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ACTINIUM
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Atomic Number:

89

Atomic Symbol:

Ac

Atomic Weight:

227

Electron Configuration:[Rn]7s26d1
Total Isotopes39
Total Isomers8
Radioactive Isotopes31
Stable Isotopes0
X-Ray Energies
90.88
102.9
LL10.87
12.65
Mz2.30
2.92

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History

(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: Los Alamos National Laboratory; CRC Handbook of Chemistry and Physics; American Chemical Society
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