P.G. Young and E.D. Arthur

Los Alamos National Laboratory, Los Alamos, New Mexico, USA

Cross sections for neutron-induced reactions on 235U between 0.01 and 20 MeV have been calculated in a preliminary analysis for the ENDF/B-VI evaluation, with particular emphasis on neutron inelastic scattering. A deformed optical model potential that fits total, elastic, inelastic, and low-energy average resonance data is used to calculate direct (n,n') cross sections and transmission coefficients for a Hauser-Feshbach statistical theory analysis using a multiple fission barrier representation. Direct cross sections for higher-lying vibrational states are provided from DWBA calculations, normalized using B(El) values determined from (d,d') and Coulomb excitation data. Initial fission barrier parameters and transition state density enhancements appropriate to the compound systems involved were obtained from previous analyses, especially fits to charged-particle fission probability data. Further modifications to fit 235U(n,f) data were small, and the final fission parameters are generally consistent with published values. The results from this preliminary analysis are compared with the ENDF/B-V evaluation as well as with experimental data.

KEYWORDS: 235U, neutron reactions, data evaluation, nuclear models, coupled-channel optical model, fission theory