Several collective structures have been populated in the Z=55 nucleus ${}_{}{}^{123}{}_{}{}^{}\mathrm{Cs}$ following the ${}_{}{}^{108}{}_{}{}^{}\mathrm{Pd}$${(}^{19}$F,4n) fusion-evaporation reaction at a beam energy of 76 MeV. The low-lying structure is found to be dominated by a decoupled rotational band built on the unique-parity π${\mathit{h}}_{11/2}$ orbital. Rotational structures based on the normal-parity ${\mathit{g}}_{7/2}$ proton and the ${\mathit{g}}_{9/2}$ proton-hole orbitals are also observed. Rotational alignments occur in the π${\mathit{h}}_{11/2}$ band at ħ${\mathrm{\omega }}_{\mathit{c}}$≊0.44 MeV, and in the π${\mathit{g}}_{9/2}^{\mathrm{-}1}$ band at ħ${\mathrm{\omega }}_{\mathit{c}}$=0.38 MeV, both attributed to the rotational alignment of a pair of ${\mathit{h}}_{11/2}$ neutrons, despite the different crossing frequency. In addition, the γ-vibrational band built on the π${\mathit{h}}_{11/2}$ orbital has been observed feeding both signatures of the corresponding rotational cascade. These results are compared to cranked shell model calculations and to the systematics of the region.

• Received 5 December 1991

DOI:https://doi.org/10.1103/PhysRevC.45.2177