PNNL

Abstract

Background: Accurate knowledge of the 237Np(n, ?)238Np cross section at fast neutron energies is important for applied nuclear science. The presently available experimental data has large disagreements in the fast neutron region. Purpose: Perform a model-independent measurement of the 237Np(n, ?)238Np integral cross section using a well characterized fast neutron source and compare the result with previous measurements and current nuclear data evaluations. Provide an integral measurement that can be used as a benchmark for current evaluations. Methods: Multiple samples of 237Np were irradiated in the Godiva-IV critical assembly. Following the irradiation, the samples placed in a ?-ray counting setup and the ?-rays emitted from the decay of 238Np were measured over a time period of approximately 7 days. Multiple ?-ray decay branches of 238Np were observed. Results: The observed activity of 238Np was used to calculate the amount of 238Np produced during the irradiation via the 237Np(n, ?)238Np reaction and an integral cross section of 342(11) mb was measured for the Godiva-IV neutron spectrum. The 238Np half-life has been measured with a result of 50.31(5) hours. Conclusion: The 237Np(n, ?)238Np integral cross section measured in this work is in agreement with overlapping 1s error bands to ENDF/B-VIII.0. However, the measured value is 3s away from the calculated integral cross section using JENDL-5. This measurement offers a reliable benchmark for future 237Np(n, ?)238Np cross section evaluations.