Coherent bremsstrahlung and parametric X-ray radiation from nonrelativistic electrons in a crystal

X-ray radiation generated by nonrelativistic electrons interacting with a crystal target exhibits several distinctive features in comparison to the relativistic case. The difference is related to the interference of the parametric X-ray radiation and coherent bremsstrahlung, which takes place for the nonrelativistic electrons. The characteristics of this radiation have been studied in the Bragg and Laue geometries in an electron microscope using a beam of electrons with energies in the 50 - 100 keV range. The necessary requirements on the target parameters, the measuring instrumentation, and the experimental geometry are established. Variation of the X-ray radiation frequency depending on the angle of electron beam incidence on the target in the region of nonrelativistic electron energies has been observed for the first time. The X-ray radiation frequency has been also studied as a function of the primary electron beam energy. Tunable soft X-ray radiation with quantum energy in the range below 1 keV is obtained. The radiation quantum yield per electron within a unit solid angle amounts to similar to 10(-8).