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 $\ensuremath{\gamma}$ rays were measured in a 30-${\mathrm{cm}}^{3}$ Ge(Li) detector in coincidence with particles backscattered near 170\ifmmode^\circ\else\textdegree\fi{}. 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.