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

TL;DR

This paper reanalyzes reactor antineutrino spectra using new measurements of beta spectra ratios from uranium isotopes, revealing discrepancies with previous data and providing updated predictions consistent with recent experiments.

Contribution

It introduces new relative measurements of beta spectra ratios from $^{235}$U and $^{239}$Pu, leading to revised antineutrino spectrum predictions and cross section ratios.

Findings

Observed a 1.054±0.002 excess in ILL beta spectra ratio

Reevaluated inverse beta decay cross section ratio as 1.45±0.03

New predictions align with Daya Bay and STEREO results

Abstract

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 $^{235}$U and $^{239}$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 $1.054\pm0.002$. We find a value of the ratio between inverse beta decay cross section per fission for $^{235}$U and $^{239}$Pu: $(^5\sigma_f/^9\sigma_f)_{KI} = 1.45 \pm 0.03$, and then we reevaluate the converted antineutrino spectra for $^{235}$U and $^{238}$U. We conclude that the new predictions are consistent with the results of Daya Bay and STEREO experiments.