Two experiments have been performed using the ${}^{58}\mathrm{Ni}{(}^{32}\mathrm{S},3p)$ reaction at 135 MeV with Gammasphere and the Microball to study the high-spin structure of the transitional nucleus ${}^{87}\mathrm{Nb}.$ The first experiment using a thin target provided a considerable extension and refinement of the level scheme, as well as firm spin assignments from directional correlation of oriented nuclei. Sub-picosecond lifetimes were measured in the second backed-target experiment using the Doppler-shift attenuation method. The lifetimes imply a rather modest average deformation of ${\beta }_2\sim 0.1,$ but with considerable variation from state to state. Strong alternations were observed in the $B\left(M1\mathrm{}\right)\mathrm{}$ strengths of transitions between some pairs of bands. The experimental results were compared with calculations performed within the cranked Nilsson-Strutinsky approach. The calculations generally reproduce the irregularities in the structure of the yrast lines and plunging transition quadrupole moments $Q_t$ within the bands explaining them as reflections of configuration changes and an approach of band termination, respectively.

• Received 23 September 2002

DOI:https://doi.org/10.1103/PhysRevC.67.034316