Localization of impurity atoms in garnet cystals by the double-channel X-ray standing-wave method

A double-channel X-ray standing-wave technique has been suggested. It reduces to simultaneous recording of photoelectrons and fluorescence radiation coming from a crystal under the conditions of X-ray diffraction. The use of a coincidence circuit allows one to obtain fluorescence radiation from small depths of electron escape and to eliminate distortions of fluorescence angular dependence owing to X-ray extinction. The double-channel X-ray standing-wave method was used to record the fluorescence yield curves free of extinction distortions from gadolinium and gallium atoms occupying different lattice positions in gallium-gadolinium garnet. The positions of impurity terbium atoms in yttrium-aluminium garnet have been determined. The influence of indirect excitation of a secondary radiation on the angular yield curves obtained has also been considered.