Charged particle-induced X-ray emission (PIXE): applications

The purpose of this article is to provide the practical information needed to implement the PIXE analysis technique, the theoretical foundations of which have already been explained (article In principle, it's easy to use, since all that's required is to place a sample in the beam, without any special preparation apart from vacuum bagging, to obtain a qualitative composition in just a few minutes. In reality, to obtain precise quantitative results and optimize sensitivity, a number of experimental precautions need to be taken with regard to the shape of the sample (solid, powder deposited in a thin layer or sintered, dehydrated or pre-concentrated liquid), its physical characteristics (conductivity, surface state, etc.) and, finally, the type of beam used (ion, energy, flux) as well as the analysis geometry. In recent years, the vacuum constraint has even been lifted, as air-extracted beams are now available, making it possible, among other things, to analyze very bulky objects at atmospheric pressure, particularly in the field of art. All these aspects will be developed in the "Instrumentation" section.

The next chapter will focus on the processing required to express concentrations from experimental results. Current codes for deconvolving X-ray fluorescence spectra can be used to resolve most thin-target situations, and to obtain absolute quantitative results without using standard samples. X-ray emission yields are well known, as is the response of semiconductor detectors. These codes also make it possible to work with thick targets, where matrix effects in the form of projectile slowdown and attenuation of emitted X-rays come into play. These phenomena can be modelled quite simply, and thick-target analysis is increasingly used in cases where no alternative is possible.

Thanks to its multi-elemental nature, the microbeam method can map more than a dozen elements in the same analysis, with scan dimensions ranging from 20 µm to 2 mm and optimum spatial resolution of the order of a few hundred nanometers. The use of such beamlines is described in this treatise (article [P 2 563] ).

Some examples of applications in disciplines as diverse as life and environmental sciences, earth sciences, materials sciences, archaeometry... are presented in the last part of the article.

The theoretical underpinnings of the method were presented in the article .