Subthreshold Fission Cross Section of ²³⁷Np

An experimental program has been developed at Los Alamos Neutron Science Center to precisely measure fission cross sections relevant to advanced nuclear reactor designs and transmutation concepts. The first completed measurement is of ²³⁷Np(n,f), and the subthreshold part of the measurement is reported here. The JENDL-3.3 evaluation agrees well with the experimental results in the unresolved resonance region, where a discrepancy between the ENDF/B-VI and JENDL-3.3 evaluations exists.