High-accuracy detector calibration at the PTB four-crystal monochromator beamline

A four-crystal monochromator beamline has been installed by the Physikalisch-Technische Bundesanstalt at a bending magnet of the electron storage ring BESSY II. The monochromatic radiation with very high spectral purity and high spectral resolution in the photon energy range from 1.75 to 10 keV is used to calibrate detectors by comparison to a cryogenic electrical substitution radiometer as primary detector standard with relative uncertainties well below 1%. This is one order of magnitude better than all calibrations of non-energy-dispersive detectors in this spectral range previously performed. The beamline is also used for the characterization of optical components.