CHAPTER ELEVEN CALIFORNIUM Richard

The discovery of californium came in the era of the syntheses and identifications of other transplutonium elements, following the end of World War II. The discovery of the element californium, like many of the other actinide elements, hinged on the development of new experimental techniques in conjunction with predictions based on nuclear systematics. Californium was named after the University and State of California where many of the transuranium elements were first identified. This element was discovered by Thompson, Street, Ghiorso, and Seaborg (Hyde et al., 1971; Seaborg and Loveland, 1990) in February, 1950. The discovery of californium came only 2 months after the preparation and identification of the first isotope of berkelium, element 97 (see Chapter 10). An account of the discovery and reminiscences about the early work on californium has been given by Ghiorso (1983). The first preparative method for californium was to bombard microgram targets of Cm with 35 MeV helium ions in a 60 in. cyclotron. This produced Cf by a (a,2n), reaction which decayed primarily by alpha emission (t1/2 1⁄4 19.4 min, with two different alpha energies having a 75% and 25% branching ratios; see Table 11.1). This isotope also has a small decay branch that proceeds via electron capture. Since element 98 (‘eka‐dysprosium’) was expected to have a stable tripositive oxidation state in aqueous solution, its elution behavior in chromatographic separation schemes was predicted and this was used as a guide to estimate which collection fractions should be examined for the new element. In addition to acquire a high degree of decontamination 11.