The reaction ${}^{58}\mathrm{Ni}{(}^{28}\mathrm{Si},\alpha n\gamma )$ at 90 MeV of projectile energy has been used to populate the $T_z=\frac{1}{2}$ nucleus ${}^{81}\mathrm{Zr}.$ $\gamma$ rays have been detected with the GASP array, and charged particles with the ISIS Silicon ball. The charged particle information allowed unambiguous assignment of $\gamma$ rays to ${}^{81}\mathrm{Zr}.$ Two rotational band structures with both signatures have been observed. They are discussed by comparison with similar bands in the $N=41\mathrm{}$ isotones and in $T_z=\frac{1}{2}$ nuclei from the $A\approx 80$ region, and on the basis of the cranked shell model and interacting boson-fermion model calculations.

• Received 27 July 1999

DOI:https://doi.org/10.1103/PhysRevC.61.024310