In nuclear physics, the nuclear shell model is a theoretical model to describe the atomic nucleus. The nuclear shell model was proposed by Dmitry Ivanenko in 1932 and further developed independently by several physicists such as Maria Goeppert-Mayer, Eugene Paul Wigner and J. Hans D. Jensen in 1949. It must be noted this model is based on the Pauli exclusion principle to describe the structure of the nucleus in terms of energy levels.
The nuclear shell model is partly analogous to the atomic shell model which describes the arrangement of electrons in an atom, in that a filled shell results in greater stability. Nucleons are added to shells which increase with energy that orbit around a central potential. In the atomic shell model the central potential around which the electrons orbit is generated by the nucleus. Nucleons are added to shells which increase with energy that orbit around a central potential.
In comparison to atomic shell model, the atomic nucleus governed by two different forces. The residual strong force, also known as the nuclear force, acts to hold neutrons and protons together in nuclei. In nuclei, this force acts against the enormous repulsive electromagnetic force of the protons. The term residual is associated with the fact, it is the residuum of the fundamental strong interaction between the quarks that make up the protons and neutrons. The strong interaction is very complicated interaction, because it significantly varies with distance. At distances comparable to the diameter of a proton, the strong force is approximately 100 times as strong as electromagnetic force. At smaller distances, however, the strong force between quarks becomes weaker, and the quarks begin to behave like independent particles. In particle physics, this effect is known as asymptotic freedom.
With the enormous strong force acting between individual nucleons and with so many nucleons to collide with, how can nucleons orbit a central potential without interacting? This problem is explained by the Pauli exclusion principle, which states that two fermions cannot occupy the same quantum state. In other words, the interaction will not occur, if the higher energy shells are fully occupied and the energy imparted to the nucleon during the collision is insufficient to promote the nucleon to an unfilled orbit. As a result, the nucleons orbit independent of one another.
The nuclear shell model was able to describe many phenomena like the magic numbers, the ground state spin and parity etc..