Effective interactions and charges in ⁵⁸Ni

Abstract

The structure of the low-lying states of ⁵⁸Ni has been calculated in shell model by assuming an inert ⁵⁶Ni core plus two valence nucleons in the p_3/2, f_5/2 and p_1/2 orbitals. The two-body matrix elements are first expressed in terms of seven radial matrix elements and these are then parametrized to give best fit between the computed and the observed energies of the levels below 4 MeV. The wave-functions obtained using these two-body matrix elements are used to study the concept of effective charges. It is found that a single effective charge is not sufficient to predict the B(E2) rates equally well for the thirteen known transitions for which experimental values are available. Assumption of state-dependent effective charges gives a far better agreement. An analysis using wave functions obtained with Kuo's two-body matrix elements also gives a similar result.