Effect of Coster-Kronig Transitions on X-Ray Generation

Abstract

The first of the physical processes leading to x-ray generation is the ionization of an atom in one of the inner shells, caused by energetic particles (e.g., electrons, protons, or x rays). Different radiative and nonradiative transitions present concurrent channels for the atom to return to the ground state. As is known, the most common nonradiative transitions are the Auger transitions, in which the vacancy of the singly ionized atom is transferred from one of the inner shells to another and the difference in the energy is released by the emission of one of the outer shell electrons. A special case of these two-electron processes is that of the Coster-Kronig transitions in which the two inner-shell electrons are situated on two different subshells of the same inner shell (e.g., L 1 and L 3). Although these transitions do not produce x rays directly, they change the distribution of the primary vacancies between the different subshells of the same shell. As a consequence they alter the absolute intensity of the analytical line, the relative intensities of the different lines in the same line family and the depth distribution of the generated x rays. The magnitude of the change caused is a function of the atomic number and of the excitation. Although proton-induced x-ray emission (PIXE) and x-ray fluorescence analysis (XRF) are also affected in a similar way and some of these effects can be examined in the transmission electron microscope (TEM) too, we concentrate on the effects experienced in electron probe x-ray microanalysis of bulk samples (i.e., the microprobe).