R-Matrix Analysis of ²³⁸U High-Resolution Neutron Transmissions and Capture Cross Sections in the Energy Range 0 to 20 keV

The neutron resonance parameters of ²³⁸U were obtained from a SAMMY analysis of high-resolution neutron transmission measurements and high-resolution capture cross-section measurements performed at the Oak Ridge Electron Linear Accelerator (ORELA) in the years 1970-1990 and from more recent transmission and capture cross-section measurements performed at the Geel Linear Accelerator. Compared with previous evaluations, the energy range for this resonance analysis was extended from 10 to 20 keV, taking advantage of the high resolution of the most recent ORELA transmission measurements. The experimental database and the method of analysis are described in this paper. The neutron transmissions and the capture cross sections calculated with the resonance parameters are compared with the experimental data. A description is given of the statistical properties of the resonance parameters and of the recommended values of the average parameters. The new evaluation results in a slight decrease of the effective capture resonance integral and improves the prediction of integral thermal benchmarks by 70 to 200 pcm.