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

M in both directions the diameter of the beam is 10

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m in both directions, the diameter of the beam is 10 µ m. The spatial resolu- tion, however, is lower than step sizes due to the thickness of the sample and the alignment of sample to detector in 45 geometry. For each element, the relative K α line intensities are shown; maximum and minimum values refer to black and white pixels, respectively. Manganese, Fe, Zn, As, Br, Rb, and Cs display a rather uniform distribution throughout the inclusion. Antimony and Sn display clusters that may be related to a black daughter crystal within the inclusion. ( b ) Photomicrograph of the inclusion. ( c ) Projection of the inclusion onto a plane parallel to the detector surface primary beam as well as the fluorescence radiation is absorbed in the sample and air surrounding the inclusion. This absorption is energy- and consequently element-specific (Fig. 7.140). Therefore, for inclusion analysis, the thickness and composition of the top layer has to be exactly known for accurate depth correction and quantification. A second peculiarity of inclusion analyses is that internal standardization is generally not applicable as there is no pos- sibility to determine the concentration of one element within the inclusion, which is at the same time sensitive for SRXRF by an alternate method. One exception is Cl in high-salinity flat-lying inclusions, which may be quanti- fied by cryometric measurements of inclusions. However, Vanko et al. [522] demonstrated that an error in the thickness estimation of only 1 µ m of the overlaying matrix yields an error of several tens of percentages for elements with Z < 20. This means that results from an internal calibration to Cl, which has a Z of 17, are highly dependent on precise thickness estimation. In cases where internal calibration is impossible, the spectra may be calibrated exter- nally by the use of thin-film NIST reference materials [522, 523] or synthetic fluid inclusions [513]. Quantitative results may also be obtained in a stan- dardless mode [524] by comparison of peak areas of measured spectra and full XRF spectra simulated using a Monte Carlo code [525–528] that is applicable
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678 D. Rammlmair et al. absorption 0 0 5 10 15 20 25 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 energy (keV) Cl 10 20 30 40 50 Fe As Rb Mo Ag 5 Fig. 7.140. Energy-dependent X-ray absorption in quartz of different thicknesses. The numbers on the lines refer to thicknesses in micrometer. The position of some interesting K α lines is marked to a multilayer geometry. The achieved accuracy for this approach tested on synthetic fluid inclusions was better than approaches determining absolute concentrations by using a calibration on reference materials 17% error for concentrated inclusions and 30% close to the lower limit of detection [524]. Single inclusion analyses are extremely powerful in ore deposit studies and allow the tracing of enrichment processes. One recent example is the study of the chemical evolution of an ore-forming pegmatite-hydrothermal system at the Ehrenfriedersdorf Complex, Germany, which is genetically related to important tin–tungsten deposits [524]. Arsenic and Cu were found to prefer-
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