Low-lying excitations in Ni-72

Abstract

Low-lying excited states in Ni-72 have been investigated in an in-flight fission experiment at the RIBF facility of the RIKEN Nishina Center. The combination of the state-of-the-art BigRIPS and EURICA setups has allowed for a very accurate study of the beta decay from Co-72 to Ni-72, and has provided first experimental information on the decay sequence Fe-72 -> Co-72 -> Ni-72 and on the delayed neutron-emission branch Co-73 -> Ni-72. Accordingly, we report nearly 60 previously unobserved gamma transitions which deexcite 21 new levels in Ni-72. Evidence for the location of the so-sought-after (4(2)(+)), (6(2)(+)), and (8(1)(+)) seniority states is provided. As well, the existence of a low-spin beta-decaying isomer in odd-odd neutron-rich Co isotopes is confirmed for mass A = 72. The new experimental information is compared to simple shell-model calculations including only neutron excitations across the fpg shells. It is shown that, in general, the calculations reproduce well the observed states.