DETERMINATION OF FLUORESCENCE YIELDS USING MONOCHROMATIZED UNDULATOR RADIATION OF HIGH SPECTRAL PURITY AND WELL-KNOWN FLUX

Along with the increasing importance of material and surface analysis by means of X-ray fluorescence analysis (XRF) in the soft X-ray range, the need for standard-free quantitication modes has grown. Here, improving the knowledge of accurate values of the fluorescence yields for photon energies below 2 keV becomes a major task. For this purpose, an irradiation chamber was built by the Physikalisch-Technische Bundesanstalt (PTB), Germany’s national metrology institute. This UHV chamber allows an accurate positioning of up to 6 specimens with respect to a set of high purity Al diaphragms defining exactly the excitation beam size and the solid angles of radiation detection. The scattered and fluorescence radiation was registered by a calibrated semiconductor detector. The monitoring of the monochromatized excitation radiation by means of calibrated photodiodes was ensured. For the specimen excitation, the plane grating monochromator beamline of the PTB for undulator radiation at the electron storage ring BESSY II, involving a high spectral purity, was used. In the present investigation, the fluorescence yields associated with the K-edge of boron and of carbon were determined for different mass depositions of the respective elements. The results of the initial experiments, including the achieved accuracy, are given.