COMPETING SINGLE-PARTICLE AND COLLECTIVE STRUCTURES IN NB-86

The high-spin structure of odd-odd Nb-86 was studied with the early im plementation of GAMMASPHERE using 36 Compton-suppressed Ge detectors a nd the MICROBALL, a 95-element full-sphere charged-particle detector a rray. High-spin states were populated using the Ni-58(S-32,3pn) reacti on at 135 MeV with beams from the 88-Inch Cyclotron at Lawrence Berkel ey National Laboratory. A number of bands were observed up to spins as high as (31(-)). The yrast positive-parity band shares many character istics with the pi g(9/2) x nu g(9/2) bands in other odd-odd f-p-g she ll nuclei. These similarities include the behavior of the moments of i nertia,the magnitude and phase of the signature splitting and its phas e 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 nega tive-parity bands start out with a sharp upbend and then gradually fal l back to the rigid-body value. New positive- and negative-parity band s appear in the quasiparticle alignment region and eventually become y rast. Some additional positive-parity states around spin 17 (h) over b ar are candidates for fully or nearly fully aligned shell-model-like c onfigurations.