First Results on

A new 238U(n,f) prompt fission neutron spectra (PFNS) measurement has been recently performed at the WNR facility of the Los Alamos National Laboratory. The measurement allows one to explore the dependence of the prompt fission neutron energy spectra on the incident neutron energy. The experimental setup couples the Chi-Nu scintillator array to a newly developed fission chamber, characterized by an improved alphafission discrimination and time resolution, a reduced amount of matter in the neutron beam and a higher actinide mass. The dedicated setup and the high statistics collected allow us to obtain a good precision on the measured fission neutron energy, as well as to explore the low energy region, down to 650keV, and the high energy region, above 5 MeV, of the emitted neutron spectrum. These are indeed the regions where discrepancies in the evaluated PFNS data are found. We present here the first preliminary results of the experiment