Identification of excited states in 117 Cs : Systematics of the ν ( h 1 1 / 2 ) 2 alignment

Excited states have been identified in the very neutron-deficient {sub 55}{sup 117}Cs{sub 62} nucleus. High-spin spectroscopy has been performed using the Gammasphere array, and the assignment of gamma-ray transitions to {sup 117}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{sub 11/2})[550]1/2{sup -} band of {sup 117}Cs. Two additional bands have been observed and are tentatively assigned to be based on protons in the [404]9/2{sup +} and [422]3/2{sup +} orbitals. Alignments of pairs of h{sub 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{sub 11/2}){sup 2} alignment in the {pi}[550]1/2{sup -} band and of the {pi}(h{sub 11/2}){sup 2} alignment in the [422]3/2{sup +} band. The frequencies of these alignments can be qualitatively explained only if a neutron-proton interaction is taken into account.