Structures of Light Neutron-Rich Nuclei with Orbit--Orbit Coupling

The properties of N=7, 8, 9 isotones with Z=4-8 are studied in the framework of the single-particle shell model. A tentative orbit--orbit coupling is introduced in the average nuclear potential. Calculations give a unified description of the
structures of N=7,8,9 isotones. The neutron level inversion in N=7 and N=9 isotones is discussed. The ground-state level inversion in ¹¹Be and ¹⁵C is reproduced. The inversion between 2s _1/2 and 1d _5/2 neutron levels in ¹⁴B and ¹³Be is predicted. The possible halo structures in N=7 and N=9 isotones are analysed. The numerical results confirm the one-neutron halo structures in ¹¹Be(2s _1/2), ¹¹Be(1p _1/2), ¹²B(2s _1/2), ¹³C(2s_1/2),¹⁴B(2s_1/2) and ¹⁵C(2s_1/2). The study implies that the attempt of considering orbit--orbit interaction in the shell model may be a feasible way to explain the anomalous
properties of exotic light nuclei.