Quantitative PIXE analysis using a scanning proton microbeam

PIXE analysis is often quoted as being simple, fast, accurate and multielemental. In practice, however, especially if a wide range of samples is analysed, the measurements are adversely affected by uncertainty about the sample matrix composition, thickness and homogeneity. This is particularly true for thick samples, where major corrections to the X-ray yield can depend on knowledge of the chemical composition of the specimen. This can often be circumvented by techniques such as determination of bulk composition by other methods, or comparison with standards, but all these additional processes add to the analysis time and complexity. In addition, it is necessary to assume that the sample composition is uniform over the full area of the beam spot, not necessarily true even for carefully homogenised materials. This paper describes how the use of a scanning proton microbeam (SPM) with simultaneous PIXE, backscattered particle spectroscopy and secondary electron detection can enhance the accuracy of PIXE analysis by allowing the selection of a uniform region of the sample and the determination of the matrix composition. System calibration procedures are described and examples of analyses of standard reference materials and experimental samples are presented.