Reevaluating reactor antineutrino spectra with new measurements of the ratio between ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$ $\beta$ spectra

We report a reanalysis of the reactor antineutrino energy spectra based on the new relative measurements of the ratio $R={{}^{e}S}_5/{{}^{e}S}_9$ between cumulative $\beta$ spectra from ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$, performed at a research reactor in National Research Centre Kurchatov Institute (KI). A discrepancy with the $\beta$ spectra measured at Institut Laue-Langevin (ILL) was observed, indicating a steady excess of the ILL ratio by the factor of $1.054\pm 0.002$. We find a value of the ratio between inverse beta decay cross section per fission for ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$: ${(}^5{\sigma }_f{/}^9{\sigma }_f{)}_{KI}=1.45\pm 0.03$, and then we reevaluate the converted antineutrino spectra for ${}^{235}\mathrm{U}$ and ${}^{238}\mathrm{U}$. We conclude that the new predictions are consistent with the results of Daya Bay and STEREO experiments.

Figure 1

Ratios $R={{}^{e}S}_5/{{}^{e}S}_9$ between cumulative $\beta$ spectra from ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$ from ILL data [11] (the upper curve, blue) and KI data [10] (the lower curve, red). Total electron energies are given. Only statistical errors are shown.

Figure 2

Ratios $R$ between cumulative $\beta$ spectra from ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$, normalized to the KI data. Plotted ILL quantities were divided by 1.054, as explained in the text. The colored region shows KI uncertainties.