Note on the Fast-Neutron Total Cross Section of Thorium

The energy-averaged neutron total cross sections of thorium were measured from ∼0.1 to 5.0 MeV with statistical accuracies of ≤2%. The experimental results are larger than the values given in ENDF/B-IV by as much as 10 to 15% in energy regions of prime relevance to thorium-²³³U fast fission reactor concepts. These large differences imply major changes in evaluated neutron cross sections essential for thorium cycle neutronic assessments. All measured data reported have been transmitted to the National Nuclear Data Center, Brookhaven National Laboratory.