X-ray guide tube for diffraction experiments

For diffraction experiments with an extremely small crystal or with very long distance from X-ray source to detecting instrument, the use of an `X-ray guide tube' (XGT) is proposed on the basis of a simple consideration and experiment with a Pyrex-glass tube. X-ray intensities through an XGT of glass and also through a pin hole were measured as a function of photon energy and compared to derive the gain by use of XGT. At wavelengths between Cu Kα and Mo Kα radiations, the observed gain in brightness is about thirty to twenty for the present setup, corresponding to about 50 to 80% of the maximum possible gain calculated on the assumption that the reflectivity of X-ray total external reflection is 1.0.