Vutchkov, Mitko K.; Preston, John; Lalor, Gerald C.
International Centre for Environment and Nuclear Sciences
Total Reflection X-Ray Fluorescence - Principle and applications [Abstract]
Proceedings of the First Conference of the Faculty of Natural Sciences University of the West Indies, Mona
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University of the West Indies, Mona, Kingston, Jamaica
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Faculty of Natural Sciences, University of the West Indies, Mona.
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The Total Reflection X-ray Fluorescence (TR-XRF) is the next generation in XRF technology, which was commercially introduced around 1950 as Wavelength-Disperse (WD-) and in 1980 as TR- version of the XRF technique. The TR-XRF has a distinctly improved power of detection, comparable with WD-XRF and ED-XRF. The method was suggested by Yoneda and Hotiuchi as early as 1971 and the physical principle were clarified by Wobrauschek and Aiginger. In 1980 the first commercial instrument was put on the market. The principle of the method is based on total reflection of the X-Ray tube's primary beam, which grazes the polished and optically flat surface of the same holder. As a result, the background due to the Rayleigh and Compton scattering from the sample support is suppressed and the detection power is enhanced. The sample itself is placed on the holder in the form of a thin film, obtained by pipetting and drying (water samples), freeze-drying, or ashing (biomaterials) onto a quartz carrier. Finely powdered materials (NBS coal fly ash i.e.), can be prepare as suspensions, and an aliquot can be pipetted onto the holder. The use of thin film samples makes the TR-XRF especially suitable for analysis of aqueous solutions, which was the first reported application of TR-XRF. Many liquids, particularly waters - drinking, rain, river, sea and waste, can be analyzed directly in the low ppm - ppb ranges. The TR-XRF is suitable not only for thin-film-type specimens, but the method can be used to analyze extremely thin films of or layers and the surfaces of solids, provided that they are optically flat (wafers in semiconductor technology). TR-XRF can compete by detection limits with atomic absorption neutron activation analysis, or inductively coupled plasma-optical emission spectroscopy. In addition the analytical capability of TR-XRF cover 90% of the Periodic Elements chart (Z >11), depending on the X-ray tube and the Si(Li) detector in use. The ultramicroanalysis features of TR- XRF however, impose that sample preparation procedures be done under clean laboratory requirements. The TR-XRF system, is currently being setup at the Centre for Nuclear Sciences. When completed it will be applied for sub trace analysis of water, oils, biomaterials, air particulate and other materials.....