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

Chemical compositions reference values intensities

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Chemical compositions (reference values), intensities, and mass attenuation coefficients C(Chem) Concentration determined Standard ppm ppm LINREG COMPT JEC SY-2 8.6 6.5 6.9 8.4 SO-3 W 5.5 4.0 3.7 5.3 73326 12.7 11.3 10.3 13.1 73325 97 104.6 132.7 100.1 73324 7.6 5.3 4.8 5.0 73321 5.5 4.8 3.6 5.1 73319 14.2 13.8 11.6 14.0 TR-006 431.0 444.9 435.8 433.7 TR-013 889.0 882.4 886.0 887.5 RMS (ppm) 6.2 12.6 1.8 Values of the concentrations found using simple linear regression (LINREG), Compton correction (COMPT) and jump edge correction (JEC). The analysis of cobalt in the samples concerned is hampered by the fact that the Fe K-absorption edge is located between the wavelength of the Compton scattered tube line and the Co K α . This is the reason why the Comp- ton correction does not work. It actually makes the results worse: the RMS increases from 6.2 ppm (no correction) to 12.6 ppm. This is not surprising because the Compton correction would account for a change in absorption, based on the assumption that there are no significant absorption edges be- tween the wavelength of the Compton scattered intensity ( λ s ) and the analyte wavelength ( λ i ). In the case at hand, however, the presence of a large amount of iron is responsible for a large absorption jump between λ s and λ i . By using both, the Compton scattered intensity and the jump edge correction based on the Fe K β intensity, the RMS is reduced to 1.8 ppm.
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5 Quantitative Analysis 369 This method for jump edge correction requires, however, additional mea- surements and the calculation of mass attenuation coefficients for reference samples. Also, even with jump edge correction, the method still does not correct for enhancement. 5.5 Thin and Layered Samples P.N. Brouwer XRF is an attractive technique for the analysis of thin and layered samples, because both the composition and thickness of layers can be determined in a fast and nondestructive way. The application area is growing; examples are optical coatings, protective coatings, magnetic recording materials, optical recording materials, superconductive films, as well as wafers for IC technology. The photon rates originating from thin and layered specimens depend on the composition of each of the layers as well as on the thickness of the layers. It is therefore possible to determine simultaneously the composition as well as the thickness(es). Just as in the case of bulk samples, quantification can be accomplished using calibration standards with composition close to that of the sample. Since the layer thicknesses are additional unknown quantities, additional analytical lines may be required to analyze a sample. Producing accurate thin film or layered standards is very difficult, thus more than in the case of bulk samples, FP-based analysis is demanded for thin and layered sam- ples, where reference samples are only required to determine the spectrometer sensitivity for an analytical X-ray line. The reference sample can be any type of sample of known composition: bulk, thin film, or layered. Using reference samples close to the sample composition in some cases eliminates systematic errors, which can improve the accuracy.
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