Laboratory Scale X-ray Fluorescence Tomography: Instrument Characterization and Application in Earth and Environmental Science

Monte Carlo Simulation Aided Quantitative Laboratory X-ray Fluorescence Analysis and Its Application in Provenancing Studies for Geo-Archeological Samples

A laboratory-based X-ray fluorescence (XRF) methodology is presented for standardless quantified analysis based on a monochromatic X-ray spectrometer coupled to Monte Carlo aided quantification. This procedure will be valuable for many scientific fields (e.g. archaeology, geology, etc.) where the unique nature of the investigated samples calls for the application of non-destructive techniques. To illustrate the value of the methodology, a case study is presented where flint artefacts from the Scheldt basin are analyzed in an attempt to provenance them. So far, little geochemical research has been done in this area. Our results contribute to the creation of a database that will help assign lithic artefacts to specific geological outcrops and will aid further research in this field.

Quantitative Reconstruction of Polychromatic X-ray Fluorescence Computed Tomography Using Transmission Tomography

Through measuring the intensity of the fluorescence X-rays emitted by the elements of interest, X-ray fluorescence computed tomography (XFCT) is capable of mapping the elemental distribution inside an object without destructively sectioning it. With the recent advances in XFCT utilizing polychromatic microfocus X-ray sources, it is expected that the popularity of such imaging modality will rise further. However, XFCT suffers from self-absorption effects, which make it challenging to reconstruct the elemental distribution inside the sample accurately. For this reason, polychromatic XFCT is mainly used to retrieve the distribution of elements with a relatively high atomic number (Z) when compared to the matrix of the sample. To enable the quantitative reconstruction of trace and low Z elements with polychromatic XFCT, a novel reconstruction method has been proposed in this manuscript. Through examining the proposed method on both simulation data and experimental data, its capacity on retrieving the density distribution of relatively low Z elements has been confirmed.

Integrated Three-Dimensional Microanalysis Combining X-Ray Microtomography and X-Ray Fluorescence Methodologies

A novel 3D elemental and morphological analysis approach is presented combining X-ray computed tomography (μCT), X-ray fluorescence (XRF) tomography, and confocal XRF analysis in a single laboratory instrument (Herakles). Each end station of Herakles (μCT, XRF-CT, and confocal XRF) represents the state-of-the-art of currently available laboratory techniques. The integration of these techniques enables linking the (quantitative) spatial distribution of chemical elements within the investigated materials to their three-dimensional (3D) internal morphology/structure down to 1-10 μm resolution level, which has not been achieved so-far using laboratory X-ray techniques. The concept of Herakles relies strongly on its high precision (around 100 nm) air-bearing motor system that connects the different end-stations, allowing combined measurements based on the above X-ray techniques while retaining the coordinate system. In-house developed control and analysis software further ensures a smooth integration of the techniques. Case studies on a Cu test pattern, a Daphnia magna model organism and a perlite biocatalyst support material demonstrate the attainable resolution, elemental sensitivity of the instrument, and the strength of combining these three complementary methodologies.

Application toward Confocal Full-Field Microscopic X-ray Absorption Near Edge Structure Spectroscopy

Using X-ray absorption near edge structure (XANES) spectroscopy, information on the local chemical structure and oxidation state of an element of interest can be acquired. Conventionally, this information can be obtained in a spatially resolved manner by scanning a sample through a focused X-ray beam. Recently, full-field methods have been developed to obtain direct 2D chemical state information by imaging a large sample area. These methods are usually in transmission mode, thus restricting the use to thin and transmitting samples. Here, a fluorescence method is displayed using an energy-dispersive pnCCD detector, the SLcam, characterized by measurement times far superior to what is generally applicable. Additionally, this method operates in confocal mode, thus providing direct 3D spatially resolved chemical state information from a selected subvolume of a sample, without the need of rotating a sample. The method is applied to two samples: a gold-supported magnesia catalyst (Au/MgO) and a natural diamond containing Fe-rich inclusions. Both samples provide XANES spectra that can be overlapped with reference XANES spectra, allowing this method to be used for fingerprinting and linear combination analysis of known XANES reference compounds.