A SIMPLE-MODEL FOR OPTIMIZATION OF CONICAL CAPILLARIES IN XRF ANALYSIS

The method of total reflection in conical glass capillaries has been used for several decades for obtaining high-intensity x-ray microbeams of small spot size. A general problem with this technique is the small critical angle, which is energy dependent. There is a certain loss of intensity if many reflections occur in the capillary. Assuming parallel monoenergetic x-rays, a simple relationship has been derived for the intensity enhancement as a function of the reflectivity of the glass and the number of reflections. The relationship was used to derive conditions for optimum intensity enhancement. Also for suboptimum conditions the relationship can be used to design entrance and exit diameters and length of the capillary. The model was also applied to a wedge-shaped slit that consists of two total reflection plates.