Title: Einsteinium
CAS Registry Number: 7429-92-7
Literature References: Es; at. no. 99; valence 3, 2. Man-made radioactive element. No stable nuclides; known isotopes (mass numbers): 243-256. Longest-lived known isotope: 252 (T½ 472 days, a-emitter, rel. at. mass 252.0830). 253Es (T½ 20.47 days, a-emitter) originally discovered in debris from a thermonuclear test explosion in Nov. 1952. Reviews of discovery: A. Ghiorso et al., Phys. Rev. 99, 1048-1049 (1955); A. Ghiorso, G. T. Seaborg, Sci. Am. 195 (6), 67-80 (1956). Prepn of isotopes: A. Chetham-Strode, Jr., L. W. Holm, Phys. Rev. 104, 1314 (1956); B. G. Harvey et al., ibid. 1315; G. T. Seaborg, J. Chem. Educ. 36, 38 (1959). Reviews: C. Keller, The Chemistry of the Transuranium Elements (Verlag Chemie, Weinheim, English Ed., 1971) pp 583-589, Silva, "Trans-Curium Elements" in MTP Int. Rev. Sci.: Inorg. Chem., Ser. One vol. 8, A. G. Maddock, Ed. (University Park Press, Baltimore, 1972) pp 71-105; Comprehensive Inorganic Chemistry vol. 5, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) passim; Handb. Exp. Pharmakol. 36, 689-928 (1973); E. K. Hulet in The Chemistry of the Actinide Elements vol. 2, J. J. Katz et al., Eds. (Chapman and Hall, New York, 1986) pp 1071-1085; The Elements Beyond Uranium, G. T. Seaborg, W. D. Loveland, Eds. (John Wiley & Sons, Inc., New York, 1990) pp 28-38.
Properties: Metal; two crystalline forms: double hexagonal close-packed a-form exists below 860°; face-centered cubic b-form, d 8.84. mp 860 ±50°.
Melting point: mp 860 ±50°
Density: d 8.84
CAUTION: Radiation hazard; handling requires special equipment and shielding facilities (Katz et al., loc. cit. vol. 2, p. 1128).

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