Surface diffusion from a needle source including the effect of volume diffusion into the bulk

The problem of determining the quantity of diffusant to be found on and beneath the surface of a solid at any radial distance from a cylindrical source of constant strength on the surface has been solved using a Laplace transform technique. The movement of diffusant from the surface into the bulk through volume diffusion was taken into account. The integrals in the solution were evaluated numerically for a wide range of experimentally realizable conditions and the results given in a table. Experimental data can be analyzed with the help of this table to yield the product of the surface diffusion coefficient and the thickness of the surface layer. It is shown that, in general, these two quantities cannot be determined separately from data obtained in a conventional experiment because the amount of diffusant in the surface layer is usually only a small fraction of the total measured at any point.