Quasiclassical theory of nuclear shell structure. [Clssical motion]

The quasiclassical approximation for the density of single-particle levels based on Feynman path integrals is extended to the case of degenerate classical motion. It is shown that the appreciable fluctuations (gross shells) in the density of the single-particle levels correspond to quasiclassical quantization of the motion in multidimensional periodic orbits. Formal estimates are obtained for the scale and period of the oscillations of the single-particle level density, the level density of an excited nucleus, and the shell corrections to the binding energies and deformation energies of nuclei. The connection between the classical theory and the method of numerical averaging is discussed.