Nuclear structure far off stability and implications for nuclear astrophysics

The shell structure of 100Sn as inferred from prompt and delayed γ-ray spectroscopy with multidetector γ-arrays in-beam and at ISOL and in-flight separators shows close resemblance to 56Ni one major shell lower. The results of large-scale shell model calculations employing realistic interactions derived from effective NN potentials by G-matrix theory will be confronted with experimental evidence from β-decay and in-beam data with emphasis on seniority and spin-gap isomers, highlighting the role of core excitations. Key examples from recent experiments are 94,95Ag and 98Cd. The dominant monopole interaction of the spin-flip partners πg9/2 - νg7/2 in N = 50,51 isotones below 100Sn is echoed in the πf5/2 - νg9/2 pair of nucleons, which is decisive for the N = 50 shell gap in 78Ni. The persistence of the N = 50 shell and the weakness and extreme locality of the N = 40 shell in 68Ni can be traced back to monopole driven migration of selected single particle orbits. Recent experimental data on 70,72,76Ni, 78Zn and 67Fe give evidence for this scenario. The implication of these strong monopole shifts for the shell quenching in neutron-rich N = 50,82 isotones as invoked to explain astrophysical r-path abundances is discussed. (author)