Measurement of the 239Pu(n, f) cross section from 4 keV to 100 MeV using the white neutron source at the CSNS Back-n facility

The neutron-induced fission cross section of 239Pu was measured relative to 235U(n, f ) at the back-streaming white neutron beam line (Back-n) of the China Spallation Neutron Source (CSNS). A multicell fast fission ionization chamber was used to perform the measurement. The reliability of the measurement was verified by the high consistency of 235U's resonances between the measurement and the evaluation data. The 239Pu fission cross sections from 4 keV to 100 MeV are obtained with 1.7-5.8 % uncertainty when unfolding uncertainties are excluded. The total uncertainties including the unfolding errors, which reflect the effect of the double-bunch unfolding method, are 2.6-15 % from 10 keV to 100 MeV.