Solar Influence on Nuclear Decay Rates: Constraints from the MESSENGER Mission

TL;DR

This study analyzes Cs-137 decay data from the MESSENGER spacecraft to investigate potential correlations between nuclear decay rates and solar activity, setting limits on such influences and suggesting future improvements.

Contribution

It provides the first constraints on solar influence on Cs-137 decay rates using space-based data and proposes that future measurements could detect smaller effects.

Findings

No significant solar influence detected in Cs-137 decay rates

Estimated solar influence parameter  consistent with zero within uncertainties

Future data could improve sensitivity to potential solar effects

Abstract

We have analyzed Cs-137 decay data, obtained from a small sample onboard the MESSENGER spacecraft en route to Mercury, with the aim of setting limits on a possible correlation between nuclear decay rates and solar activity. Such a correlation has been suggested recently on the basis of data from Mn-54 decay during the solar flare of 13 December 2006, and by indications of an annual and other periodic variations in the decay rates of Si-32, Cl-36, and Ra-226. Data from five measurements of the Cs-137 count rate over a period of approximately 5.4 years have been fit to a formula which accounts for the usual exponential decrease in count rate over time, along with the addition of a theoretical solar contribution varying with MESSENGER-Sun separation. The indication of solar influence is then characterized by a non-zero value of the calculated parameter \xi, and we find \xi=(2.8+/-8.1)x10^{-3} for Cs-137. A simulation of the increased data that can hypothetically be expected following Mercury orbit insertion on 18 March 2011 suggests that the anticipated improvement in the determination of \xi could reveal a non-zero value of \xi if present at a level consistent with other data.