The origin of the spin-orbit splitting in some light nuclei using a modified interaction

The spin-orbit splittings in the spectra of nuclei with A = 5, 15, and 17 have been restudied, with a new set of matrix elements, within the framework of the shell model with core excitations. Investigated are the dependences of these splittings on core-excitation and on some of the different components of the nucleon- nucleon interaction. Our work confirms that the two-body spin-orbit interaction has a major effect whose magnitude depends on the size of the model space that is used. The effect of the tensor interaction is again seen to be considerably less important.