ABSTRACT
The more realistic models can be described as generalizations and extensions built on the single-particle model. Despite this model's sweeping simplifications and the neglect of intemucleon interactions, it may well be that the single-particle orbits represent fairly well an average of the actual nucleon motions. The single-particle model describes a nuclear state by stating how many nucleons are in each of the orbits. In the extreme single-particle model, all the different states that can be formed by k particles with the same have the same energy. The calculations on which the extended single-particle model is based require that the interaction be strong enough to remove the degeneracies but not so strong, compared with the spin-orbit force that j ceases to be a good quantum number for each nucleon. A large part of the actual interaction is accounted for in the single-particle shell-model potential, which represents the average effect on one nucleon of all the other nucleons.
