Fission Cross Section ofU235for Fast Neutrons

An absolute measurement of the fission cross section of ${\mathrm{U}}^{235}$ for 1.27-Mev neutrons has been made. The neutron flux was measured with a recoil-proton proportional counter using a thin solid radiator of hydrogenous material. In addition, relative cross sections have been measured between 0.403 and 1.620 Mev. These relative measurements also utilized a recoil-proton flux monitor. The cross section has a constant value of 1.27±0.044 barns in the neutron-energy interval between 1.0 and 1.5 Mev.