Neutron-induced 235U fission spectrum measurements using liquid organic scintillation detectors

摘要

Measurements have been performed at Los Alamos Neutron Science Center to acquire neutron fission spectranof 235U in the energy range between 0.5 and 10 MeV. These new data complement the currently availablenexperimental data, which are not well known in the energy range below 1 and above 5 MeV. Organic liquidnscintillation detectors (EJ-309s) were used together with a digital data-acquisition system. The EJ-309 detectorsnshow excellent pulse shape discrimination capabilities and this is vital for identifying only neutron pulses andnrejecting γ -ray pulses. The measurement data show the dependence of average fission neutron energy as anfunction of the inducing neutron energy. The data agree well with previously published measurements and Wattnspectra fits for energies up to tens of MeV. At high fission-inducing neutron energies the spectrum deviates fromnWatt-spectra fits. The increased energy deposited in higher energy neutron-induced fissions does not significantlynincrease emitted fission neutron energies for up to 10 MeV. A significant decrease in neutron energy aroundnsecond-chance fission cannot be observed beyond the current measurement uncertainties.