Self-Diffusion in Solid Argon

The self-diffusion coefficient $D=D_0\exp (-\frac{Q^0}{\mathrm{RT}})$ for solid argon has been measured in thin specimens of large grain size by a tracer technique. The results, $D_0={{0.2\pm }_{0.14}}^{0.35}$ ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$ and $Q^0=3600\mathrm{}\pm 150$ cal ${\mathrm{mole}}^{-1\mathrm{}}$, are lower than those obtained in previous investigations. The value of $Q^0$ agrees reasonably well with a two-body absolute-rate calculation for vacancy migration, but not with calculations based on divacancy or interstitial mechanisms. The results suggest that vacancy diffusion takes place, and that many-body forces in solid argon are either very small, or else may satisfactorily be accounted for in an empirical two-body potential.