Definition of actinium in English:



(also Ac)
  • 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.

    ‘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.’
    • ‘Francium was discovered in 1939 by the French physicist Marguerite Perey while she was analyzing the products formed during the radioactive decay of actinium.’
    • ‘A proposal was patented for a ceramic block pessary using radioactive elements such as thorium, actinium and even radium.’



/akˈtinēəm/ /ækˈtɪniəm/


Early 20th century from Greek aktis, aktin- ‘ray’+ -ium.