Observation of a core-excited E4 isomer in 98Cd -: art. no. 064304

A core-excited I-pi=(12(+)) spin-gap isomer was identified in Cd-98 in an experiment at EUROBALL IV. It was found to feed the known I-pi=(8(+)) seniority isomer by an E4 transition. Half-lives of T-1/2=0.23 ((+4)(-3)) mus and 0.17 ((+6)(-4)) mus were measured for the two states at E-x=6635 keV and 2428 keV, respectively. From the excitation energy of the core-excited isomer a Sn-100 shell gap of 6.46(15) MeV is inferred. The measured E4 and E2 strengths, Sn-100 core excitations and the origin of empirical polarization charges are discussed in the framework of large-scale shell model calculations. An E2 polarization charge for protons of deltae(pi)<0.4 e is found, which corresponds to the empirical value deltae(pi)=0.45((+20)(-25)) e in the pure proton hole valence space.