Spherical and deformed isomers in Pb-188 - art. no. 014303

Several isomers in Pb-188 have been identified using pulsed beams, the reco il-shadow technique, and the Er-164(Si-28,4n) Pb-188 reaction. Two of the i somers feed the 10(+) state of the yrast sequence and are suggested to be t he 11(-) and 12(+) states from oblate and spherical configurations, respect ively. The 12(+) isomer is fed weakly by another isomer with a relatively l ong lifetime, but it has not been characterized. A fourth isomer with a lif etime of about 1.2 mu s leads via a complicated path to the 8(+) and lower spin yrast states. It is a candidate for the K-pi = 8(-), two-quasineutron state which occurs systematically in N = 106 prolate-deformed nuclei, suppo rting the assumption that the intruding collective well is prolate.