Competing single-particle and collective structures in 86Nb

The high-spin structure of odd-odd 86Nb was studied with the early implementation of GAMMASPHERE using 36 Compton-suppressed Ge detectors and the MICROBALL, a 95-element full-sphere charged-particle detector array. High-spin states were populated using the 58Ni(32S,3pn) reaction at 135 MeV with beams from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. A number of bands were observed up to spins as high as (31-). The yrast positive-parity band shares many characteristics with the πg9/2 circle-times νg9/2 bands in other odd-odd f-p-g shell nuclei. These similarities include the behavior of the moments of inertia, the magnitude and phase of the signature splitting and its phase reversal near the 10+ state, and the strong alternations in the B(M1)/B(E2) strengths. The moments of inertia in the lowest pair of negative-parity bands start out with a sharp upbend and then gradually fall back to the rigid-body value. New positive- and negative-parity bands appear in the quasiparticle alignment region and eventually become yrast. Some additional positive-parity states around spin 17ℎ are candidates for fully or nearly fully aligned shell-model-like configurations. copyright 1997 The American Physical Society