Structure of Light Neutron-Rich Nuclei and Important Roles of Tensor Interaction

Structure of light neutron-rich nuclei are investigated by shell model calculations with the use of our new shell model Hamiltonians. The new Hamiltonians take into account important roles of the tensor interaction, and can explain well the Gamow-Teller (GT) transitions in nuclei with mass 14 and 12. A new version with repulsive corrections in T=1 monopole terms is applied to study structure of neutron-rich carbon isotopes. Characteristics of effective neutron single particle enrgies and shell evolutions toward the drip-line are discussed. Ground state energies and low lying energy levels of the isotopes are found to be well reproduced. The anomalous quenching of the magnetic dipole (M1) transition strength in C-17 is also found to be well explained. GT transitions in C-19 are studied. The halo nature of C-19 is investigated from a retarted GT transition. Contributions from three-nucleon forces induced by Delta excitations are shown to be the main origin of the repulsive monopole corrections in the T=1 channel.