Differential PIXE Analysis of Multi-layer Auto Paint
Dr. Paul DeYoung and Dr. Graham Peaslee
Differential Particle Induced X-ray Emission (DPIXE) has been successful as a technique to analyze carefully-prepared multi-layer auto paint samples in a nondestructive manner. However, the analysis of weathered samples ripped from a car in a salvage yard is more difficult. Particle Induced X-ray Emission (PIXE) involves particle beams produced by a particle accelerator to analyze the concentration of elements present in one or more layers. As the beam penetrates into the sample, characteristic x rays of various energies are emitted which correspond to different elements in the sample. DPIXE involves varying the beam energy so the beam penetrates to different depths within the sample, emitting x rays from only the layers through which the beam has passed. Quantitative analysis begins with taking measurements of the thickness of each layer. A Scanning Electron Microscope (SEM) allows us to view a cross-section of paint and measure the thickness of each layer. A careful combination of the SEM data and DPIXE data is required to obtain accurate concentrations of elements in a sophisticated peak fitting program (GeoPIXE) with calculations of energy loss as the beam penetrates to different depths and reabsorption of x rays as they travel out of the sample towards the detector. We plan to continue to refine the technique and recreate the success of the carefully prepared sample with our weathered samples.
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