High Resolution Fission Cross Section of Uranium-235 from 20 eV to 100 keV

The fission cross section of ²³⁵U has been measured with a nominal resolution of 1 nsec/m from 20 eV to 100 keV. Structure is seen over the entire range with fluctuations as great as 40% in the range 10 to 100 keV. These measurements have an average absolute accuracy of 8% and are based upon the ⁶Li(n, α) cross section. Some questions are raised concerning existing cross sections that assume smooth energy variation in the region of 10 to 50 keV.