ABSTRACT
States of nucleons moving independently in a central potential well have usually large degeneracies. In the case of closed shells there is a single state with total angular momentum J = 0. States of one nucleon outside closed shells have also well defined spins equal to that of the single nucleon. The same is true for states in which one nucleon is missing from closed shells. These are single hole states which will be considered later in detail. Whenever there are several nucleons outside closed shells there are several states which are allowed by the Pauli principle. If the Hamiltonian includes only the kinetic energies of nucleons and their potential energy in the central well, all such states are degenerate. A look at any nuclear level scheme clearly demonstrates that energy levels are far from degenerate. This should not be surprising since the central potential cannot replace exactly the mutual interactions of the nucleons.
