Excited states have been identified in the very neutron-deficient ${}_{55}^{117}{\mathrm{Cs}}_{62}$ nucleus. High-spin spectroscopy has been performed using the Gammasphere array, and the assignment of gamma-ray transitions to ${}^{117}\mathrm{Cs}$ has been made in a separate experiment in which gamma rays were detected in coincidence with x rays and with recoiling evaporation residues. A previously observed sequence of five gamma rays has been extended by 11 transitions, to high spin, and has been identified as the yrast $\pi {(h}_{11/2}\left)\right[550]{1/2}^{-}$ band of ${}^{117}\mathrm{Cs}.$ Two additional bands have been observed and are tentatively assigned to be based on protons in the $\left[404\right]{9/2}^{+}$ and $\left[422\right]{3/2}^{+}$ orbitals. Alignments of pairs of $h_{11/2}$ neutrons and protons are observed in all of the bands. The alignments are compared to cranked Woods-Saxon calculations, and are discussed with respect to the effects of a neutron-proton interaction. Of particular interest are the features of the $\nu {(h}_{11/2}{)}^2$ alignment in the $\pi \left[550\right]{1/2}^{-}$ band and of the $\pi {(h}_{11/2}{)}^2$ alignment in the $\left[422\right]{3/2}^{+}$ band. The frequencies of these alignments can be qualitatively explained only if a neutron-proton interaction is taken into account.

• Received 16 September 2000

DOI:https://doi.org/10.1103/PhysRevC.63.024319