Can decay heat measurements tell us something about the Reactor Antineutrino Anomaly?

TL;DR

This study investigates whether decay heat measurements from historical fission experiments can shed light on the Reactor Antineutrino Anomaly, highlighting discrepancies in spectral ratios and emphasizing the need for new high-precision measurements.

Contribution

The paper demonstrates how existing decay heat data can be used to analyze the Reactor Antineutrino Anomaly and identifies the necessity for new experimental measurements.

Findings

Spectral ratios for uranium and plutonium isotopes align with recent lower trend reports.

Discrepancies exist between historical spectral ratios and older measurements from the 1980s.

A new experimental campaign with advanced spectrometry is recommended.

Abstract

Measurements of the decay energy released as a function of time following the thermal neutron induced fission on $^{235}$U and $^{239,241}$Pu were performed in the 1970s at Oak Ridge National Laboratory with the purpose of quantifying possible Loss Of Coolant Accident scenarios. This decay energy, known in technical parlance as decay heat, is mainly composed of two terms, that of the electrons produced together with antineutrinos in the beta-minus decay of the neutron-rich fission products, and that of the gammas produced in the subsequent decay of excited nuclear levels. In this work we study if this extensive set of decay heat measurements can be used to assess the Reactor Antineutrino Anomaly, that is, the approximately 5\% deficit of electron antineutrinos produced by nuclear reactors, first deduced by Mention and collaborators in 2011, and observed by the major reactor antineutrino experiments near nuclear power plants since. With the assistance of nuclear databases, we are able to obtain the ratio of electron spectra under equilibrium conditions for $^{235}$U to $^{239}$Pu, in better agreement with the lower trend recently reported by Kopeikin and collaborators, as well as those for $^{235}$U to $^{241}$Pu and $^{241}$Pu to $^{239}$Pu, which do not agree well with those measured at the Insitut Laue-Langevin in the 1980s. We conclude that a new experimental campaign is needed to measure the electron spectra utilizing a high-resolution and signal-to-noise-ratio electron spectrometer and a highly precise fission normalization procedure.