Identification of excited states in ¹¹⁷Cs: Systematics of the v(h_11/2)² alignment: Systematics of the ν(h_11/2)² alignment

Excited states have been identified in the very neutron-deficient ¹¹⁷₅₅Cs₆₂ nucleus. High-spin spectroscopy has been performed using the Gammasphere array, and the assignment of gamma-ray transitions to ¹¹⁷Cs 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 π(h_11/2)[550]1/2^- band of ¹¹⁷Cs. Two additional bands have been observed and are tentatively assigned to be based on protons in the [404]9/2⁺ and [422]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 ν(h_11/2)² alignment in the π[550]1/2^- band and of the π(h_11/2)² alignment in the [422]3/2⁺ band. The frequencies of these alignments can be qualitatively explained only if a neutron-proton interaction is taken into account.