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actinium Line breaks: ac¦tin|ium
Pronunciation: /akˈtɪnɪəm/

Definition of actinium in English:


[mass 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)
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.


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

Words that rhyme with actinium

aluminium, condominium, delphinium
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