Thermal-neutron capture byNi58,Ni59, andNi60

Abstract

We have studied the primary and secondary {gamma} rays (414 in {sup 59}Ni, 390 in {sup 60}Ni, and 240 in {sup 61}Ni) following thermal-neutron capture by the stable {sup 58}Ni, radioactive {sup 59}Ni, and stable {sup 60}Ni isotopes. Most of these {gamma} rays have been incorporated into the corresponding level schemes consisting of 65 levels in {sup 59}Ni, 88 levels in {sup 60}Ni, and 40 levels in {sup 61}Ni. The measured neutron separation energies (S{sub n} in keV) for {sup 59}Ni, {sup 60}Ni, and {sup 61}Ni are, respectively, 8999.28{+-}0.05, 11 387.73{+-}0.05, and 7820.11{+-}0.05. The measured thermal-neutron capture cross sections (in barns) for {sup 58}Ni, {sup 59}Ni, and {sup 60}Ni are, respectively, 4.13{+-}0.05, 73.7{+-}1.8, and 2.34{+-}0.05. In all three cases, primary electric-dipole (E1) transitions account for the bulk of the total capture cross section. We have calculated these E1 partial cross sections (in {sup 59}Ni and {sup 61}Ni) using direct-capture theory and models of compound-nuclear capture. The agreement between theory and experiment is good. The experimental level schemes have been compared with the results from a large-basis shell-model calculation. The agreement was also found to be quite good.