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 πg_9/2⊗νg_9/2 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 17ħ are candidates for fully or nearly fully aligned shell-model-like configurations.