High-spin spectroscopy near the deformed N ≈ Z ≈ 38 shell gap: The light Rb isotopes

Abstract

Nuclei near the prolate single-particle energy gap at proton number Z = 38 ( ε 2 ≈ +0.38) and neutron number N ≈ Z offer unique possibilities to study the pn-interaction at large quadrupole deformation. In the yrast band of the Z = N = 37 nucleus 74Rb, we have identified a crossing of the T = 1 pn-paired band (even spins) with the T = 0 pn-unpaired band (odd spins). In 77Rb, the positive-parity yrast and yrare bands have been followed over large spin ranges and assigned different 1qp-proton 2qp-neutron structures. These band crossings do not follow the usual pattern of two identical particles aligning in high-j orbits. In addition, an aligned g 9 2 proton-neutron negative-parity sequence with K= 11 2 has been identified in 77Rb Rotational bands with more conventional band crossings have also been found.