Confocal microscopic X-ray fluorescence at the HASYLAB microfocus beamline: characteristics and possibilities

Determination of mercury in polluted soils surrounding a chlor-alkali plant: Direct speciation by X-ray absorption spectroscopy techniques and preliminary geochemical characterisation of the area

In order to reduce dead time in the detector system, an organic glass is used as a scatterer. By using the backscattered spectra from the organic glass, the energy dependence of the focal spot size, transmission efficiency, divergence, and output focal distance (OFD) of the polycapillary x-ray lens (PCXRL) is measured efficiently over a broad energy range. The axial scanning method is devised to measure the energy dependence of the OFD. The halo effect is studied by measuring the spatial distribution of x rays with various energies in the beam focused by the PCXRL.

Measurements of energy dependence of properties of polycapillary x-ray lens by using organic glass as a scatterer

Polycapillary lenses permit X-rays to be focused down to relatively small (<50 μm) beam diameters. A polycapillary device, suitable for focusing of synchrotron radiation, was characterized at beam line L of HASYLAB (Hamburg, Germany). Beam parameters such as beam size, transmission efficiency and gain in flux density were determined as a function of the energy of the primary monochromatic beam entering the polycapillary. At a distance of 4 mm between the lens tip and the sample, the smallest beam diameters were recorded: 30 μm at 7 keV, decreasing to 8 μm at 21 keV. In the energy range from 7 to 15 keV, the transmission efficiency varied between 30 and 45%, while the maximum gain in flux density was calculated to be around 3500. When the energy was changed from 7 to 30 keV, a vertical translation of only 7-8 μm was observed, indicating that this optic is highly suitable for use in μ-XANES investigations. To illustrate this point, the investigation of paper corrosion due to iron gall inks and the speciation of Ni in environmental particles is described.

/pdf/characterization-of-a-polycapillary-lens-for-use-in-micro-550v19vbal.pdf

Characterization of a polycapillary lens for use in micro‐XANES experiments

X-rays were discovered by Röntgen in 1878 and were first considered to be a mysterious type of radiation with properties very different from electromagnetic radiation in the ultraviolet, visual and infrared range of the spectrum: Röntgen’s first experiments suggested that X-rays could not be reflected, refracted or polarized but instead penetrated fairly deeply into materials, apparently without causing harm or other (permanent) changes. Although it is now well documented that X-rays exhibit analogous characteristics to the radiation of longer wavelengths and that high doses of this type of radiation on (biological) tissues can effectively induce discolourations and other damages, irradiation of inorganic materials with X-rays is generally considered not to cause them any harm. Thus, next to being used for radiographic purposes (see Chapter 2), X-rays are also frequently employed for compositional and structural analysis of cultural heritage (and many other) materials. A well-established method of quantitative element analysis is X-ray fluorescence (XRF) analysis, which is based on the ionization of the atoms of the material being investigated by an energetic beam of primary X-rays. The characteristic radiation that is emitted by the ionized atoms upon relaxation contains information on the nature and the abundance of the elemental constituents present. Since XRF meets a number of the requirements of the “ideal method” for non-destructive analysis of cultural heritage materials (see Chapter 1) [1], analysis of objects of artistic and/or archaeological value with conventional XRF is fairly common; it is in fact one of the most often applied methods for obtaining qualitative and semi-quantitative information on the materials these objects are made of [2]. Several textbooks cover the fundamental and methodological aspects of the method and its many variants [3]. In the

X-ray based methods of analysis

In this study a monolithic polycapillary half-lens was evaluated as a micro-focusing device for monochromatic synchrotron radiation. The tested optic produced an X-ray micro-beam of 37–53 microns in the energy range of 6–19 keV with a maximum intensity gain of about 600 with respect to the primary beam. When applied to X-ray fluorescence (XRF) analysis, absolute detection limits in the range of 0.06–1 pg were measured, coupled with relative detection limits of 0.3–200 ppm for the atomic number range of 20–40. The use of the polycapillary lens was demonstrated by performing microscopic X-ray absorption near edge structure (XANES) measurements in fluorescence mode on transition metals (concentration range 40–100 ppm) in fly ash particles.

Suitability of polycapillary optics for focusing of monochromatic synchrotron radiation as used in trace level micro-XANES measurements

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Suitability of polycapillary optics for focusing of monochromatic synchrotron radiation as used in trace level micro-XANES measurements