Marcelo Rubio

Synchrotron radiation X-Ray fluorescence at the LNLS: beamline instrumentation and experiments

The x-ray fluorescence heamline of the Laboratorio Nacional de Luz Sincrotron (LNLS) is described. The main optical component of the beamline is a silicon (111) channel-cut monochromator, which can tune energies between 3 and 14 keV. A general description of two experimental stations is given. Beam characterization was done by measuring experimental parameters such as vertical profile and monochromatic flux. These results show that the photon flux at 8 keV in an area of 20 mm 2 is 4.2 × 10 9 photons s -1 . The possibility of achieving fine tuning of energies (high resolution) was confirmed. This paper presents some original results derived from the commissioning of the beamline, such as a comparison of detection limits in different experimental conditions, and a novel mechanical system to align capillaries together with a semi-automatic adjustment procedure. So far, there have been several proposals to perform a variety of experiments at this beamline, covering different fields, such as physics, chemistry, geology and biology.

Association between As and Cu renal cortex accumulation and physiological and histological alterations after chronic arsenic intake.

Arsenic (As) is one of the most abundant hazards in the environment and it is a human carcinogen. Related to excretory functions, the kidneys in humans, animal models or naturally exposed fauna, are target organs for As accumulation and deleterious effects. Previous studies carried out using X-ray fluorescence spectrometry by synchrotron radiation (SR-microXRF) showed a high concentration of As in the renal cortex of chronically exposed rats, suggesting that this is a suitable model for studies on renal As accumulation. This accumulation was accompanied by a significant increase in copper (Cu) concentration. The present study focused on the localization of these elements in the renal cortex and their correlation with physiological and histological As-related renal effects. Experiments were performed on nine male Wistar rats, divided into three experimental groups. Two groups received 100 microg/ml sodium arsenite in drinking water for 60 and 120 consecutive days, respectively. The control group received water without sodium arsenite (< 50 ppb As). For histological analysis, 5-mum-thick sections of kidneys were stained with hematoxylin and eosin. Biochemical analyses were used to determine concentrations of plasma urea and creatinine. The As and Cu mapping were carried out by SR-microXRF using a collimated white synchrotron spectrum (300 microm x 300 microm) on kidney slices (2 mm thick) showing As and Cu co-distribution in the renal cortex. Then, renal cortical slices (100 microm thick) were scanned with a focused white synchrotron spectrum (30 microm x 30 microm). Peri-glomerular accumulation of As and Cu at 60 and 120 days was found. The effects of 60 days of arsenic consumption were seen in a decreased Bowmans space as well as a decreased plasma blood urea nitrogen (BUN)/creatinine ratio. Major deleterious effects; however, were seen on tubules at 120 days of exposition. This study supports the hypothesis that tubular accumulation of As-Cu may have some bearing on the arsenic-associated nephrotoxicological process.

Mathematical model for evaluation of surface analysis data by total reflection XRF

The general problem of an electromagnetic wave moving through a stratified medium appears naturally in all the techniques associated with surface analysis by total reflection. It is a consequence of the theoretical models that describe that describe the physical processes involved in these techniques. This problem has been extensively studied owing to its importance in optics. The mentioned techniques are known as grazing incidence x-ray fluorescence (GIXRF) and grazing exit x-ray fluorescence (GEXRF). In this work, the electric field in a stratified medium was calculated using basic mathematical tools. The model uses a matrix approach to take advantage of well-known mathematical results (such as Hessenbergs matrix properties). In this way, the model optimizes and facilitates the data analysis in GIXRF measurements and GEXRF experiments. The simplicity of the formalism admits approximations of the electric field, which allow a better understanding of the experimental data in both techniques. The model was used to analyze experimental data on silicon wafers with surface layers of different elements, showing excellent results.

Surface analysis by total-reflection X-ray fluorescence

Abstract This work shows the feasibility of surface analysis though the detection of characteristic fluorescent radiation in the total-reflection regime. A theoretical formalism to correlate surface parameters with X-ray fluorescence intensities from multiple-layer samples was developed. Experimental measurements were performed in the Microanalysis Station of the Frascati National Laboratory, Italy. The samples were Si wafers with surface layers of different thicknesses of Cr. The angular dependence of the Kα fluorescent intensity emitted by Cr was recorded with a Si(Li) detector, and the obtained data were fitted to the correspondent theoretical expression. Our results agreed very well with the values measured during sample fabrication. Diffusion processes of the surface layer into the substrates were also considered. They were analysed assuming a middle layer between the surface layer and the substrate.

L-subshell Coster-Kronig yields measured with synchrotron radiation

Abstract The synchrotron photoionization method was applied to measure L -subshell Coster-Kronig yields. This method is based on the capability of tuning the energy of the synchrotron photons producing a selective subshell ionization. Two foil samples of Yb and Ta were irradiated and their characteristic spectra were recorded. Data were analyzed using a new formalism (based on a matrix representation) for expressing X-ray fluorescence intensities involving Coster-Kronig transitions. The results obtained in this work are f 12 = 0.249 ± 0.021, f 13 = 0.408 ± 0.055 and f 23 = 0.186 ± 0.040 for Yb, and f 12 = 0.168 ± 0.039, f 13 = 0.322 ± 0.072 and f 23 = 0161 ± 0.053 for Ta. These data are very reliable and represent a valuable information for spectroscopists, considering the lack of data for L -shell parameters.

A method of XRF spectrochemical analysis based on some geometrical properties of the X-ray fluorescent intensity

Abstract In previous works [J.E. Fernandez and M. Rubio, subm. to X-Ray Spectrom. (1989); J.E. Fernandez, subm. to Comput. Phys. Commun. (1989)] it was found out that the primary-XRF (X-ray fluorescence) intensity remains invariant under variation of the tilt angle α of the propagation plane whilst the secondary one vanishes at the limit |αz.sfnc; → π 2 . As a consequence the detected fluorescence is only composed of primary photons, simplifying the increasing complexity, for multicomponent samples, of the mathematical dependence of the XRF intensity on their composition. This feature is exploited to elaborate analytical methods based on the resulting simplified XRF-intensity expression. The sample composition is calculated as solution of a linear set of equations when the excitation spectrum is monochromatic, and as iterative solution of a nonlinear set of equations for the more realistic polychromatic excitation spectrum. For polychromatic excitation an additional method is devised, which uses some nonlinear least-squares coefficients and tabulated data to build the coefficients matrix of a linear system of equations whose solution is the required concentration. Measured intensities under this scheme were used to determine the major-elements composition of some NBS standard steels. Comparison with NBS reported values evidences that this method is reliable and precise.

Corrections to the X-ray fluorescence equations considering double K-photoionization

Some of the most common multi-electron transition processes are described and the effects of a double K-photoionization are analysed. Some previous experimental results are summarized, and the fact that fundamental parameters (such as absorption edge jump ratios) are changed through double ionization is shown. Finally, a correction to the equations for X-ray fluorescence intensity due to the effects of the double K-ionization is proposed by the inclusion of a step-function in the emission factor used in fundamental parameters calculation.

Evidence of double K-photoionization in P, Cl, and K

Abstract Measurements of the Kα-line from pure samples of phosphorus (Z=15), chlorine (Z=17), and potassium (Z=19) were carried out. The samples were excitated using monochromatized synchrotron radiation of different energies. Experimental evidence of the presence of double K-holes and their effects on X-ray-fluorescent spectra is reported.

Quantification of Multilayer Samples by Confocal μXRF

The confocal setup consists of x‐ray lenses in the excitation as well as in the detection channel. In this configuration, a micro volume defined by the overlap of the foci of both x‐ray lenses is analyzed. Scanning this micro volume through the sample, 1–3 dimensional studies can be performed. For intermediate thin homogeneous layers a scanning in the normal direction to the surface sample provides information of its thickness and elemental composition. For multilayer samples it also provides the order of each layer in the stratified structure. For the confocal setup, we used a glass monocapillary in the excitation channel and a monolithic half polycapillary in the detection channel. The experiment was carried out at the D09B beamline of the LNLS using white beam. In the present work, a new algorithm was applied to analyze in detail by confocal μXRF a sample of three paint layers on a glass substrate. Using the proposed algorithm, information about thickness and elemental densities was obtained for each l...

Influence of the propagation-plane inclination angle on the fluorescent intensity: Study of the emission of small-thickness samples and determination of the maximum emission angle

Abstract A theoretical study of the fluorescent intensity emitted by a small-thickness multicomponent specimen is carried out and a strong dependence on the inclination angle α of the propagation plane is found. The existence of one angular value αM at which the total fluorescent emission achieves a maximum is demonstrated, and it is found that such an angle depends essentially on the sample thickness and composition. Calculating αM by means of the theoretical model, it is possible to select the optimal excitation detection configuration to reach the maximum fluorescent intensity compatible with the characteristics of thickness and composition of the observed sample. Inversely, the thickness of a sample of known composition can be estimated by means of the experimental determination of the angle αM. However, it was found that this thickness measuring method has a very poor sensitivity. The theoretical results have been confirmed by Monte Carlo simulation.