A model for the confocal volume of 3D micro X-ray fluorescence spectrometer

The newest development in Micro X-Ray Fluorescence Analysis (micro-XRF) is the expansion of its capabilities to depth resolution using a confocal setup with X-ray optics. While the usefulness of this 3D micro-XRF method has already been shown for a number of applications, reliable quantification procedures still have to be developed. In this paper, we present expressions for the primary fluorescence intensity of various types of 3D micro-XRF experiments based on the fundamental parameter approach. A major constituent of these equations is the description of the confocal volume defined by the X-ray optics used. The model provides analytical expressions for the sensitivity of the 3D micro-XRF spectrometer, which is the characteristic quantity. It opens up the way for an experimental characterization of the spectrometer and for a general quantification of 3D micro-XRF measurements. First experimental evidence is presented for the validity of relations derived. Furthermore, distinct features of 3D micro-XRF measurements in comparison to ordinary XRF measurements are discussed