Test of Nuclear Decay Rate Variation due to an Antineutrino Flux

TL;DR

This study investigates whether antineutrino flux from a reactor affects nuclear decay rates, finding no measurable variation and setting more sensitive upper limits than previous experiments.

Contribution

The paper provides the first high-sensitivity measurements of decay rate variations due to antineutrino flux, establishing more stringent upper limits on possible interactions.

Findings

No detectable decay rate variation observed.

Set upper limits on decay-antin neutrino cross sections.

Improved sensitivity by a factor of 10,000 over past experiments.

Abstract

Unexplained variations of the decay rate for weak interaction decays such as $\beta^{\pm}$-decay, electron capture, as well as strong interaction $\alpha$-decay have been reported. Some researcher interpreted these variations as caused by an unexplained fundamental interaction. The purpose of the paper is to review decay rate parameter variations experiments and place them into a common comparable context and to make decay parameter measurements at the level of 10$^{-5}$ in the presences of an antineutrino flux, $\sim 3 \times10^{12}$ $\overline{\nu} \, cm^{-2} \, sec^{-1}$, 6.5 meters from the High Flux Isotope Reactor(HFIR) reactor core having an on-off cycle time of $\sim$30 days. Two weak interaction decays, one via electron capture and the other via $\beta^-$ decay were selected because the final state and the time reverse state each contain a neutrino and anti-neutrino, covering arguments that the anti-neutrino flux may interact differently or not at all in one of the cases. The experiment searched for variation of the $^{54}_{25}$Mn, e$^-$ capture and $^{137}_{~55}$Cs, $\beta^-$ decay rate parameters. The measured variation in the decay rate parameters are found to be $\delta \lambda/ \lambda = (0.034\pm 1.38)\times 10^{-5}$ for $^{54}_{25}$Mn and $\delta \lambda/ \lambda = (0.67\pm 1.56)\times 10^{-5}$ for $^{137}_{~55}$Cs. These results are consistent with no measurable decay rate parameter variation due to an antineutrino flux, yielding a $68\%$ confidence level upper limit sensitivity for $^{54}_{25}$Mn, $\delta \lambda/ \lambda \leq 1.31\times10^{-5}$ or $\sigma \leq 1.29\times10^{-25}\,cm^{2}$ in cross section and for $^{137}_{~55}$Cs, $\delta \lambda/ \lambda \leq 2.23\times10^{-5}$ or $\sigma \leq 5.69\times10^{-27}\,cm^{2}$. These null or no observable effect measurements places cross-section upper limits $\sim 10^{4}$ times more sensitive than past experiments.