When virtual photons produced by charged particles passes crystal and are diffracted by crystal lattice in the mode of Bragg or Laue geometry
they can form a kind of X-ray radiation named parametric X-ray radia-tion(PXR)
PXR has a serious of characters: linearly polarized
quasi monochromatic
smoothly tunable
narrow width of energy
high efficiency of photo/electron conversion.Electrons in MeV and GeV energies can be used to produce PXR.There are also some aspects of potential application about PXR.