Effect of oblate deformation on E3 strengths in light lead and polonium isotopes - art. no. 061302

The multipolarities of the main transitions deexciting yrast isomers in Pb- 190 have been measured using conversion electron spectroscopy with pulsed b eams. The enhanced E3 character of the 407 keV transition from the 11(-) is omer is confirmed and an independent value obtained for its lifetime. A new measurement of the properties of the 440 keV E3 decay from the correspondi ng 11(-) state in Pb-192, has resulted in the identification of a new branc h and a significantly different lifetime from that reported previously. The abnormally large strength of the 11(-) to 8(+) transitions in both Pb-190 and Pb-192 match those known in some light polonium isotopes, an effect whi ch is suggested to be linked to a change in structure of the orbitals in th e 8(+) configuration when oblate deformation is established; the lowest Ome ga = 7/2(-) proton Nilsson orbital changes from being predominantly of h(9/ 2) character at sphericity to a mixed f(7/2)/h(9/2) parentage at oblate def ormations, thus enabling an enhanced i(13/2) to f(7/2) octupole-coupled tra nsition.