CRYSTAL SPECTROSCOPY OF X-RAY SYNCHROTRON SOURCE BRIGHTNESS

Photon intensities in a monochromatic beam obtained by a horizontal Bragg reflection of synchrotron radiation by a monochromator crystal are compared for the three perfect crystals: silicon and germanium in symmetric (111) reflection and Diamond (C*) in asymmetric (111) transmission geometry. Consistent results are obtained within relative bandwidths spanning a factor of 50 from Si (333) to Ge (111) and within a wavelength range form 0.4 angstrom to 1.6 angstrom. Results using a mosaic Be crystal within the same wavelength range depend in this work on a model of the mosaicity of the Be crystal. However, if the reflectivity of the Be crystal is determined experimentally for a few selected wavelengths, it is not necesseary to invoke a mosaic model and a Be crystal may serve the purpose of characterizing the synchrotron beam as well as a perfect crystal. Thin diamond and beryllium crystals in transmission are particularly convenient for spectroscopy of very powerful beams from third generation synchrotron sources, because these low-Z elements absorb only a tiny fraction of the beam power.