Lead 207, 208 (n, xn gamma) reactions for neutron energies up to 200 MeV

摘要

High-resolution (gamma)-ray spectra from the interaction of neutrons in the energy range from 3 to 200 MeV with (sup 207,208)Pb were measured with the white neutron source at the WNR facility at Los Alamos National Laboratory. From these data, excitation functions for prominent (gamma) transitions in (sup 200,202,204,206,207,208)Pb were derived from threshold to 200 MeV incident neutron energy. These (gamma)-production cross sections represent formation cross sections for excited states of the residual nuclei. The results are compared with the predictions of nuclear reaction calculations based on the exciton model for precompound emission, the Hauser-Feshbach theory for compound nuclear decay, and coupled channels calculations to account for direct excitation of collective levels. Good agreement was obtained over the entire energy range covered in the experiment with reasonable model parameters. The results demonstrate that multiple preequilibrium emission has to be taken into account above about 40 MeV, and that the level density model of Ignatyuk should be used instead of the Gilbert-Cameron and back-shifted Fermi-gas models if excitation energies exceed about 30 MeV.