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X-ray fluorescence using a standardless method
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Overview and calculation of X-ray K-shell transition yields for comprehensive data libraries
Publication . Martins, Luís; Amaro, Pedro; Pessanha, Sofia; Guerra, Mauro; Machado, Jorge; Carvalho, Maria Luisa; Santos, José Paulo; Indelicato, Paul; LIBPhys-UNL; DF – Departamento de Física; John Wiley & Sons, Ltd.
The simulation of atomic relaxation relies on data libraries with tabulated partial fluorescence yield values of radiative transitions, commonly derived from the Evaluated Atomic Data Library (EADL). However, recent studies support that the data library EADL could be improved by adopting Scofield's Hartree-Fock calculations instead of current Scofield's Hartree-Slater calculations. This work presents a bibliography overview of relevant atomic parameter values in order to verify the partial fluorescence yields presented in EADL. The references include libraries and articles, in which the atomic parameter values were theoretically calculated, experimentally measured, or obtained with semi-empirical and empirical fitting formulas. We present a comparison of total K-shell fluorescence yields and partial K-L2, K-L3, K-M2, K-M3 fluorescence yields that are either obtained directly from its references, or are derived from atomic parameters presented in these references. Additionally, we obtain comprehensive partial fluorescence yield values from the combination of semi-empirical and empirical fitting functions from different references. The comparisons performed in this work confirm that total K-shell, partial K-L2, and partial K-L3 fluorescence yield values, obtained from Scofield's Dirac-Slater calculations have better agreement with the most recent empirical values. Partial K-M2, and partial K-M3 fluorescence yield values obtained from Scofield's Dirac-Fock calculation have better agreement with the most recent empirical values. Therefore, further studies should be performed before changing the EADL data library.
X-ray fluorescence analysis using a standardless method
Publication . Martins, Luís de Souto; Santos, José; Carvalho, Maria Luísa
Energy Dispersive X-ray Fluorescence spectrometry (EDXRF) is a non-destructive analytical
technique that allows multi-element analysis of a large variety of materials in a
relatively fast and simple way, and is used in a broad range of areas. This technique
resorts to calibrated standard samples for each type of sample to be analysed, as well
as the knowledge of Fundamental Parameters (FP). The use of standards have several
drawbacks to consider such as the unavailability of standards for certain types of materials,
the associated monetary costs, and inaccuracy of the standard’s measurements.
On the other hand, the inaccuracy of Fundamental Parameters limits the accuracy of the
quantification. Furthermore, FP used by quantification software are included in built-in
tabulation inaccessible to the user.
EDXRF spectrometers employed in triaxial geometry allow the experimental measurement
of the Rayleigh-to-Compton scattering intensity ratio. The measurement of these
ratios of standard samples permits a method for determination of the average atomic
number Zavg of unknown samples. In this work, using the Geant4 toolkit, a code is implemented
to simulate the X-ray spectrum obtained from employing a triaxial geometry
spectrometer, aiming for both elemental quantification from the characteristic peaks and
the determination of Compton-to-Rayleigh scattering ratio. Simulation results are compared
with experimental measurements of standard reference materials, showing a good
agreement for the simulated peak intensities, as well as for the simulated scattering ratios.
Zn K-shell FP are calculated using the multiconfiguration Dirac-Fock approach, presenting
good agreement when comparing with the available values in literature. A comparison
of K-shell fluorescence yield and partial fluorescence yield values is presented, regarding
different references from which a comprehensive set of values can be used for atomic
relaxation libraries. These comparisons point that further studies should be employed
before changing Geant4 library for atomic relaxation.
Multiconfiguration Dirac–Fock calculations of Zn K-shell radiative and nonradiative transitions
Publication . Martins, Luís; Amaro, Pedro; Pessanha, Sofia; Guerra, Mauro; Machado, Jorge; Carvalho, Maria Luisa; Santos, José Paulo; LIBPhys-UNL; DF – Departamento de Física; John Wiley & Sons, Ltd.
Zinc K-shell radiative and radiationless transition rates are calculated using the multiconfiguration Dirac–Fock method. Correlation up to the 4p orbital is included in almost all transition rate calculations. Calculated radiative transition rates and transition probabilities are compared with Scofield's Dirac–Hartree–Slater and Dirac–Hartree–Fock calculations, presenting good agreement with the later. Radiative transition intensity ratios involving the strongest lines are compared with theoretical, experimental, and empirical-fit values. Most ratios are in close agreement with the empirical-fit values from NIST's Fundamental Parameters database. Calculated radiationless transition rates and ratios are compared with Chen et al.'s Dirac–Fock values and Safronova et al.'s Dirac–Fock values. The K-LL transition rates are overall lower than Chen et al.'s values, whereas the K-LX and K-XY transition rates are overall higher. Calculated K-LX/K-LL and K-XY/K-LL ratios are relatively close to the experimental values compared. Some calculated intensities relative to K-L2(1D2) are in good agreement with the experimental values, whereas others present worse agreement. The calculated fluorescence yield is higher than all theoretical, experimental, and empirical-fitted values compared, probably because the total radiationless transition rate value calculated in the present work is relatively low.
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Fundação para a Ciência e a Tecnologia
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PD/BD/105919/2014