Title: Americium
CAS Registry Number: 7440-35-9
Literature References: Am; at. no. 95; valences 3, 4, 5, 6. Man-made radioactive element. No stable nuclides; known isotopes (mass numbers): 234, 237-247. Longest-lived known isotope 243 (T½ 7.38 ´ 103 years, rel. at. mass 243.0614, a-emitter). First isotope prepared: 241Am (T½ 432.7 years, a and g-emitter, rel. at. mass 241.0568); prepd in 1944 by G. T. Seaborg et al. in The Transuranium Elements, G.T. Seaborg et al., Eds., (McGraw-Hill, New York, 1949) p 1525-1553; eidem, Phys. Rev. 78, 472 (1950). Isoln: Armstrong et al., A. I. Ch. E. J. 3, 286 (1957); Coleman, J. Inorg. Nucl. Chem. 3, 327 (1957). Prepn of metal: E. F. Westrum, Jr., L. Eyring, J. Am. Chem. Soc. 73, 3396 (1951); Cunningham, Lohr, ibid. 2026. Superconducting properties: J. L. Smith, R. G. Haire, Science 200, 535 (1978). Clinical application in bone mineral determn: E. G. De Puey et al., J. Nucl. Med. 16, 891 (1975); in cancer radiotherapy: R. Nath et al., Int. J. Radiat. Oncol. Biol. Phys. 14, 969 (1988). Reviews: C. Keller, The Chemistry of the Transuranium Elements (Verlag Chemie, Weinheim, English Ed., 1971) pp 485-527; Comprehensive Inorganic Chemistry vol. 5, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) passim; Handb. Exp. Pharmakol. 36, 689-940 (1973); W. W. Schulz, R. A. Penneman in The Chemistry of the Actinide Elements vol. 2, J. J. Katz et al., Eds. (Chapman and Hall, New York, 1986) pp 887-961. See also metabolism study of internal contamination of 241Am in man: N. Cohen et al., Science 206, 64 (1979). Review of toxicology and human exposure: Toxicological Profile for Americium (PB2004-104396, 2004) 333 pp.
Properties: Silvery, ductile, very maleable, non-magnetic metal. Allotropic forms: double hexagonal close-packed a-form transforms to b-form at 658°; face-centered cubic b-form exists from 793-1004°; g-form exists from ~1050° to mp. mp 1173°. bp (calc) 2067°. d 13.671. Dissolves readily in aq HCl; insol in liquid NH3.
Melting point: mp 1173°
Boiling point: bp (calc) 2067°
Density: d 13.671
Derivative Type: Trivalent americium
Properties: The most common in aq soln. Color light pink changing to yellow with increasing concn. Sharp absorption peak at 5027 Å. Americium dioxide, AmO2, is obtained by ignition of most trivalent Am compounds.
Derivative Type: Tetravalent americium
Properties: Known only in the solid state. When AmO2 or AmF3 is treated with fluoride, solid AmF4 results.
Derivative Type: Pentavalent and hexavalent americium compds
Properties: When obtained in soln are doubly oxygenated and have the general formula AmO2+n, where n = +1 for Am(V) and n = +2 for Am(VI). Hexavalent americium is yellow or light brown in dilute perchloric or nitric acid, green in fluoride solns and dark brown in sulfuric acid. A deep red ion complex is formed in bicarbonate-carbonate solns.
CAUTION: Radiation hazard; handling requires special equipment and shielding facilities (Katz et al., loc. cit. vol. 2, p 1128).
Use: 241Am as radiation source for thickness gauging, density and radiographic measurements; parent for production of 242Cf and 242Pu; in ionization smoke detectors; for dissipation of static electrical charges. 241Am-Be mixture as neutron source. 243Am as target material for production of transcurium elements in high neutron-flux reactors.
Therap-Cat: 241Am as diagnostic aid (bone mineral analyzer); as antineoplastic (radiation source).

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