium, thorium, actinium, radium, francium, radon, astatine, polonium, bismuth, lead, thallium and mercury.
  • Actinides - the radioactive chemical elements that span from actinium to lawrencium on the periodic table - have generated a great deal of interest in recent years.
  • The first four actinide elements, actinium, thorium, protactinium and uranium are naturally occurring and have been known for a considerable time.

Origin

early 20th century: from Greek aktis, aktin- 'ray' + -ium.

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