Rutherford Backscattering Spectrometry of Lead-Iron Diffusion

Accurate constraints of the diffusion closure temperature in radioisotope thermal-chronometers of early Solar System allow for greater accuracy in the dating of rocky bodies. These closure temperatures can be estimated based on the composition and geometry of the body, along with information about the diffusion coefficient and activation energy of the specific radioisotopes inside the body. Thin film diffusion experiments were performed on nine samples of pure iron pellets coated with 100nm of lead. These samples were subjected to heating at either 600°C for up to ten days, or 750°C for up to twenty-three hours, allowing for sufficient diffusion of the coating into the medium. The diffused samples were analysed at the University of Albany Ion Beam Laboratory using Rutherford Backscattering spectrometry (RBS). RBS spectra were processed using SIMNRA, an ion beam analysis program for Windows, to generate concentration profiles of the diffused lead. These profiles were fit to the thin-film solution to Fick's Second Law linear diffusion equation, returning diffusion coefficients for Pb in Fe 600°C and 750°C. Our results give an activation energy of 364±53 kJ/mol, within reason of expected values for diffusion in metals. This information can be used in tandem with other work in this ongoing project.