No correlation between Solar flares and the decay rate of several $\beta$-decaying isotopes

TL;DR

This study investigates whether Solar flares influence the decay rates of certain isotopes and finds no significant correlation, setting strict limits on possible decay rate variations during Solar flares.

Contribution

It provides the first rigorous test for decay rate changes during Solar flares using multiple isotopes and detector setups, establishing new upper bounds on such effects.

Findings

No decay rate variation detected during September 2017 Solar flares.

Sets a 2σ upper limit of 0.044% on decay rate deviations around Solar flares.

Excludes previously claimed 0.1% decay change during December 2006 Solar flares at 4.7σ significance.

Abstract

We report on finding no correlation between the two strongest observed Solar flares in September 2017 and the decay rates of $^{60}$Co, $^{44}$Ti and $^{137}$Cs sources, which are continuously measured by two independent NaI(Tl) detector setups. We test for variations in the number of observed counts with respect to the number of expected counts over multiple periods with timescales varying from 1 to 109 hours around the Solar flare. No excess or deficit exceeds the 2$\sigma$ global significance. We set a conservative lower limit on the decay rate deviation over an 84-hour period around the two correlated Solar flares in September 2017 to $0.044\%$ with 2$\sigma$ confidence. A fractional change of $~0.1\%$ in the decay rate of $^{54}$Mn over a period of 84 hours was claimed with 7$\sigma$ significance during multiple Solar flares in December 2006. We exclude such an effect at 4.7$\sigma$ significance.