Actinium

(Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 andindependently 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-yearhalf-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 powerfulsource of alpha rays. Actinium metal has been prepared by the reduction of actiniumfluoride with lithium vapor at about 1100 to 1300-degrees C. The chemical behavior ofactinium is similar to that of the rare earths, particularly lanthanum. Purified actiniumcomes into equilibrium with its decay products at the end of 185 days, and then decaysaccording to its 21.6-year half-life. It is about 150 times as active as radium, making itof value in the production of neutrons.