Title: Actinium
CAS Registry Number: 7440-34-8
Literature References: Ac; at. no. 89; valence 3. Group IIIB (3). No stable nuclides; known isotopes (mass numbers): 209-233; naturally occurring isotopes: 227, 228. Longest- lived isotope: 227Ac (T½ 21.773 ±0.003 years, mode of decay a, b, g-emission, rel. at. mass 227.0277). Daughter of 231Pa; parent of 227Th (radioactinium) and 223Fr. Originally extracted from uranium ores where it occurs naturally as a member of the 235U decay series; now prepd by neutron bombardment of 226Ra in nuclear reactors. 228Ac or mesothorium II (MsTh2) occurs naturally as a member of the 232Th decay series. T½ 6.13 ±0.03 hrs; decays by b and g-emission. Daughter of 228Ra (mesothorium I); parent of 228Th (radiothorium). Discovery of 227Ac: A. Debierne, C.R. Hebd. Seances Acad. Sci. 129, 593 (1899); F. O. Geisel, Ber. 55, 3608 (1902). Prepn of metal: J. G. Stites, Jr., et al., J. Am. Chem. Soc. 77, 237 (1955); J. D. Farr et al., J. Inorg. Nucl. Chem. 18, 42 (1961). Discovery of 228Ac: O. Hahn, Ber. 40, 1462 (1907). Review of actinium and the actinides: Comprehensive Inorganic Chemistry vol. 5, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) passim; H. W. Kirby in The Chemistry of the Actinide Elements vol. 1, J. J. Katz et al., Eds. (Chapman and Hall, New York, 1986) pp 14-40; G. T. Seaborg in Kirk-Othmer Encyclopedia of Chemical Technology vol. 1 (Wiley-Interscience, New York, 4th ed., 1991) pp 412-444.
Properties: Cubic crystal, d25 10.07. mp 1050 ±50°. bp ~3300°. Homologous with lanthanum; more basic than lanthanum. Strong electropositive element. Forms insol salts, e.g. carbonate, oxalate, phopshate etc. just as the lanthanides. Rapidly oxidizes to AcO3 in moist air.
Melting point: mp 1050 ±50°
Boiling point: bp ~3300°
Density: d25 10.07
CAUTION: Radiation hazard; handling requires special equipment and shielding facilities (Katz et al., loc. cit. vol. 2, p 1128).

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