Ion Beam Analysis of Pigments

Abstract

We have analyzed single and multiple layer paint samples to evaluate 3 MeV external beam proton induced X-ray emission (PIXE) for elemental analysis of inorganic pigments. The results are compared to those from energy dispersive electron microprobe analysis and Rutherford Backscattering Spectrometry (RBS). The advantage of PIXE is that the protons' penetration depth of 100 microns is more than 25 times greater than that of 20 keV electrons and 10 times greater than 3 MeV alpha particles, thus allowing analysis of relatively thick samples of up to 100 microns. The proton beam is passed into the atmosphere (external to the vacuum system) through a thin polymer film, and the beam area on target is 1 mmz. Electron microprobe and RBS require vacuum compatible samples; therefore, the pigments were painted on silicon wafers. Calibration was obtained from metallic thin-film samples of known thickness. The cross calibration of the three analytical techniques allowed evaluation of external PIXE analysis of paint films. We suggest that this nondestructive method is suitable for elemental analysis of drawings and paintings provided that further studies indicate no long term damage is caused.