Tracer Diffusion in a Chemical Concentration Gradient in Silver-Cadmium

Measurements have been made on seven Ag-$\alpha \mathrm{AgCd}$ diffusion couples of the diffusion of a layer of radioactive tracer atoms (either ${\mathrm{Ag}}^{110}$ or ${\mathrm{Cd}}^{109}$) located originally at the Ag-AgCd interface. It was found that the center of gravity of the layer of tracer atoms shifted from its original position, marked by tungsten wires. The shapes of the tracer profiles for ${\mathrm{Ag}}^{110}$ were quite different from those for ${\mathrm{Cd}}^{109}$. However, for both silver and cadmium tracer, the center of gravity moved toward the cadmium-rich region.