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 (T 1/2 1.38 × 103 years, α-decay, rel. at. mass 247.0703). Prepn of first isotope, 243Bk (T 1/2 4.5 hrs, electron capture and α-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 (T 1/2 320 days, β-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.