Self-Absorption corrections in Fluorescence EXAFS

Abstract

Variation of the absorption properties as a function of energy across, or near, an absorption edge is known as EXAFS (Extended X-ray Absorption Fine Structure). This technique implies scanning over an absorptionedge and simultaneously record the (fluorescent in this case) signal by a suitable detector. This signal contains, among other things, information of the local chemical coordination (interatomic distances etc.) of the compound observed. It is a well-known and much used technique. However, one issue which has not been considered well enough, is the question of influence by the sample geometry. As a first approximation one always assumes a sample of ”infinite size”, or only one finite thickness parameter. The department’s research group, has been working with improving this, by taking into consideration the sample geometry in terms of a cylinder or a sphere. The theory dealing with these geometries has been established. There was also collected absorption coefficient’s data sets for this, using copper sulphate as the reference sample. The purpose of the work is to analyze the data sets and perform the developed self absorption corrections and evaluate whether it is possible to establish a new correction tool. The data processing and the execution of the correction models confirm the dependency of the self-absorption effect on parameters such as concentration and thickness (by inner radius) of the sample, and a good agreement between the first order approximation and complete numerically evaluated corrections for both spherical and cylindrical cases.