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action of relativistic electrons with a periodic medium or structure such as a single crystal. This novel radiation realization of PXR occurred in 1985 [3], and since then both theoretical and experimental studies with electrons energies E> 50 MeV have distinguished PXR as having very high spectral intensity within a narrow angular and spectral range on the order of 103 [4,7]. In addition to Si as a PXR radiating crystal, PXR emitted from othe