Shape coexistence in neutron-deficient Pb nuclei probed by quadrupole moment measurements

The spectroscopic quadrupole moments of the 11− and 12+ isomers in 192,194Pb, described by the 3s1/2−21h9/21i13/2 intruder two-proton and 1i13/22 two-quasineutron configurations, respectively, have been determined by the method of time-differential observation of the γ-ray perturbed angular distribution. The derived values are |Qs|(12+,192Pb) = 0.32(4) eb, |Qs|(11−,192Pb) = 2.9(3) eb and |Qs|(11−,194Pb) = 3.6(4) eb. The 8+ 2304 keV and 9− 2514 keV states in 192Pb have been identified as isomers, with half-lives of 3.9(3) and 3.3(2) ns, respectively. The experimental spectroscopic quadrupole moments for the 11− and 12+ isomers in neutron deficient Pb nuclei have been described in the framework of the pairing plus quadrupole model. The intrinsic quadrupole moments and deformation of the 11− isomers are compared with the predictions of mean-field and interacting boson models.