Integral Measurement of the 237Np($n$, γ)238Np Cross Section with Fast Neutrons

Accurate knowledge of the 237Np($n$; γ)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. A measurement of the 237Np($n$; γ)238Np cross section was performed using a well characterized fast neutron source and the results was compared with previous measurements and current nuclear data evaluations. This will provide an integral measurement that can be used as a benchmark for current evaluations. Multiple samples of 237Np were irradiated in the Godiva-IV critical assembly. Following the irradiation, the samples placed in a γ-ray counting setup and the γ-rays emitted from the decay of 238Np were measured over a time period of approximately 7 days. Multiple γ-ray decay branches of 238Np were observed. The observed activity of 238Np was used to calculate the amount of 238Np produced during the irradiation via the 237Np($n$; γ)238Np and an integral cross section of 359(10) mb was measured. The 238Np half-life has been measured with a result of 50.34(7) hours. An integral measurement of the 237Np($n$; γ)238Np cross section has been measured. This result has been compared to the calculated integral cross section using the ENDF/BVIII.0 and JENDL-4.0 evaluated cross sections and found to be in good agreement with ENDF/BVIII.0 value of 367 mb. The JENDL-4.0 evaluation yields a value of 312 mb, which is significantly lower than the measured cross section.