GENERALIZED BETHE FORMULA (GBF) AND COMBINATORIAL CALCULATIONS FOR THE SYSTEMATICS OF PB NUCLEI

Total level densities and state densities up to 40 MeV of excitation e nergy are calculated combinatorially for the systematics of Pb nuclei using independent nucleons in the realistic single particle spectra. T hese combinatorial level densities are well fitted by GBF, both for do ubly closed shell nucleus Pb-208 and away from the shell closure. The corresponding GBF parameters exhibit smooth behavior with the change o f the neutron number N, having pronounced extrema at the double shell closure. The GBF fit to the combinatorial results is compared with the fit of standard Bethe formula (BF) and of the Ignatyuk formula. (C) 1 997 Elsevier Science B.V.