Rintaro Fujimoto

Magic Numbers in Exotic Nuclei and Spin-Isospin Properties of the NN Interaction

The magic numbers in 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. 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 the lightest exotic nuclei to nucleosynthesis of heavy elements.

Frontiers and challenges of nuclear shell model

Abstract:Two recent developments of the nuclear shell model are presented. One is a breakthrough in computational feasibility owing to the Monte Carlo Shell Model (MCSM). By the MCSM, the structure of low-lying states can be studied with realistic interactions for a wide, nearly unlimited basically, variety of nuclei. The magic numbers are the key concept of the shell model, and are shown to be different in exotic nuclei from those of stable nuclei. Its novel origin and robustness will be discussed.

New aspects of spin degrees of freedom in nuclei

Abstract New aspects of quenching effects in Gamow-Teller (GT) transitions and magnetic moments are investigated for p-shell nuclei using an improved shell-model Hamiltonian with enhanced spin-flip neutron-proton interaction and modified single-particle energies. Here, the improved shell model Hamiltonian is used in the configuration space up to 2–3 ħw excitations to study spin dependent transitions. Manifestation of less quenching due to a weakening of intermediate coupling nature of the Cohen-Kurath Hamiltonian is shown in GT transitions; 12 C → 12 N, 11 B → 11 Be and 9 Li → 9 Be. Better agreement with experimental values is obtained by using the present Hamiltonian in most of GT transitions and magnetic moments in p-shell nuclei.

SHELL FORMATION AND DISAPPEARANCE IN EXOTIC NUCLEI AROUND N = 20

The disappearance and the appearance of the magic numbers in N ∼ 20 unstable nuclei are discussed with large-scale shell-model calculations, most of which are the Monte Carlo shell model (MCSM) calculations. The MCSM calculations turn out to give a systematic description for this region. The origin of the shift of the magic structure from N =16 to 20 is shown to be the spin-isospin dependence of the nucleon-nucleon interaction giving rise to strongly attractive T =0 monopole interaction between the 0d5/2 and the 0d3/2. The extreme location of fluorine drip line can be understood from the viewpoint of the varying N =20 shell gap.