  We report a comparison of the $1/T_1$ spin lattice relaxation rates (SLR) for
$^9Li$ and $^8Li$ in Pt and SrTiO$_{3}$, in order to differentiate between
magnetic and electric quadrupolar relaxation mechanisms. In Pt, the ratio of
the $1/T_{1}$ spin relaxation rates $R_{Pt}$ was found to be 6.82(29), which is
close to but less than the theoretical limit of $\sim7.68$ for pure magnetic
relaxation. In SrTiO$_{3}$ this ratio was found to be 2.7(3), which is close
but larger than the theoretical limit of $\sim2.14$ expected for pure electric
quadrupolar relaxation. These results bring new insight into the nature of the
fluctuations in the local environment of implanted $^8Li$ observed by
$\beta$-NMR.
