α-decay of the new isotope Po187: Probing prolate structures beyond the neutron mid-shell at N = 104

The new neutron-deficient isotope Po187 has been identified in the complete fusion reaction Ti46+Sm144→Po187+3n at the velocity filter SHIP. Striking features of the Po187 α decay are the strongly-hindered decay to the spherical ground state and unhindered decay to a surprisingly low-lying deformed excited state at 286 keV in the daughter nucleus Pb183. Based on the potential energy surface calculations, the Po187 ground state and the 286 keV excited state in Pb183 were interpreted as being of prolate origin. The systematic deviation of the α-decay properties in the lightest odd-A Po isotopes relative to the smooth behavior in the even-A neighbors is discussed. Improved data for the decay of 187Bim,g were also obtained. © 2006 The American Physical Society.