Thresholds for Fast Neutron Fission in Thorium and Uranium

The threshold energy for fast neutron fission of thorium and uranium has been measured by using the neutrons from thin lithium films through the ${\mathrm{Li}}^7\mathrm{}(p,n)\mathrm{}$ reaction. Neutron energy fission thresholds were found to be 1.0±0.1 Mev for ${\mathrm{U}}^{238}$ and 1.10±0.05 Mev for ${\mathrm{Th}}^{232}$.