Time-Dependent Relaxation of Aligned Nuclei due to Radiation-Induced Vacancies in Solid Germanium

We observe the temperature dependence of the alignment of an isomeric state in ${}_{}{}^{73}{}_{}{}^{}\mathrm{As}$ (426 keV, ${\frac{9}{2}}^{+}$, $\tau =8\mathrm{} \mu sec$), produced by the reaction ${}_{}{}^{72}{}_{}{}^{}\mathrm{Ge}\mathrm{}(d,n)\mathrm{}{}_{}{}^{73}{}_{}{}^{}\mathrm{As}$ in solid Ge. The relaxation process can be interpreted with a diffusion-controlled time-dependent quadrupole interaction due to radiation-induced lattice damage. A diffusion energy of $E=1.3\mathrm{}\pm 0.2$ eV is assigned to the activation energy for excess vacancy diffusion. This result yields, for the first time, quantitative insight into relaxation mechanisms associated with radiation damage in solids, which may occur when implantation techniques and nuclear reactions are employed.