Observation of positive-parity bands in 109Pd and 111Pd: Enhanced γ softness

The neutron-rich nuclei Pd-109 and Pd-111 were produced as fission fragments following the Si-30 + Er-168 reaction at 142 MeV. Using the identification based on the coincidences with the complementary fission fragments, the only positive-parity bands observed so far in Pd-109 and Pd-111 emerged from this work. A band, built on top of the 5/2(+) ground state exhibiting Delta I = 1 energy-level staggering, was observed in each of these nuclei. Both nuclei of interest, Pd-109 and Pd-111, are suggested to lie in the transitional region of Pd isotopes of maximum gamma softness. The ground states of both nuclei are predicted by total Routhian surface calculations to be extremely gamma soft with shallow triaxial minima. The first crossing in the new bands is proposed to be attributable to an alignment of h(11/2)(2) neutrons.