DIFFERENTIAL DIFFUSION OF IMPURITIES IN Li MATRICES

The diffusion of 22Na and 195Au has been investigated in solid, isotopically pure 8Li and 7Li metal. The Na tracer has been found to diffuse by about 4% faster in 8Li than in 7Li. For Au the corresponding difference was 4% at the melting point, but as much as about 15% at § Tm (°K). A formalism is given for the interpretation of diffusion experiments where the matrix isotope mass is varied. The present results for Na in Li can be plausibly explained in terms of the vacancy mechanism. For Au diffusion in Li, the interpretation appears incompatible with a simple vacancy mechanism, and the anomalous departure from the inverse root mass relationship can be connected with recently detected quantum effects in ®Li —7Li mutual diffusion.