MICRO-PIXE AND MILLI-PIXE ANALYSIS AT 40 MEV - WHY, HOW AND WHEN

Low-energy protons have difficulty in ionizing the K-shells of heavier elements, and elemental identification depends upon the analysis of L- rather than K X-ray spectra. Higher-energy protons excite K X-rays with suitable efficiency for easy detection. 40 MeV protons are ideal as probes of the K-shell for medium to heavy elements and are particularly valuable in studies of the rare-earth region and above. Microbeams are now available and invaluable in certain situations. Microprobes with spot sizes below 10 μm are not always as useful as might be believed. Submicron spots, on the other hand, are opening up new fields of study. Why is PIXE analysis at higher energies valuable and an essential complement to low-energy analysis? How do you produce a high-energy microbeam; how does it scan, and when should you use it in preference to an alternative millibeam of the same energy? These questions and others relating to the design of custom-made proton microprobes are addressed in this paper. New experimental data are presented, illustrating applications to biological, material and mineralogical analysis. © 1990.