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

摘要

The spectroscopic quadrupole moments of the 11(-) and 12(+) isomers in Pb-192,Pb-194, described by the 3s(1/2)(-2)1h(9/2)1i(13/2) intruder two-proton and 1i(13/2)(2) two-quasi neutron configurations, respectively, have been determined by the method of time-differential observation of the gamma-ray perturbed angular distribution. The derived values are vertical bar Q(s)vertical bar(12(+),Pb-192) = 0.32(4) eb, vertical bar Q(s)vertical bar(11(-),Pb-192) = 2.9(3) eb and vertical bar Q(s)vertical bar(11(-),Pb-194) = 3.6(4) eb. The 8(+) 2304 keV and 9(-) 2514 keV states in Pb-192 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. (C) 2007 Elsevier B.V. All rights reserved.