Parametric X-Radiation (PXR)
PXR is generated in crystals due to the polarization of the lattice atoms by the traversing relativistic electrons. Since PXR can be considered as a diffraction of virtual photons, it is emitted in accordance with the Bragg rule. The pattern consists of two peaks of, in general, different intensity also valid f Compared to CR, the absolute intensity of PXR is about three orders ofmagnitude smaller. Since this is or the natural line width
the spectral densities remain quite comparable. PXR energies in the interval of (2 - 40) keV should be reached at ELBE, where Gis of the order of 1 eV. At typical emission angles ( q > 1/γ) the background due to bremsstrahlung is strongly reduced. PXR might be a promissing X-ray source in future. Possible applications are, e.g., the measurement of crystal properties like the dielectric susceptibility or the investigation of the mechanism of radiation damage of cell tissue in biophysics.