Energy Dependence of Fission Product Yields*

Under a joint collaboration between LANL-LLNL-TUNL, a consistent set of absolute energy dependent fission product yield measurements has been performed. For ²³⁵U, ²³⁸U and ²³⁹Pu, between 0.5 and 14.8 MeV, the energy dependence of a select number of cumulative fission product yields (FPY) have been measured using quasi-monoenergetic neutron beams at the Triangle Universities Nuclear Laboratory (TUNL). The FPYs were measured by a combination of fission counting using specially designed dual-fission chambers and γ-ray counting. 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, thus reducing uncertainties. Reported are absolute cumulative fission product yields for incident neutron energies of 0.5 - 14.8 MeV in nearly 1 MeV steps. New data in the second chance fission region of 5.5 – 11 MeV have recently been published.