PARTICLE-HOLE STATE DENSITIES IN PREEQUILIBRIUM NUCLEAR-REACTION MODELS

The particle-hole level and state densities required to calculate the cross sections of preequilibrium nuclear reactions are reviewed, Using the equidistant spacing model, explicit expressions are found for the total density of states and for the density of final accessible state s. These are modified to take account of the restrictions due to the P auli principle and the finite depth of the nuclear potential. The depe ndencies of the densities on spin, isospin, linear momentum and pairin g are described. The effects of departures from the equidistant spacin g model, particularly those;due to shell structure, are also discussed . Some comparisons are made with realistic densities obtained by full combinatorial calculations Some recommendations are made concerning th e best choices to be made for pre-equilibrium calculations, combining accuracy and convenience.