No abstract

The ␣ decay of 188,192 Po has been reexamined in order to probe the 0 + states in the daughter nuclei 184,188 Pb that can be associated with coexisting spherical, oblate, and/or prolate configurations. Improved values were measured for the excitation energy and the feeding ␣-decay intensity of the 0 2 + state in 184,188 Pb and conflicting results on the 0 3 + state in 188 Pb were clarified. All known cases of fine structure in the ␣ decay of the even-even Po nuclei are reviewed. The reduced ␣-decay width systematics combined with potential-energy-surface calculations confirm the onset of deformation in the ground state of the polonium nuclei around the neutron midshell. An isomeric state with a half-life of 580͑100͒ns has been identified in 192 Po.

Proton and ␣ decay of the proton-rich nuclide 185 Bi has been restudied in more detail in the complete fusion reaction 93 Nb͑ 95 Mo, 3n͒ 185 Bi at the velocity filter SHIP. The observed decay pattern of 185 Bi and of the heavier odd-mass isotopes 187,189,191,193 Bi are interpreted based on potential-energy surface calculations. It is shown that the experimental systematics of the particle decays and of the excited states in these nuclei (where known) can be explained by the prolate-oblate shape co-existence at low excitation energy. The observed state in 185 Bi is proposed to be of prolate nature, which is in contrast with the previously proposed oblate interpretation.