monochromatising x-ray guides

Monochromatizing x-ray guides are combinations of planar or cylindrical capillaries with graphite crystals. Monochromatization is achieved by means of highly orientated pyrolytic graphite crystals (HOPG) with a mosaic structure having a half width of the rocking curve of about 4 mrad. The radiation from the X-ray source illuminates the HOPG crystal either directly or is transported by a capillary. A second capillary is used to transport the monochromatized radiation to the sample with minimum losses. The most important point in these schemes is the match of the angle of total external reflection of the capillary material and the half width of the rocking curve of the crystal. A considerable intensity gain is achieved by careful optimization of the geometry of these devices.

The typical performance of a monochromatizing x-ray guide with a single capillary at the exit (MONO-FOX) may be characterized by the following measurement results.
Measurement conditions:

Source: x-ray tube with Cu or Mo anodes, spot size - 0.4 x 0.8 mm²
Capillary length L = 135 mm, capillary diameter D_c = 0.5 mm
Geometry: distances source - MONO-FOX = 55 mm, source - goniometer = 350 mm, goniometer - detector = 330 mm (slit width 0.01 mm)

The measurements were compared with those carried out with a HUBER flat monochromator 151 (HOPG crystal without x-ray guides, pinhole 0.5 mm) at similar geometric conditions with a collimator length of 105 mm.

Application:

- High sensitivity diffractometry
- Structure analysis, texture and stress analysis
- High sensitivity XRF analysis