236U resonance parameters at 5.467 eV from neutron transmission measurements using thin liquid samples

• Improvements were made to the 236U resonance at 5.467 eV.
• High accuracy neutron transmission measurements were performed.
• Thin 236U liquid samples were used to produce non-saturated resonances.
• Methods for background and experimental resolution function were developed.
• The resonance parameters and uncertainties were found using a Monte Carlo approach.

The 236U isotope is an important buildup product that is generated in the 235U fuel cycle and influences reactor neutronic calculations. The aim of the present work is to improve upon the existing neutron total cross section data for the strong 236U resonance at 5.467 eV.High accuracy neutron transmission measurements were performed using the time-of-flight technique at the Rensselaer Polytechnic Institute linear accelerator. An approach was used to fabricate thin 236U samples using liquid, allowing for non-saturated resonances. The transmission measurements were made at the 15 m flight station with a 6Li glass scintillation detector. Methods to characterize the background and experimental resolution function were developed. The 236U resonance parameters and their uncertainties at 5.467 eV were determined by fitting the transmission data using a Monte Carlo approach with the SAMMY multi-level R-matrix Bayesian code.The resonance parameters determined in this work are: energy, E, equal to 5.467 ± 0.005 eV; neutron width, Γn, equal to 2.13 ± 0.04 meV; and radiation width, Γγ, equal to 27 ± 1 meV. The fission width, Γf, was not fitted and was fixed to the ENDF-7.1 value of 0.290 meV. These parameters gave a neutron capture resonance integral of 330 ± 5 b that is lower than all of the selected evaluations: Mughabghab by 4.7%, ENDF-7.1 by 3.7%, JEFF-3.1 by 4.8%, and JENDL-4.0 by 7.2%.