PAC perturbation factor for spin 5/2 nuclei subject to a rapidly fluctuating EFG¹

We report numerical computations of the PAC perturbation factor G₂(1) for spin 5/2 nuclei subject to a static EFG symmetric about the z-axis and an additional axially-symmetric EFG whose symmetry axis fluctuates randomly among the x, y, z directions. For sufficiently large fluctuation rates, the numerical results are described by the expression for the static interaction alone with the addition of relaxation terms. Results of applying this model to¹¹¹Cd TDPAC measurements on tetragonal ZrO₂ are described briefly. The model allows one to evaluate the probability that oxygen vacancies are trapped. the energy of association of vacancy-metal pairs, and the vacancy activation energy of motion.