A conical-type X-ray guide tube for diffraction experiments with small crystals

The divergence and intensity distribution of X-rays transported through a conical-type X-ray guide tube (XGT) were measured. Diverging X-rays from a point source were condensed by use of the conical-type XGT. The parallelism of X-rays through the XGT was better than that encountered for a cylindrical-type XGT proposed previously [Nakazawa (1983). J. Appl. Cryst. 16, 239–241]. The intensity of the X-ray beam around the central axis of the conical-type XGT was exceedingly high in comparison with that measured without the tube and almost uniform over a cross-sectional area 60 μm in diameter. The high intensity provides the possibility of performing diffraction experiments with crystals as small as 20 μm in diameter with a conventional X-ray diffraction system.