High-precision prompt- γ -ray spectral data from the reaction Pu241 ( nth , f )

In this paper we present results from the first high-precision prompt-γ-ray spectral measurements from the reaction Pu241(nth, f). Apart from one recent experiment, no data are reported in the literature for this fissioning system, which motivated a new dedicated experiment. We have measured prompt-fission γ rays with three cerium-doped LaBr3 (two 5.08cm×5.08 cm and one 7.62cm×7.62 cm) and one CeBr3 (5.08cm×5.08 cm) scintillation detectors, which all exhibit excellent timing and good energy resolution. The average γ-ray multiplicity was determined to be ν¯γ=(8.21±0.09) per fission, the average energy to be εγ=(0.78±0.01) MeV, and the total energy to be Eγ,tot=(6.41±0.06) MeV as the weighted average from all detectors. Since the results from all detectors are in excellent agreement, and the total released γ energy is modestly higher than the one in the present evaluated nuclear data files, we suspect that the underestimation of the prompt-γ heating in nuclear reactors is due to fast-neutron-induced fission on U238 or rather from fission induced by γ rays from neutron capture in the construction material.