An effective two-body interaction is constructed from a new Reidlike N N potential for a large no-core space consisting of six major shells and is used to generate the shell-model properties for light nuclei from A=2 to 6. For practical reasons, the model space is partially truncated for A=6. Binding energies and other physical observables are calculated and they compare favorably with experiment.

Large-basis shell model studies of low-lying excitations in light nuclei from 4 He to 7 Li have been performed with a multivalued G-matrix effective interaction, as recently suggested by Haxton et al.. Calculations were performed relative to the vacuum ("no core") using very large, separable model spaces containing all excitations with unperturbed energies up to 8hΩ. Using G matrices derived from a new Nijmegen potential, we achieve a very satisfactory description of these excitations.

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We study the pairing energy in the ground state of a system of N particles occupying a symmetric two-level model space with a level degeneracy A. Assuming a pairing Hamiltonian, we calculate the energies of the projected BCS states, using the exact, the Kamlah, and the Lipkin-Nogami particle number projection methods. We And that conclusions regarding the quality of the B.C.S. approximation as well as various approximate projection methods, drawn from studying the N=A case alone, are not valid in the more general N g 0 case when the pairing interaction is weak.