Role of the νg9/2 orbital in the development of collectivity in the A≈60 region: The case of Co 61

An extensive study of the level structure of Co61 has been performed following the complex Mg26(Ca48,2α4npγ)Co61 reaction at beam energies of 275, 290, and 320 MeV using Gammasphere and the Fragment Mass Analyzer (FMA). The low-spin structure is discussed within the framework of shell-model calculations using the GXPF1A effective interaction. Two quasirotational bands consisting of stretched-E2 transitions have been established up to spins I=41/2 and (43/2), and excitation energies of ∼17 and ∼20 MeV, respectively. These are interpreted as signature partners built on a neutron ν(g9/2)2 configuration coupled to a proton πp3/2 state, based on cranked shell model (CSM) calculations and comparisons with observations in neighboring nuclei. In addition, four ΔI=1 bands were populated to high spin, with the yrast dipole band interpreted as a possible candidate for the shears mechanism, a process seldom observed thus far in this mass region