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(Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and
independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals.
Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year
half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223
(11.4-day half-life), and a number of short-lived products including radon, bismuth,
polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful
source of alpha rays. Actinium metal has been prepared by the reduction of actinium
fluoride with lithium vapor at about 1100 to 1300-degrees C. The chemical behavior of
actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium
comes into equilibrium with its decay products at the end of 185 days, and then decays
according to its 21.6-year half-life. It is about 150 times as active as radium, making it
of value in the production of neutrons.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.
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