Relativistic ionisation cross sections for use in microanalysis

The determination of quantitative information about specimens from elemental maps as well as from data of electron energy loss spectroscopy (EELS) or energy dispersive X-ray analysis (EDX) microanalysis necessitates an accurate knowledge of the appropriate cross-sections. Though there is a growing number of microscopes operating at high acceleration voltages, the influence of relativistic effects such as the magnetic interaction and retardation on the scattering process has been neglected in calculations of cross-sections up to now. In this paper we shall outline the calculation of cross-sections for EELS and EDX based on a fully relativistic concept. The calculations were carried out for the case of K-shell ionisation, based on a hydrogenic model, and in dipole approximation, valid for arbitrary core shells. The results are finally compared with experimental data, which have been obtained with the JEOL-ARM1000 microscope in Kyoto.