ISOTOPE EFFECT FOR DIFFUSION OF GOLD IN LEAD INDIUM ALLOYS

The effect of isotopic mass on the diffusion of Au in Pb-In alloys has been studied over a composition range of 0-2.0 at. % indium. It has b een found that the strength of the isotope effect E is 0.18 +/- 0.03 f or pure lead with negligible temperature dependence. This result is co nsistent with other isotope effect measurements for ''fast diffusers'' in polyvalent materials. The isotope effect increases with increasing In concentration, reaching 0.4 +/- 0.04 with 2.0 at.% In added, and t he variation with temperature is again less than the experimental erro r. Since the anticipated value of the isotope mass is near unity for a simple interstitial mechanism for pure lead, it is clear that the dif fusion mechanism for Au in Pb-In alloys cannot be accounted for by thi s mechanism.