Differential PIXE Analysis of Layered Automobile Paint

Analysis of multi-layered samples is both time consuming and destructive; the layers must be mechanically separated and chemically dissolved, destroying the sample in the process. Particle Induced X-ray Emission (PIXE) uses a particle accelerator for non-destructive chemical composition analysis. Differential PIXE uses varying beam energies to penetrate different depths into the sample. In multi-layered samples, the different energies produce x-rays from only the layers which the beam passes through. A target element unique to each layer is used to tell the layer in which the beam stops at varying energies. Concentrations are obtained from the spectra using the peak fitting program GeoPIXE, which is particularly useful because it has multi-layered fitting capabilities. By adjusting the thickness of a layer until the target element concentrations are consistent across all energies, it is possible to approximate the thickness of that layer without taking it apart. With this method, at least two layer thicknesses in the five layer sample can be determined