Surface analysis of corroded XV–XVI century copper coins by μ-XRF and μ-PIXE/μ-EBS self-consistent analysis

Particle Induced X-ray Emission (PIXE) and X-ray Fluorescence (XRF) are nowadays routinely used for analysing historical coins. However, its characterization, especially in the presence of a superficial chemically altered layer (corrosion), is difficult due to its layered structure which cannot be probed using these two techniques in the general case. Elastic backscattering (both Rutherford and non-Rutherford) spectrometry is commonly used to determine depth profiles but by its own it is insufficient to unveil these complex structures. Using a PIXE detector and a particle detector recording simultaneously it is possible to perform a self-consistent analysis to obtain results about concentration variation of different elements along depth. In the present work this method was tested for two Portuguese centenary copper-based coins, and XRF was used to complement PIXE information. It is shown that elemental depth profiles with the evaluation of the superficial altered layer can be clearly solved providing relevant results about corrosion extension and composition.