New high spin states and band termination in 83Y and 84Zr

The gamma decay of high spin yrast states in 83Y up to Iπ=59/2+ and 53/2- have been observed using the reaction 58Ni(29Si,3p) at 110 MeV and the Gammasphere Early Implementation Array. The level scheme has been substantially extended due to the observations of several new transitions in all of the bands. A sequence of transitions feeding into the positive parity yrast band above Iπ=47/2+ seems to be consistent with a noncollective oblate structure expected at these high spins. A similar cascade is found in the data for 84Zr. A new forking of the favored negative parity band is found which may be due to neutron alignment polarizing the core to a different shape. This suggests that the open-quotes isomeric close-quote close-quote band in 83Y, for which one more connecting transition was found, is of a similar nature to other high-K bands found in this region. Lifetime measurements in the unfavored negative parity band are consistent with cranking calculations which predict a nearly oblate shape with a deformation parameter β2∼0.2. A qualitative analysis of line shapes at very high spins suggests the persistence of collectivity in the yrast sequence to the highest excitations seen. copyright 1997 The American Physical Society