α Particles as Probes of Nuclear Shape in the Rare Earths and Structure Effects on Proton Emission in the Mass-80 Region

Low-emission barriers and large subbarrier anisotropies in the α-particle decay, with respect to the spin direction, of Sn and rare-earth compound nuclei are examined in the light of recent calculations incorporating deformation. For the rare-earth systems deformation which increases with spin is necessary to explain the data. Energy spectra and angular correlations of evaporated protons from the 52Cr(34S, 2p2n)82Sr reaction were measured in coincidence with discrete transitions. Large changes in the shape of the proton spectra were observed when high-spin states in different rotational bands are populated. These effects cannot be explained by phase space arguments that do not include explicitly structure in the deexcitation process. They are interpreted as resulting from near-yrast to near-yrast stretched proton emission, which preferentially populates the yrast band by subbarrier protons.