Shell, shape and spin/isospin structures of exotic nuclei

Abstract

The magic numbers and shell structure of exotic nuclei are discussed, and their novel origin is shown to be the spin-isospin dependent part of the nucleon-nucleon interaction in nuclei. The importance and robustness of this mechanism is shown in terms of meson exchange, G-matrix and QCD theories. The analytic expression of the monopole components of the τ·τ σ·σ interaction is presented for the first time, showing a strong attraction between spin-flip partners of a proton and a neutron. In neutron-rich exotic nuclei, magic numbers such as N=8, 20, etc., can disappear, while N=6, 16, etc., arise, affecting the structure of lightest exotic nuclei to nucleosynthesis of heavy elements. Effects due to the variation of the shell gap are discussed, in particular on the excitation energies and B(E2) values of 32,34Mg exotic nuclei. It is suggested that various anomalous properties of exotic nuclei can be studied with the paradigm of shell evolution.