Nuclear structure near the doubly-magic 100Sn

The single particle (hole) energies in 100Sn, as extrapolated by a shell model analysis of the neighboring nuclei, show a remarkable similarity to those in 56Ni, one major shell lower. This is borne out in nearly identical Iπ=2+ excitation energies, implying E(2+)≃3 MeV in 100Sn, and a large neutron effective E2 charge e⩾1.6e. In contrast a small proton polarization charge δe⩽0.3e is found, pointing to a large isovector charge. Mean field predictions for single particle energies show substantial deviations from the experimental extrapolation. From the experimental two-proton hole spectrum in 98Cd an improved empirical interaction is extracted for the π(p1/2,g9/2) model space yielding a good description of the N=50 isotones 95Rh to 98Cd. In 104Sn, for the first time in this region, strong E3 transitions with B(E3)⩾17 W.u. were identified, indicating E(3−)≃3 MeV in 100Sn. New experimental devices, as the Ge-cluster cube and total absorption spectrometers, applied in a pioneering experiment to the β+/EC deca...