intermediate-energy neutron-induced fission of uranium: Product yields and isomer studies

An experimental program for studying the properties of fission induced by intermediate energy neutrons has been started at the Los Alamos Neutron Science Center (LANSCE). Experiments using the GEANIE high-resolution gamma-ray spectrometer were performed to extract excitation functions for fission products obtained from a ²³⁸U target. Results of the singles data for xenon isotopes are presented to illustrate the method, and show that the rotational ground-state-band transitions are suited for the extraction of production cross-sections of even-even fission products. Coincidence data are analyzed to produce isotopic distributions of barium for three neutron energy groups. Also, an example of the evolution with incident neutron energy of the relative intensities of coincident transitions is compared to data of spontaneous fission. The result may indicate the persistence in the fission products (prior to gamma-ray decay) of residual angular momentum from the compound nucleus at neutron energies above 50 MeV.