We describe our recent experimental study of the production of x rays by an electron beam interacting with a crystal lattice, i.e., parametric x-ray (PX) generation. In this radiation process, the virtual photon field associated with a relativistic electron traveling in a crystal is diffracted by the crystal lattice in the same way that real x rays are diffracted by crystals. The radiation produced satisfies the Bragg conditions associated with the diffraction of the virtual photons which are nearly parallel to the velocity of the electrons. This phenomenon is associated with a more general class of radiation production mechanisms which include transition radiation (TR), diffraction radiation (DR), and Smith-Purcell radiation. In each case, radiation is produced when the particle's fields are altered by interacting with a material whose dielectric constant varies along or near the particle's trajectory. The usual acceleration mechanism for the production of radiation is not involved in these phenomena. In the case of a crystal, the periodic electric susceptibility interacting with the particle's field produces parametric x rays. We will also present a theoretical overview of this phenomenon which can be used to generate monochromatic, linearly polarized, directional x rays. Accelerators with energies ranging from a few MeV to hundreds of MeV may be used as drivers for novel parametric x-ray generators for various applications requiring the unique properties of these sources.
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