Neutron total and capture cross section of 232Th from 0.006 to 18 eV. Final report

Transmission measurements were carried out to determine the total cross section by use of high-purity thorium metal and a 6Li-glass scintillation detector. To determine the capture cross section, the relative neutron capture yield was found. Capture events were measured by a 1.25-m-dia liquid scintillator at a flight path of 25.68 m. The relative neutron flux is measured with a 10B4C-NaI detector at a flight path of 28.32 m. The measured capture yield is converted to the capture cross section by making corrections for multiple scattering and self-shielding. Both the experimental total and capture cross sections are reproduced significantly better by ENDF/B-V than ENDF/B-IV in the energy region above 0.1 eV. There is substantial agreement in this energy range between the present capture results and the results of a recent measurement at BNL. For neutron energies below 0.1 eV, the cross section measurements are strongly influenced by microcrystalline effects in the samples (the capture data are affected via multiple scattering). The experimental data total cross section increases with decreasing energy less rapidly than the ENDF/B-V evaluated total cross section for energies less than 0.1 eV. Bragg scattering effects are predicted and observed in the total cross section data below about 0.4 eV. 51 figures, 13 tables