EXCITATION-ENERGY AND ANGULAR-MOMENTUM DEPENDENCE OF NUCLEAR-LEVEL DENSITIES AND SPIN CUTOFF FACTOR IN SPA AND SPA+RPA APPROACHES

We investigate the excitation energy (E) and angular momentum (J) dep endence of nuclear level density and spin cut-off factor (sigma) withi n microscopic approaches based on SPA and its extension SPA+RPA repres entation of the grand partition function for quadrupole-quadrupole int eraction model Hamiltonian. For Sn-110, we find that excitation energy dependence of the total level density obtained within these approache s is significantly different. On the other hand, these approaches yiel d similar behaviour for J-dependence of the level density at fixed val ues of E. Values of sigma(SPA+RPA) at low E*are found to be slightly smaller than sigma(SPA) but they tend to become almost the same at hig her E(> 30 MeV). We also find that Bethe's formula for fixed-J level density based on the spin cut-off approximation can be used to compute rho(E, J) near the yrast line provided one uses an appropriate value of the spin cut-off factor. (C) 1998 Elsevier Science B.V.