Authors
Little, D.; Ayangeakaa, A. D.; Janssens, R.; Zhu, S.; Tsunoda, Y.; Otsuka, T; Brown, B. A.; Carpenter, M. P.; Gade, A.; Rhodes, D.; Hoffman, C. R.; Kondev, F. G.; Lauritsen, T.; Seweryniak, D.
Abstract
The structure of 64Ni, the heaviest stable Ni isotope, has been investigated via high-statisticsmulti-step safe Coulomb excitation to search for shape coexistence, a phenomenon recently observedin neutron-rich 66Ni and 70Ni as well as in doubly-magic, N = 40, 68Ni. The study was motivated byrecent, state-of-the-art Monte Carlo shell-model calculations (MCSM), where a Hamiltonian witheffective interactions incorporating the monopole tensor force predicts the existence of the shapecoexistence, also in the lower-mass 62,64Ni isotopes. A rich set of transition and static E2 matrixelements for both yrast and near-yrast structures were extracted from the differential Coulombexcitation cross sections. From comparisons between the new results and MCSM as well as othershell-model calculations, a clearer picture of the structure of 64Ni emerges. Specifically, the low-spinstates are shown to be dominated by proton and neutron excitations mainly within the f p shell,with minimal contribution from the g9/2 shape-driving neutron orbital. The agreement betweenexperimental data and MCSM results indicates a small oblate deformation for the 0+2level, anda spherical shape for the 0+3state. In addition, the small upper limit determined for the B(E2)probability of a transition associated with the decay of the recently observed 3463-keV, 0+4stateagrees with its proposed assignment to a prolate shape, herewith providing first evidence for tripleshape coexistence in a stable Ni isotope.