Shell-model study of 56Ni, 58Ni, 54Fe and 56Fe

Shell-model calculations of 56Ni, 58Ni, 54Fe and 36Fe are presented. States are assumed to belong to configurations involving no excitation and two-particle excitations from the 1 f 7 2 shell. A limited number of core-excited states corresponding to four-particle excitations are also taken into account in the cases of 56Ni and 58Ni. The effective two-body interaction in the (1f, 2p) shell is deduced from a non-local potential which reproduces the nucleon-nucleon scattering data. Calculated energy spectra and transition rates are not in good agreement with experiment. This is certainly related to the truncation of the basis. Some improvements are obtained when single-particle energy spacings are allowed to vary.