Measurement and calculation of the spatial and spectral distribution of wavelength shifter radiation at BESSY

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Abstract
Calculable synchrotron radiation (SR) from BESSY dipole magnets has been used by PTB for radiometry from the visible to the soft x‐ray region with very low uncertainties for many years. The use of wavelength shifter (WLS) radiation bears the potential of extending the usable spectral range for radiometry with calculable SR to higher photon energies. Initial investigations on the feasibility of this approach have been performed: an energy dispersive high‐purity germanium detector (HPGe) was used to characterize the radiation of the new BESSY WLS with a magnetic field of B=3.2 T. The HPGe detector has previously been calibrated and so the absolute spectral photon flux could be determined. The measured spectral photon flux was then compared to calculations and good agreement was found in the order of ±5%. Although this is to our knowledge the best agreement demonstrated so far for an absolute comparison of measured WLS radiation to calculations, further improvements are needed for a future radiometric use of WLS radiation. This will be discussed.