Modernizing the Fission Basis

A recent Fission Product Review Panel study has identified important issues associated with the possible neutron energy dependence of the fission product isotope $^{147}$Nd. As a result, we initiated a program at TUNL to obtain high-precision and self-consistent data for the energy dependence of fission product yields in the 1 to 15 MeV energy range. Three dual fission ionization chambers dedicated to $^{235}$U, $^{238}$U, and $^{239}$Pu thick target foils and thin monitor foils, respectively, were exposed to neutron beams produced via the reactions $^{2}$H(d,n)$^{3}$He and $^{3}$H(d,n)$^{4}$He. After irradiation, the characteristic $\gamma $ rays from specific fission products were recorded over a period of many weeks using HPGe detectors in a low-background environment. Results for the yield of seven fission isotopes obtained at 4.6, 9.0 and 14.8 MeV are reported.