INELASTIC NEUTRON-SCATTERING BY U-235 AND U-238 NUCLEI

Inelastic scattered neutron spectra and fission neutron spectra for U-235 and U-238 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 U-235(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 fetal inelastic scattering cross sections, and the inelastic scattered neutron spectra were derived. The results of this work confirm the ENDF/B-VI evaluations for U-235. The total inelastic cross sections for U-238 are very close to those of ENDF/B-V/I. However, substantial discrepancies exist between our experimental data for U-238 and the ENDF/B-V/I and JENDL-3 evaluations concerning the excitation functions for levels between 0.5 and 1.2 MeV and continuum spectra.