Structures of ligth 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 2s1/2 and 1d5/2 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(2s1/2), 11Be(1p1/2), 12B(2s1/-2), 13C(2s1/2), 14B(2s1/2) and 15C(2s1/2). 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. (authors)