Fission Product Yield Measurements of ²³⁵U, ²³⁸U, and ²³⁹Pu from 2 MeV Neutron Irradiation

We report new experimental results of cumulative fission product yields (FPY) from neutron-induced fission of ²³⁵U, ²³⁸U, and ²³⁹Pu using quasi-monoenergetic neutrons at 2 MeV. Experiments were performed at the Triangle Universities Nuclear Laboratory (TUNL) employing a dual-fission chamber, with thin (10-100 µg/cm²) reference foils of similar material to a thick (100-400 mg) activation target held in the center between the two chambers. This method allows for the accurate determination of the number of fissions that occurred in the thick target without requiring knowledge of the fission cross section or neutron fluence on target. Fission products in the thick activation target were identified and quantified via high-resolution γ-ray spectroscopy using shielded 60% HPGe detectors at TUNL. Yields were measured for over 30 fission products per actinide, with uncertainties typically less than 10%. These data offer a new benchmark for fission modeling and validation of evaluated nuclear data libraries (e.g., ENDF/B-VIII.0), particularly in an energy region where experimental FPY data are sparse. Comparisons to theoretical model predictions and existing evaluations reveal notable discrepancies in the asymmetric peak and rare-earth regions. Recent FPY data has practical importance with implications for nuclear energy applications, nonproliferation, and nuclear forensics.