The role of the g9/2 orbital in the development of collectivity in the A = 60 region: The case of 61Co

TL;DR

This study investigates the nuclear structure of 61Co, revealing quasi-rotational bands and a potential shears mechanism, highlighting the role of the g9/2 orbital in nuclear collectivity around A=60.

Contribution

It provides new experimental data on high-spin structures and identifies a candidate for the shears mechanism in 61Co, supported by shell-model and Cranked Shell Model calculations.

Findings

Identification of two quasi-rotational bands up to high spins.

Observation of a possible shears mechanism in 61Co.

Confirmation of the role of the g9/2 orbital in nuclear collectivity.

Abstract

An extensive study of the level structure of 61Co has been performed following the complex 26Mg(48Ca, 2a4npg)61Co 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 quasi-rotational 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 {\nu}(g9/2)2 configuration coupled to a proton {\pi}p3/2 state, based on Cranked Shell Model (CSM) calculations and comparisons with observations in neighboring nuclei. In addition, four I = 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.