Title: Berkelium
CAS Registry Number: 7440-40-6
Literature References: Bk; at. no. 97; valence 3, 4. Man-made radioactive element; second element in the curide series. No stable nuclides, known isotopes (mass numbers): 240, 242-251. Longest-lived known isotope: 247 (T½ 1.38 ´ 103 years, a-decay, rel. at. mass 247.0703). Prepn of first isotope, 243Bk (T½ 4.5 hrs, electron capture and a-decay) by helium ion bombardment of 241Am: S. G. Thompson et al., Phys. Rev. 77, 838 (1950); eidem, ibid. 80, 781. Prepn of macroscopic quantities as 249Bk (T½ 320 days, b-decay, rel. at. mass 249.0750): B. B. Cunningham, J. Chem. Educ. 36, 32-37 (1959). Prepn of metal and determn of crystal structure: J. A. Fahey, U.S. Atomic Energy Commission TID-25741 (1971) 119 pp, C.A. 76, 9882r (1972); J. R. Peterson et al., J. Inorg. Nucl. Chem. 33, 3345 (1971). Reviews: M. Haissinsky, J.-P. Adloff, Radiochemical Survey of the Elements (Elsevier, New York, 1965) pp 14-15; C. Keller, The Chemistry of the Transuranium Elements (Verlag Chemie, Weinheim, English Ed., 1971) pp 553-566; 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); D. E. Hobart, J. R. Peterson in The Chemistry of the Actinide Elements vol. 1, J. J. Katz et al., Eds. (Chapman and Hall, New York, 1986) pp 989-1024.
Properties: Metal. Two allotropic forms: double hexagonal close-packed a-form, d (calc) 14.78, transforms to b-form at 930°; face-centered cubic b-form, d (calc) 13.25, exists from 930-986°. mp 986 ± 25° (Fahey). Also reported as mp 1050° (Katz et al., loc. cit. vol. 2, p 1150). Changes from the trivalent to the tetravalent state under the influence of oxidizing agents. In the trivalent state, its chemical properties are very close to those of curium. Can be separated from other transuranium elements by ion-exchange or by extraction of Bk(IV) with dioctylphosphoric acid in heptane (Haissinsky, Adloff). Metal dissolves rapidly in aqueous mineral acids.
Melting point: mp 986 ± 25° (Fahey); mp 1050° (Katz et al., loc. cit. vol. 2, p 1150)
Density: d (calc) 14.78; d (calc) 13.25
CAUTION: Radiation hazard; handling requires special equipment and shielding facilities (Katz et al., loc. cit. vol. 2, p 1128).

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