Measurement of Fission Spectrum at LANSCE for the Evaluation of Safeguards Data

Measurements have been performed at Los Alamos Neutron Science Center (LANSCE) to acquire neutron spectra of fissile isotopes in the energy range between 0.5 and 10 MeV where the currently available experimental data are not as well-known, i.e. in the energy range less than 1 and above 5 MeV. Organic liquid scintillation detectors (EJ-309) were used. These de- tectors can be used at different thresholds enabling the observation of different neutron-energy ranges. Together with a digital data acquisition system, detailed data can be recorded and an- alyzed in a manner suitable to the specific task. The detectors show excellent pulse shape discrimination capabilities and this is a vital aspect in this investigation to identify only the useful neutron pulses and reject the gamma-ray pulses. The gamma-ray pulses are nevertheless vital for characterizing the timing of the system by looking at photo-fission events as well as the prompt gamma rays emitted by the induced fission events in the fission chamber.