Prompt gamma-ray spectra were measured for the spontaneous fission of 240,242Pu and the neutron-induced fission of 239,241Pu with incident neutron energies ranging from thermal to about 100 keV. Measurements were made using the Detector for Advanced Neutron Capture Experiments (DANCE) array in coincidence with the detection of fission fragments using a parallel-plate avalanche counter. Comparison of the unfolded prompt fission gamma-ray spectrum (PFGS) between spontaneous and neutron-induced fission reactions is shown in the figure below. The PFGS can be reproduced reasonably well by a Monte Carlo Hauser-Feshbach statistical model for the neutron-induced fission channel but not for the spontaneous fission channel. However, this entrance-channel dependence of the prompt fission gamma-ray emission can be described qualitatively by the model due to the very different fission-fragment mass distributions and a lower average fragment spin for spontaneous fission. The description of measurements and the discussion of results are presented.
This work benefitted from the use of the LANSCE accelerator facility and was performed under the auspices of the US Department of Energy by Lawrence Livermore National Security, LLC, under contract No. DE-AC52-07NA27344 and by Los Alamos National Security, LLC, under Contract No. DE-AC52-06NA25396. Funding is acknowledged from the US DOE/NNSA Office of Defense Nuclear Nonproliferation R&D and US DOE/SC Office of Nuclear Physics.