  Spectra of parametric X-ray radiation (PXR) are considered in the range of
anomalous dispersion for one of the atoms in a crystal elementary cell. The PXR
spectra are calculated both for the ultra-relativistic and non-relativistic
electrons for the specific conditions corresponding to the organic compounds .
It is shown that analysis of the RXR angular distribution permits one to
realize the method of anomalous scattering for direct measurement of the phases
of structure amplitudes without additional isomorphic intrusion of a heavy
atom.
