Electromagnetic Transition Rates inNi58

Abstract

Lifetimes of 15 excited states in ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ and one in ${}_{}{}^{62}{}_{}{}^{}\mathrm{Ni}$ have been measured using the Doppler-shift-attenuation method. The levels were excited via inelastic proton scattering at bombarding energies from 7 to 9 MeV. The Doppler shifts of decay $\gamma$ rays were measured in a 30-${\mathrm{cm}}^3$ Ge(Li) detector in coincidence with particles backscattered near 170°. Theoretical estimates of stopping powers were checked experimentally by Dopplershift-attenuation measurements; excellent agreement was found. The matrix elements extracted from the measured lifetimes are compared with shell-model and vibrational-model predictions. Agreement is, in general, poor. The theoretical analysis indicates that a state-dependent neutron effective charge must be taken into account, and that core excitations play an important role in the determination of transition probabilities.