Time-dependent quadrupole interactions in ¹²⁹I

$\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ time-differential directional correlation studies have been carried out on the $\frac{5}{{2}^{+}}$ (459.6 keV) $\frac{5}{{2}^{+}}$ (27.8 keV) $\frac{7}{{2}^{+}}$ cascade in $^{129}\mathrm{I}$ using a $^{129}\mathrm{Te}^{m+g}$ source in $4N$ HCl. The measurements reveal time-dependent electric quadrupole perturbation of the correlation. From the plot of ${A}_{2}(\overline{t})$ vs $\overline{t}$ (finite time resolution corrected), the obtained values of the relaxation parameter ${\ensuremath{\lambda}}_{2}^{\mathrm{el}}$ and the unperturbed ${A}_{2}(0)$ coefficient (solid angle corrected) are (0.21\ifmmode\pm\else\textpm\fi{}0.01) \ifmmode\times\else\texttimes\fi{} ${10}^{9}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ and -(0.068\ifmmode\pm\else\textpm\fi{}0.002), respectively. The observed ${\ensuremath{\lambda}}_{2}^{\mathrm{el}}$ is consistent with that deduced from the theory of Abragam and Pound.