Spherical and Deformed Isomers in 188Pb

Several isomers in 188Pb have been identified using pulsed beams, the recoil-shadow technique, and the 164Er(28Si,4n) 188Pb reaction. Two of the isomers feed the 10+ state of the yrast sequence and are suggested to be the 11- and 12+ states from oblate and spherical configurations, respectively. The 12+ isomer is fed weakly by another isomer with a relatively long lifetime, but it has not been characterized. A fourth isomer with a lifetime of about 1.2 μs leads via a complicated path to the 8+ and lower spin yrast states. It is a candidate for the Kπ=8-, two-quasineutron state which occurs systematically in N=106 prolate-deformed nuclei, supporting the assumption that the intruding collective well is prolate