Modelling the transmission of X-rays through glass capillary waveguides: implications for the design of a laboratory X-ray microprobe

Abstract

New results from a ray-tracing program are presented to demonstrate the transmission of X-rays by total external reflection through glass capillaries designed for use as waveguides in laboratory X-ray microprobe instrumentation. The transmission properties of both parallel and tapered-bore capillaries have been considered. In the case of parallel-bore capillaries, results have been used to demonstrate the optimization of various experimental parameters required to maximize the intensity of the transmitted beam. In the case of tapered-bore capillaries, results have been used to understand the relatively complex transmission pattern observed at the capillary exit. For capillaries with a relatively large taper angle, an annular band structure is observed in the transmitted beam with individual components corresponding to directly transmitted rays and rays transmitted after 1, 2, 3 … reflections. These bands merge into a single profile for small observation distances from the capillary exit or for capillaries with smaller taper angles. These observations derived by computer modelling have been validated by the agreement with published experimental data for a dihedral waveguide.