Observation of parametric X-ray radiation in an anomalous diffraction region

• Parametric X-ray radiation below the low energy threshold for diffraction of free X-rays.
• Experimental separation of the contributions from different radiation mechanisms.
• PXR from relativistic electrons in mosaic crystals and textured polycrystlas.

A new possibility to expand the energy region of diffraction processes based on the interaction of relativistic charged particles with crystalline structures is presented. Diffracted photons related to parametric X-ray radiation produced by relativistic electrons are detected below the low energy threshold for the X-ray diffraction mechanism in crystalline structures for the first time. The measurements were performed during the interaction of 7 MeV electrons with a textured polycrystalline tungsten foil and a highly oriented pyrolytic graphite crystal. The experiment results are in good agreement with a developed model based on the PXR kinematical theory. The developed experimental approach can be applied to separate the contributions of real and virtual photons to the total diffracted radiation generated during the interaction of relativistic charged particles with crystalline targets.