New band structures and an unpaired crossing in Kr-78

High-spin states in Kr-78 were studied using the Ni-58(Na-23,3p) reaction a t 70 MeV and the Ni-58(Si-23,alpha 4p) reaction at 130 MeV. Prompt gamma-ga mma coincidences were measured using the Pitt-FSU detector array and the GA MMASPHERE-MICROBALL array. Results from these experiments have led to 26 ne w excitation levels, some of which have been grouped into 3 new bands. Spin s were assigned based on directional correlations of oriented nuclei. Two o f the new negative-parity bands appear to form a signature-partner pair bas ed on a two-quasineutron structure, in contrast to the previously known two -quasiproton negative-parity bands. A forking has been observed at the 24() state in the yrast band, which calculations suggest may result from an un paired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands. [S0556-2813 (99)04602-6].