Quantitative trace element imaging using PIXE and the nuclear microprobe

The X-ray spectra of pure elements, excited using MeV energy beam of proton s from the nuclear microprobe, have known spectra signatures. This makes X- ray spectra for more complex mixtures amenable to decomposition into contri butions from the component elements. By devising this procedure as a matrix operation that transforms directly from spectrum vector to elemental conce ntration vector, the decomposition can be performed very efficiently enabli ng the real-time projection of the component element signals. In the case o f a raster-scanned beam, with data that contain position information for ea ch X-ray event, this approach enables the real-time projection of component element spatial distribution images. This paper describes the matrix trans form approach called dynamic analysis (DA), which enables on-line real-time imaging of major and trace elements using proton-induced X-ray emission (P IXE). The method also provides off-line iterative yield corrections to thes e images to compensate for changing sample composition across an image area . The resulting images are quantitative in two respects: (1) they resolve t he pure element components and strongly reject interferences from other ele ments and (2) they can be directly interrogated for sample composition at e ach pixel, over areas, or along lines across the image area, with accuracy comparable to microanalytical point analysis methods. The paper describes t he DA method, presents tests, and discusses its application to quantitative major and trace element imaging in geology. (C) 2001 John Wiley & Sons. In c.