Proton inelastic scattering of ${}^{72,74}\mathrm{Ni}$ and ${}^{76,80}\mathrm{Zn}$ ions at energies around 235 MeV/nucleon was performed at the Radioactive Isotope Beam Factory and studied using $\gamma$-ray spectroscopy. Angular integrated cross sections for direct inelastic scattering to the $2_1^{+}$ and $4_1^{+}$ states were measured. The Jeukenne-Lejeune-Mahaux folding model, extended beyond 200 MeV, was used together with neutron and proton densities stemming from quasiparticle random-phase approximation (QRPA) calculations to interpret the experimental cross sections and to infer neutron to proton matrix element ratios. In addition, coupled-channels calculations with a phenomenological potential were used to determine deformation lengths. For the Ni isotopes, correlations favor neutron excitations, thus conserving the $Z=28$ gap. A dominance of proton excitation, on the other hand, is observed in the Zn isotopes, pointing to the conservation of the $N=50$ gap approaching ${}^{78}\mathrm{Ni}$. These results are in agreement with QRPA and large-scale shell-model calculations.

• Received 23 May 2017
• Revised 17 November 2017

DOI:https://doi.org/10.1103/PhysRevC.97.044315