This manuscript details the successful measurement, and subsequent analysis, of the uranium-236(n,g) radiative capture kernels in the resolved resonance region, of importance to the thorium fuel cycle.
The experiment took advantage of the convenient features of the CERN n_TOF facility. Features such as a fully digital DAQ, high instantaneous neutron flux, and the powerful background rejection capabilities offered by the BaF2 Total Absorption Calorimeter (TAC) detector, owing to its near 4 pi solid angle coverage and high segmentation. These features, coupled with a high purity (99.85%) U-236 sample, resulted in the successful measurement of the radiative kernels to within 10%.
Having successfully extracted the radiative kernels up to 1500 eV with the R-matrix code SAMMY, and accounted for all sources of uncertainty, is was possible to quantify the total uncertainty for the radiative kernels. In this manner, the uncertainties were found to range from 2.3%, for resonances with little scattering and pile-up, to 5.3% for resonances with more significant scattering and pile-up effects. Hence not only was the goal of achieving the requested accuracy of 10% achieved, but even reaching the desired 5%.
Given the limited data available for this reaction, it is of value to be able to contribute the results of the current work to the nuclear data community to bolster the information currently available for the U-236 neutron capture cross section. Comparison with the latest versions of three of the major libraries, our cross section is in overall agreement with JEFF-3.2, 6% larger than JENDL-4.0 and 20% larger than ENDF/B-VII.1. These are sizable differences considering our accuracy of just 2-5%, suggesting that some revision of the libraries may be in order.
