Sensitivity of Computed Uranium-238 Self-Shielding Factors to the Choice of the Unresolved Average Resonance Parameters

The influence of different representations of the unresolved resonances of ²³⁸U on the computed self-shielding factors is examined. It is shown that the evaluated infinitely diluted average capture cross section does not provide sufficient information to determine a unique set of unresolved resonance parameters; different sets of unresolved resonance parameters equally consistent with the evaluated average capture cross section yield significantly different computed self-shielding factors. In the conclusion it is recommended that the resolved resonance description of the evaluated ²³⁸U cross sections be extended to higher energies and that thick sample transmission data and self-indication data be used to improve the evaluation of the unresolved resonance region.