A theoretical analysis of the parametric X-radiation (PXR) produced by the
nonrelativistic electrons in an X-ray tube with a monocrystalline anode is
presented. It is shown that PXR can be considered as a source of quasi-mono
chromatic X-radiation for laboratory diffraction experiments. The intensity
of the PXR is comparable with the intensity of the characteristic radiatio
n, but the frequency of the former can be varied in a wide range. Possible
applications of the phenomenon for crystallography are discussed.