A compact tunable X-ray source based on parametric X-ray generation by moderate energy linacs

Parametric X-radiation can be described as the diffraction of virtual photons associated with the electric field of a relativistic charged particle passing through a crystal. In analogy with Bragg reflection of X-rays, these diffracted photons appear as real photons, with an energy which satisfies Bragg´s law for the reflecting crystal planes. We describe the results of experiments performed on the Naval Postgraduate School linac which were designed to explore the basic properties of PXR in order to assess its potential application as a compact tunable X-ray source. Experiments using a mosaic graphite radiator show that this radiator produced multiple order, narrow bandwidth reflections from 5-45 keV. The measured production efficiency is found to exceed that predicted for spectral orders n>1. We demonstrated the tunability of PXR by rotating the crystal in order to change the Bragg angle relative to the incident 90 MeV electron beam