The Thermal-Neutron Scattering Cross Sections of Uranium-233 and Thorium-232

Neutron scattering cross sections have been measured for ²³³U and ²³²Th, using rolled metal samples, in a moderated spectrum from a 5-mg ²⁵²Cf source. The scattered neutrons were detected by two ³He detectors in an annular geometry. The experimental data were corrected for thermal and epithermal fissions, epi-thermal scattering, air scattering, room background, and self-absorption. The self-absorption corrections for the four ²³³U targets, covering a wide range in thickness, were obtained from Monte Carlo calculations. Absorption corrections for the two ²³³Th targets were avoided by using standards having the same absorption thicknesses. The results obtained were 12.30 ± 0.70 b for ²³³U and 12.78 ± 0.30 b for ²³²Th relative to vanadium with an assumed scattering cross section of 5.02 ± 0.10 b. The corresponding values for the ENDF/B-III file are 14.06 and 11.92 b, respectively.