Nuclear structure far off stability-Implications for nuclear astrophysics

The single-particle structure and shell gap of Sn-100 as inferred from previous in-beam gamma-ray spectroscopy has been confirmed in recent studies of seniority and spin-gap isomers by gamma gamma, beta gamma, beta p gamma, p gamma and 2p gamma spectroscopy. The results for Ag-94,Ag-95, Cd-98 and its N = 50 isotones Pd-96 and Ru-94 stress the importance of large-scale shell model calculations employing realistic interactions for the isomerism, np-nh excitations, seniority mixing and E2 polarisation of the Sn-100 core. The strong monopole interaction of the Delta l = 0, 1 spin/isospin-flip partners pi g(9/2)-Vg(7/2) along the N = 50 isotones and the pi f(5/2)-Vg(9/2) pair of nucleons along the Z = 28 Ni isotopes are decisive for the evolution of the shell structure towards Sn-100 and Ni-78. It can be traced back to the tensor force in the effective nucleon-nucleon interaction and provides a straightforward explanation for new shells in neutron-rich light nuclei, implying qualitative predictions for new N = 32, 34 subshells in Ca isotopes, persistence of the Ni-78 proton and neutron shell gaps and non-equivalence of the g(9/2) valence mirror Ni isotopes and N = 50 isotones. This is corroborated by recent experimental data on Cr-56,Cr-58 and Ni76-76. The implication of monopole driven shell evolution for apparent spin-orbit splitting towards N >> Z and structure along the astrophysical r-path between N = 50 and N = 82 is discussed.