Spectroscopy of 82188Pb106: Evidence for shape coexistence

In-beam γ-ray spectroscopy of 188Pb has been carried out using Gammasphere. Time-correlated γ-γ coincidence methods have allowed the identification of new structures above and below the two-particle isomeric states. The detailed decay of the proposed Kπ=8-, 1 μs isomer has been established, together with a rotational band based on the isomer. Both decay and band properties confirm the association with a prolate deformation and the two-quasineutron 9/2+[624]x7/2-[514] configuration. The band structure identified above the 11- isomer from the two-proton configuration 9/2-[505]x13/2+[606] has a moment of inertia similar to those of the bands known in heavier isotopes and to the one-quasiproton components, but the perturbations and in-band properties are not as expected for a simple, symmetric oblate deformation. This structure is fed by a (19-) isomer. Possible configurations for this and other multiquasiparticle states are discussed in the context of multi-quasiparticle calculations for coexisting deformations. Low-spin structures populated partly from the decay of the 8- isomer have also been identified. Several of these may be associated with proposed excited 0+ states. Their properties, including yrare-yrast E0 decays and gamma-ray branching ratios, are analyzed using band-mixing models. These and other analyses support a shape coexistence scenario, with some qualifications