Evolution of the N = 20 and N = 28 shell closures in neutron-rich nuclei

摘要

The isospin dependence of shell closure phenomena is studied for light neutron-rich nuclei within a microscopic self-consistent approach using the Gogny force. Introducing configuration mixing, ~(32)Mg is found to be dynamically deformed, although the N = 20 spherical shell closure persists at the mean-field level for all N = 20 isotones. In contrast, the N = 28 spherical shell closure is found to disappear for N - Z ≥ 10 whereas deformed shell closures are preserved and lead to shape coexistence in ~(44)S. Configuration mixing shows that the ground state of this nucleus is triaxially deformed. The first 2~+ excitation energy E_x = 1.46 MeV and the reduced transition probability B(E2; 0_(gs)~+ → 2_1~+)= 420 e~2 fm~4 obtained with our approach are in good agreement with experimental data.