High-precision prompt-γ-ray spectral data from the reaction 241Pu(nth, f)

In this paper we present results from the first high-precision prompt-gamma-ray spectral measurements from the reaction Pu-241(n(th), 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 gamma rays with three cerium-doped LaBr3 (two 5.08 cm x 5.08 cm and one 7.62 cm x 7.62 cm) and one CeBr3 (5.08 cm x 5.08 cm) scintillation detectors, which all exhibit excellent timing and good energy resolution. The average gamma-ray multiplicity was determined to be (nu) over bar (gamma) = (8.21 +/- 0.09) per fission, the average energy to be epsilon(gamma) = (0.78 +/- 0.01) MeV, and the total energy to be E-gamma,E-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 gamma energy is modestly higher than the one in the present evaluated nuclear data files, we suspect that the underestimation of the prompt-gamma heating in nuclear reactors is due to fast-neutron-induced fission on U-238 or rather from fission induced by gamma rays from neutron capture in the construction material.