SHELL-MODEL COMBINATORIAL CALCULATIONS OF NUCLEAR LEVEL DENSITIES

Spin-dependent nuclear level densities were calculated for selected nuclides. In each case the numbers and spins of the levels were determined from a computer-generated list of all contributing shell-model configurations. To calculate the energies of the configurations, we assumed the model nucleus to be an infinitely deep spherical well containing fermions that are noninteracting except for pairing forces, for which the BCS theory was used. Comparisons of the calculated results with experimental level densities for odd, even, and odd-mass nuclides show reasonable agreement for nuclides with A>50. The results of calculative investigations of the effects of shell closings, pairing, etc., and the persistence of these effects to high excitation energies and angular momenta are reported and discussed. Comparisons of these results with those obtained from the most commonly used algebraic formula show significant disagreements in the curvature of the logarithmic energy dependence and in the spin distributions. © 1969 The American Physical Society.