U(n, γ) DANCE and NEUANCE measurements at LANSCE

Uranium-233 has played an important role in critical experiments in the 50's and 60's. More recently, management of legacy ²³³U material across the DOE complex has led to a requirement for improved nuclear cross sections. 

The experimental 233U(n,γ) cross section data available in the literature are scarce. An accurate measurement of the 233U(n,γ) cross section is required by the NCSP (National Critically Safety Program) to complete the neutron-induced cross section data. Measurements of the ²³³U(n,γ) reaction data were made in 2020 and 2021 at the Los Alamos Neutron Science Center (LANSCE) using the Detector for Advanced Neutron Capture Experiments (DANCE) combined with the NEUtron detector array at dANCE (NEUANCE).

Because ²³³U fission is around one order of magnitude more likely than capture, an accurate measurement of the capture cross section relies on the discrimination between fission and capture gammas. NEUANCE tagged fission neutrons while DANCE detected capture and fission gammas. Coincidences between them are reconstructed during analysis. This measurement will provide the capture to fission ratio, reducing the uncertainties with respect to an absolute measurement by eliminating experimental complications like self-absorption, beam/target overlap and non-uniformities.