DETERMINATION OF FLUORESCENCE YIELDS USING MONOCHROMATIZED UNDULATOR RADIATION OF HIGH SPECTRAL PURITY AND WELL-KNOWN FLUX, B. Beckhoff, G. Ulm, pp. 349-354

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. INTRODUCTION AND METHODICAL CONCEPT The more sophisticated applications of energy-dispersive X-ray fluorescence analysis (EDXRF) in the soft X-ray range, such as material and surface analysis, require improved accuracy of fundamental atomic data for standard-free quantification. With respect to the latter, improving the accuracy of both the absorption and fluorescence cross section values in the energy range below 2 keV becomes a major task. The present work focuses on the K-shell fluorescence yields of boron and carbon. Nowadays, synchrotron radiation is used to investigate fundamental atomic processes. Synchrotron radiation of high spectral purity is an efficient tool to determine not only fundamental atomic data with a high accuracy, but also the efficiency and response function of X-ray detectors. Well-characterized radiation sources and detection systems are crucial for the measurement of fluorescence cross sections. The plane grating monochromator beamline [l] for undulator radiation in the PTB radiometry laboratory at BESSY II provides monochromatic radiation of high spectral purity. By accurately measuring the radiant power of monochromatized radiation with an electrical substitution radiometer and controlling the stored electron heam current, photodiodes and energy-dispersive detectors [2] can be calibrated. Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol.44 348 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol.44 349