Inelastic Neutron Scattering by ²³⁵U and ²³⁸U Nuclei

Inelastic scattered neutron spectra and fission neutron spectra for ²³⁵U and ²³⁸U at incident neutron energies of 1.17, 1.79, and 2.19 MeV were measured by the neutron time-of-flight spectrometer at the Institute of Physics and Power Engineering. A solid tritium target was used as the neutron source. The experimental data were simulated by a Monte Carlo code. The interaction of beam protons inside the target, the reaction kinematics, and multiple scattering in the samples were taken into account. The data were normalized with respect to the C(n,n) and ²³⁵U(n,f) standard reaction cross sections. The experimental results were verified against absolute fission spectrum measurements by using well-known fission cross-section and v values. The Maxwell distribution parameters for the fission spectra, the total inelastic scattering cross sections, and the inelastic scattered neutron spectra were derived. The results of this work confirm the ENDF/B-VI evaluations for ²³⁵U. The total inelastic cross sections for ²³⁸U are very close to those of ENDF/B-VI. However, substantial discrepancies exist between our experimental data for ²³⁸U and the ENDF/B- VI and JENDL-3 evaluations concerning the excitation functions for levels between 0.5 and 1.2 MeV and continuum spectra.