A Precise Determination of the Total Cross Section of Uranium-235 from 0.000818 ev to 0.0818 ev

The absolute value of the total neutron cross section of U²³⁵ was measured for neutrons in the energy range 0.000818 to 0.0818 ev for two types of samples, metallic foils and D₂O solutions of uranium. Balanced solutions of U²³⁵O₂(NO₃)₂ and U²³⁸O₂(NO₃)₂ were used to determine the difference between the total cross sections of U²³⁵ and U²³⁸. This value when combined with the relatively small, known value of the total cross section for U²³⁸ gives σ_T(U²³⁵) = 695.0 ± 1.8 barns at 0.0253 ev. The measurements on the metallic U²³⁵ foils agreed with the measured total cross section determined from the liquid solution data to better than 1%, yielding σ_T(U²³⁵) = 698.7 ± 4.7 barns at 0.0253 ev. The measured value of the U²³⁵ total cross section at 0.00291 ev combined with the scattering cross section, a recent precise value of (1 + α) at 0.00291 ev, and the ratio σ_f (0.0253 ev)/σ_f (U²³⁵) = 590.8 ± 5.4 barns at the standard neutron energy of 0.0253 ev.