Nuclear structure near the doubly-magic 100Sn

The single particle (hole) energies in Sn-100, as extrapolated by a shell model analysis of the neighbouring nuclei, show a remarkable similarity to those in Ni-56, major shell lower. This is borne out in nearly identical I-pi = 2(+) excitation energies, implying E(2(+))similar or equal to 3 MeV in Sn-100, and a large neutron effective E2 charge e greater than or equal to 1.6e. In contrast a small proton polarisation charge Se less than or equal to 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 Cd-98 an improved empirical interaction is extracted for the pi(p(1/2),g(9/2)) model space yielding a good description of the N = 50 isotones Rh-95 to Cd-98 In (104) Sn, for the first time in this region, strong E3 transitions with B(E3)greater than or equal to 17 W.u. were identified, indicating E(3(-))similar or equal to 3 MeV in 100Sn. New experimental devices, as the Ge-cluster cube and total absorption spectrometers, applied in a pioneering experiment to the beta(+)/EC decay of Ag-97, have led to a consistent picture of the Gamow-Teller quenching around 100Sn. The experimental results are discussed in the framework of various shell model approaches by using both empirical and realistic interactions.