Higher order parametric x-ray spectra in mosaic graphite and single silicon crystals

We have observed up to eight orders (n) in the spectra of parametric x-radiation, in the range 5-40 keV, produced by interaction of a 90-MeV electron beam with mosaic graphite and 90 and 35 MeV beams with single Si crystals, Measured yields and intensity ratios, I(n{ge}2)/I(n=1), in graphite are not in agreement with PXR theory for mosaic crystals. In comparison, yield and ratios of intensities in Si are close to preductions for perfect crystals. Bandwidths of spectral lines measured in both Si and graphite are in good agreement with theory and are determined by the angular field of view of the detector