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

Each individual particle separately using the

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each individual particle separately using the laboratory micro-XRF system or EPMA measurements. The Monte Carlo based standardless quantification method for both EPMA and micro-XRF was tested using particulate standards with known composition. Relative deviations in the range of 5–20% have been achieved by the Monte Carlo quantification scheme, depending on the analyzed element and sample type [359, 360, 367, 376]. Errors in the quantitative results are mostly due to the uncertainties in the physical constants (cross sections, fluorescence yields, transition probabilities, etc.) applied in the simulations and due to uncertainties concerning various instrumental parameters. The latter includes uncertainties in the employed excitation spectrum in case of a given polychromatic X-ray source, and often insufficient knowledge on the used detector response-function characterizing the energy dispersive detector in the experiment. Application Examples of Single Particle Analysis The applicability of the MC code for the quantitative trace-element analysis was demonstrated on low-density particles [367]. Examples for the combined application of micro-XRF and EPMA are shown for individual soil [377] and river sediment [378] particles. As the simulation code can predict reliably the measured XRF intensities (and sensitivities) for particulate standards [367], the model could be ap- plied for the quantitative analysis of unknown soil particles originating from Kosovo, based on the iterative adaptation scheme discussed above. The micro- XRF measurements were carried out at the D09B-XRF beamline of LNLS
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Methodological Developments and Applications 633 Table 7.18. Elemental composition of three soil particles calculated using the Monte Carlo quantification scheme for micro-XRF Concentration (wt%) Elements Particle 1 Particle 2 Particle 3 O a 47.2 49.2 37.6 Mg a 4.7 4.8 3.9 Al a 15.3 15.9 11.4 Si a 20.5 21.3 17.11 P 0.4 < DL < DL S 0.3 < DL < DL K 1.6 2.1 7.8 Ca 7.6 2.9 1.7 Ti 0.3 0.5 0.7 V 0.007 0.006 0.02 Cr 0.006 0.01 0.01 Mn 0.03 0.13 0.005 Fe 1.91 2.98 0.09 Co 0.007 < DL < DL Ni 0.002 0.004 < DL Cu 0.002 0.003 0.003 Zn 0.004 0.008 0.002 U 0.13 0.20 18.2 The matrix composition (O, Mg, Al, Si) was assumed as the average composition of soil obtained from electron probe microanalysis Relative standard deviations are in the range of 2–15%. a Calculated from EPMA. (Campinas, Brazil), using white beam excitation. As an example, the calcu- lated elemental compositions of three typical individual particles are shown in Table 7.18, corresponding to particles having elevated U concentrations. In these calculations, the matrix composition was estimated by EPMA, based on a Monte Carlo quantification procedure for electron interactions [359, 360]. In Fig. 7.123, the experimental and the corresponding simulated XRF spectra of a soil particle (Particle 1 in Table 7.18) measured by the LNLS micro-XRF setup is shown. The agreement between the measured and simulated spectra is satisfactory for this particle; both with respect to the fluorescence line and scatter background intensities.
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  • Spring '14
  • MichaelDudley

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