From the CRC handbook of Chemistry and Physics, CRC Press, Cleveland, 55th ed., 1974-75 "The Elements" by C.R. Hammond. page B-5
Actinium (Gr. aktis, aktinos, beam or ray), Ac; at. wt. (227); at. no. 89; m.p. 1050 C; b.p. 3200 C +/- 300 C (est.); sp. gr. 10.07 (calc.). Discovered by Andre Debierne in 1899 and independantly 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-yr 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 1100-1300 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-yr. half-life. It is about 150 times as active as radium, making it of value in the production of neutrons.
