Spherical and deformed isomers in188Pb

Several isomers in ${}^{188}\mathrm{Pb}$ have been identified using pulsed beams, the recoil-shadow technique, and the ${}^{164}\mathrm{Er}{(}^{28}\mathrm{Si}{,4n)}^{188}\mathrm{Pb}$ 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 $1.2\hspace{0.5em}\mu \mathrm{s}$ leads via a complicated path to the $8^{+}$ and lower spin yrast states. It is a candidate for the $K^{\pi }{=8\mathrm{}}^{-},$ two-quasineutron state which occurs systematically in $N=106\mathrm{}$ prolate-deformed nuclei, supporting the assumption that the intruding collective well is prolate.