DETECTOR BASED RADIOMETRY WITH CRYORADIOM ETERS AND MONOCHROMATIZED SYNCHROTRON-RADIATION

Detector based radiometry can be extended from the uv into the vacuum uv spectral range by the use of electrically calibrated thermal detect ors at liquid helium temperatures (cryogenic radiometers) as primary d etector standards in combination with monochromatized synchrotron radi ation. Applying cryogenic radiometers with absorber discs, uncertainti es for the measurement of radiant power of less than 2 % were achieved for photon energies above 90 eV. First investigations in the spectral range below 7 eV, which employed a cryogenic radiometer with cavity a bsorber, yielded art uncertainty of 1 % for the measurement of radiant power. Thus, detector based radiometry in almost the entire spectral range below 3,5 keV can already be realized at the electron storage ri ng BESSY I with the small uncertainty of 1 % The considerably higher s pectral radiant powers of the wigglers/undulators at BESSY II will all ow for further reduction of this uncertainty.