Validation of the RBS analysis for colloid migration through a rough granite surface

Colloids permeation into microfractures of crystalline rocks has been recently studied by RBS techniques, in order to determine the colloid diffusion coefficients in a laboratory time span. The measure of concentration profiles at the micrometer scale can be performed by RBS technique, however fakes due to surface heterogeneity and roughness can affect the spectra interpretation. In order to validate the technique in the particular case of colloid migration in granite, a study of the concentration profiles of 40 and 100 nm gold colloids is presented in this work. Contact time dependence of the RBS gold signal and experiments performed at different incident angles suggest that the observed signal is actually due to Au depth profiles and not to roughness effects. Furthermore, Monte Carlo simulations have been developed to differentiate the effects of the surface roughness and particle deposition on the surface, from colloids permeation