Prompt-fission γ -ray spectral characteristics from Pu239(nth,f)

Abstract

In this paper we present new results for prompt fission $\ensuremath{\gamma}$-ray spectral characteristics from the thermal neutron induced fission of $^{240}\mathrm{Pu}^{*}$. The measured spectra were unfolded by using the detectors' response functions, simulated with geant4. We obtained in average per fission a $\ensuremath{\gamma}$-ray multiplicity ${\overline{M}}_{\ensuremath{\gamma}}=(7.35\ifmmode\pm\else\textpm\fi{}0.12)$, a mean photon energy ${\overline{\ensuremath{\epsilon}}}_{\ensuremath{\gamma}}=(0.85\ifmmode\pm\else\textpm\fi{}0.02)$ MeV, and an average total energy released in fission ${\overline{E}}_{\ensuremath{\gamma},\mathrm{tot}}=(6.27\ifmmode\pm\else\textpm\fi{}0.11)$ MeV. Our results are in good agreement with historical data measured in the 1970s by Verbinski et al. and results from recent calculations in the framework of Monte Carlo Hauser--Feshbach models. Our measured average total energy is slightly smaller than the one deduced previously and present in evaluated data. From this we conclude that the $^{239}\mathrm{Pu}({n}_{\mathrm{th}},f)$ reaction may be ruled out as possible source of $\ensuremath{\gamma}$ heating underestimation, when compared with benchmark calculations based on existing nuclear data.