The Energy Dependence of Fission Product Yields

Under a collaboration between Los Alamos National Laboratory, Lawrence Livermore National Laboratory and the Triangle Universities Nuclear Laboratory, a set of absolute cumulative fission product yield measurements has been performed. The energy dependence of cumulative fission product yields (FPY) have been measured using quasi-mono-energetic neutrons for three actinide targets, ²³⁵U, ²³⁸U and ²³⁹Pu, between 0.5 and 14.8 MeV. The FPYs were measured by a combination of direct fission counting using specially designed dual-fission chambers and γ-ray spectroscopy. Each dual-fission chamber is a back-to-back ionization chamber encasing an activation target in the center with thin deposits of the same target isotope in each chamber. This method allows for the direct measurement of the total number of fissions in the activation target with no reference to the fission cross-section, thereby reducing the uncertainties. Data will be presented showing fission yield results for the energy range covering 6.5 - 11 MeV, fully covering the second chance fission region. Previous data from this work for 0.5 - 5.5 MeV and 14.8 MeV, that has already been published, will now be combined with the newly finalized data from the second chance region. This will provide a complete picture on the energy dependence of the cumulative fission product yields for more than a dozen peak yield fission products from the 3 major actinides.