Energy dependence of fission product yields in the second-chance fission region

An extensive dataset of cumulative fission product yields has been generated under a joint collaboration between Los Alamos National Laboratory (LANL), Lawrence Livermore National Laboratory (LLNL), and the Triangle Universities Nuclear Laboratory (TUNL). The energy dependence of the cumulative yield for a select number of high -yield fission products has been measured using quasimonoenergetic neutrons with energies between 5.5 and 11.0 MeV. This is in addition to previously published data covering 0.5-4.5 and 14.8 MeV. The absolute number of fissions was determined during the irradiation period using dual -fission ionization chambers, and the fission products were measured postactivation by whole target gamma -ray spectroscopy. This paper presents the absolute cumulative fission product yields as a function of incident neutron energy from the neutron -induced fission of 235U, 238U, and 239Pu isotopes at four incident energies in the second -chance fission region and compares them with existing literature values. Corrections relevant to this collaboration's previously published data are also discussed.