High-precision prompt-γ-ray spectral data from the reactionPu241(nth,f)

Abstract

In this paper we present results from the first high-precision prompt-$\gamma$-ray spectral measurements from the reaction ${}^{241}\mathrm{Pu}$($n_{\mathrm{th}}$, $f$). 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 $\mathrm{La}{\mathrm{Br}}_3$ (two $5.08\text{cm}\times 5.08$ cm and one $7.62\text{cm}\times 7.62$ cm) and one $\mathrm{Ce}{\mathrm{Br}}_3$ ($5.08\text{cm}\times 5.08$ cm) scintillation detectors, which all exhibit excellent timing and good energy resolution. The average $\gamma$-ray multiplicity was determined to be ${\overline{\nu }}_{\gamma }=(8.21\pm 0.09)$ per fission, the average energy to be ${\epsilon }_{\gamma }=(0.78\pm 0.01)$ MeV, and the total energy to be $E_{\gamma ,\text{tot}}=(6.41\pm 0.06)$ 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 ${}^{238}\mathrm{U}$ or rather from fission induced by $\gamma$ rays from neutron capture in the construction material.