A NEW METHOD FOR ONLINE TRUE-ELEMENTAL IMAGING USING PIXE AND THE PROTON MICROPROBE

A rapid matrix transform method called Dynamic Analysis (DA) has been developed for the production of true elemental images using PIXE and the Proton Microprobe that are free of image artefacts due to continuum background and overlap with X-ray lines and detector response features (e.g. tails and escape peaks) from other elements. The method has been installed at the CSIRO and the NAC for the on-line projection of true elemental images. These on-line images are also quantitative, and only require minor off-line correction(similar to 10% typically) to obtain accurate true elemental images at major and trace element levels. Correction issues discussed include the variation of PIXE yields with sample composition across a scan area, and dead-line corrections. The method is now in routine use and enables on-line quantitative true elemental imaging at the CSIRO and the NAC using a simple procedure involving the fitting of a preliminary scan spectrum to build the DA transform matrix; spectrum fitting and matrix construction are part of the GeoPIXE software package. The method has been extensively tested using samples which display complex multi-element overlaps, the DA method successfully projecting accurate images for elements obscured by the lines of interfering elements.