  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.
