[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

Commercial scanning facilities generally work in air

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silicon drift detectors enables continuous measurements at reasonable costs. Commercial scanning facilities generally work in air. Some benchtop systems can switch to vacuum conditions in order to lower the detection limits and to enable the analysis of light elements such as Na, Mg, Al. Zhdanov [446] provides details on manufacturers of micro-XRF systems in the internet. Sample Preparation Techniques In general, all types of samples are suitable for qualitative analyses, but to obtain semiquantitative or quantitative information, samples have to fulfill certain conditions. A relatively smooth polished surface is required. However, grain, pore and crystal size distribution, water and organic content, crystal orientations in the sample are properties that strongly influence the signal and may hinder the access of quantitative information [399].
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Methodological Developments and Applications 649 Fig. 7.127. Geoscanner equipped with columns Instrumentation and Methods The applications shown later have been performed on two individual in- struments, both designed by COX Analytical Systems AB, Sweden. The Itrax geoscanner (XRGS), a special design by the Bundesanstalt f¨ur Geowis- senschaften und Rohstoffe (BGR), Germany (Figs. 7.127 and 7.128), operates with flat beam optics suitable for 1D profiles, while the standard ITRAX X-ray microscope using a 100- µ m monocapillary is applicable for point mea- surements, 1D profiles, and 2D scans. Both systems are based on a Rich. Seifert & Co. ISO-DEBEYEFLEX 3003 HV-generator and the standard oper- ation voltage for the data acquisition is 45 kV at 30 mA with long fine-focused Philips XRD Mo tube type PW 2275/20 (3 kW, 60 kV). Within the XRGS the beam is focused by a glass slit capillary at 50 µ m height and 2000 µ m length. The detector is placed at an angle of 45 to the sample surface. It is an energy-dispersive, Peltier-cooled R ¨ ONTEC
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650 D. Rammlmair et al. line camera for x-ray absorption Sample Dispersive solid state x-ray detector Software eveluation Characteristic lines X-ray spectrum Analyser amplifier X-ray source X-ray optics Fig. 7.128. Schematic view of the EDXRF geoscanner (courtesy of COX Analytical Systems AB, Sweden) drift-chamber detector, with an energy resolution of 149 eV provided by a vacuum nozzle. The XRGS is further equipped with a rotating stage for six samples. The samples are scanned vertically by a line camera to find the area of interest, and after rotation to the measurement position, the sample is fo- cused and scanned by moving the X-ray tube and detector unit. Step sizes range from 50 to 200 µ m and time of exposure from 1 to 30 s according to the individual requirements. A number of elements can be chosen to be displayed on the monitor show- ing the variation of elements during the XRF scan. For each step the complete energy-dispersive spectrum is stored in 1024 channels for later evaluation.
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  • Spring '14
  • MichaelDudley

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