The ${}^{143}\mathrm{Tb}$ nucleus has been studied with the ${}^{92}\mathrm{Mo}$ (${}^{54}\mathrm{Fe},$ $3p\gamma$) reaction at 240-MeV incident energy, extending the systematics of odd-$A,$ $N=78\mathrm{}$ isotones to higher $Z.\mathrm{}$ For the yrast band, excited states up to a spin of ${59/2}^{-}$ have been observed. The first allowed backbend occurs at a rotational frequency of $ħ\omega =0.38\mathrm{}\mathrm{MeV}.$ Three- and five-quasiparticle structures were identified, similar to those seen in lower mass $N=78\mathrm{}$ isotones. Two of these structures have characteristics typical of mixed proton-neutron oblate configurations with one pair of aligned $h_{11/2}$ neutrons. In addition, two bands consisting of stretched $E2\mathrm{}$ transitions have been observed with no known analogous structures in neighboring nuclei. The results are discussed in terms of the cranking model.

• Received 21 December 1998

DOI:https://doi.org/10.1103/PhysRevC.60.054304