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 K^π=8^-, two-quasineutron state which occurs systematically in N=106 prolate-deformed nuclei, supporting the assumption that the intruding collective well is prolate.