Study of the dependence of 198Au half-life on source geometry

TL;DR

This study investigates whether the half-life of gold-198 depends on the source's shape, motivated by claims that solar neutrinos might influence nuclear decay rates, and finds no significant dependence within experimental uncertainty.

Contribution

It provides experimental evidence that gold-198's half-life is independent of source geometry, constraining the influence of solar neutrinos on nuclear decay rates.

Findings

Half-life ratio of foil to sphere is 0.999 ± 0.002.

Experiment increased neutrino flux to test decay rate dependence.

Results set limits on solar neutrino effects on nuclear decay.

Abstract

We report the results of an experiment to determine whether the half-life of \Au{198} depends on the shape of the source. This study was motivated by recent suggestions that nuclear decay rates may be affected by solar activity, perhaps arising from solar neutrinos. If this were the case then the $\beta$-decay rates, or half-lives, of a thin foil sample and a spherical sample of gold of the same mass and activity could be different. We find for \Au{198}, $(T_{1/2})_{\rm foil}/(T_{1/2})_{\rm sphere} = 0.999 \pm 0.002$, where $T_{1/2}$ is the mean half-life. The maximum neutrino flux at the sample in our experiments was several times greater than the flux of solar neutrinos at the surface of the Earth. We show that this increase in flux leads to a significant improvement in the limits that can be inferred on a possible solar contribution to nuclear decays.