The quantum mechanical model of the atom and the explanation it provides for the periodic table of the elements has accustomed us to the existence of shell structure in atomic properties. Thus properties such as ionisation potentials vary across the periodic table with discontinuities corresponding to the filling of shells -- degenerate sets of energy levels associated with the quantisation of orbital angular momentum in a central potential.
A surprising feature of nuclear structure is that many properties can be explained by assuming a central potential in which individual nucleons move almost independently of one another.
The existence of such a mean field can be shown by means
of the Hartree-Fock approximation.