Transmission of X-rays From an Extended X-ray Source Through Parallel-bore Glass Capillary Waveguides: Implications for the Design of a Laboratory X-ray Microprobe

Abstract

Results are presented from a ray tracing program, used to model the transmission efficiency of parallel-bore glass capillaries configured as X-ray waveguides and coupled to X-ray tube sources of finite size. A detailed explanation of the transmission mechanisms is given in terms of regions of the source that contribute to the transmission of rays. Results (Fig. 7) predict that the highest flux is observed when the capillary is in contact with the source. As the capillary is moved away from the source, transmitted intensities first fall off, and then rise again as a larger area of the source is able to contribute rays for transmission. Intensities continue to rise with increase in the source-to-capillary distance until the point is reached where the entire area of the source can contribute to the transmission characteristics. Transmitted intensities then begin to fall off rapidly. The results indicate that transmission target tubes may have some favourable characteristics in this application and that the transmission efficiency of polycapillary (Kumakhov) lenses should not be seriously compromised, provided that the source size, in relation to source-to-lens distance, is optimised.