Neutron Scattering Cross Section ofU235

Abstract

The neutron elastic scattering cross section for ${\mathrm{U}}^{235}$ has been measured by the "thick-thin" method over the range of neutron energies from 0.27 to 7.7 ev. The cross section rises at lower energies, the rise being qualitatively that expected if an unusually strong level were present just below the binding energy. Analysis of the data in terms of a Breit-Wigner single-level formula gives a resonant and a constant component. The solution yields a value of 10±1 barns for the constant component, which may be identified as the "potential scattering" cross section. This result is relatively insensitive to the location of the bound level and to the exact analytical form of the resonant component. The magnitude of the resonant component is not in perfect quantitative agreement with the parameters commonly quoted for the "negative energy" resonance at $E_0=-1.4\mathrm{}$ ev. This disagreement is probably not significant because of the uncertainties in the analysis of both the total and the scattering cross section.