Karen Rickers

Visualization of a Lost Painting by Vincent van Gogh Using Synchrotron Radiation Based X-ray Fluorescence Elemental Mapping

Vincent van Gogh (1853-1890), one of the founding fathers of modern painting, is best known for his vivid colors, his vibrant painting style, and his short but highly productive career. His productivity is even higher than generally realized, as many of his known paintings cover a previous composition. This is thought to be the case in one-third of his early period paintings. Van Gogh would often reuse the canvas of an abandoned painting and paint a new or modified composition on top. These hidden paintings offer a unique and intimate insight into the genesis of his works. Yet, current museum-based imaging tools are unable to properly visualize many of these hidden images. We present the first-time use of synchrotron radiation based X-ray fluorescence mapping, applied to visualize a womans head hidden under the work Patch of Grass by Van Gogh. We recorded decimeter-scale, X-ray fluorescence intensity maps, reflecting the distribution of specific elements in the paint layers. In doing so we succeeded in visualizing the hidden face with unprecedented detail. In particular, the distribution of Hg and Sb in the red and light tones, respectively, enabled an approximate color reconstruction of the flesh tones. This reconstruction proved to be the missing link for the comparison of the hidden face with Van Goghs known paintings. Our approach literally opens up new vistas in the nondestructive study of hidden paint layers, which applies to the oeuvre of Van Gogh in particular and to old master paintings in general.

Real-World Emission Factors for Antimony and Other Brake Wear Related Trace Elements: Size-Segregated Values for Light and Heavy Duty Vehicles

Hourly trace element measurements were performed in an urban street canyon and next to an interurban freeway in Switzerland during more than one month each, deploying a rotating drum impactor (RDI) and subsequent sample analysis by synchrotron radiation X-ray fluorescence spectrometry (SR-XRF). Antimony and other brake wear associated elements were detected in three particle size ranges (2.5-10, 1-2.5, and 0.1-1 microm). The hourly measurements revealed that the effect of resuspended road dust has to be taken into account for the calculation of vehicle emission factors. Individual values for light and heavy duty vehicles were obtained for stop-and-go traffic in the urban street canyon. Mass based brake wear emissions were predominantly found in the coarse particle fraction. For antimony, determined emission factors were 11 +/- 7 and 86 +/- 42 microg km(-1) vehicle(-1) for light and heavy duty vehicles, respectively. Antimony emissions along the interurban freeway with free-flowing traffic were significantly lower. Relative patterns for brake wear related elements were very similar for both considered locations. Beside vehicle type specific brake wear emissions, road dust resuspension was found to be a dominant contributor of antimony in the street canyon.

In-situ determination of mineral solubilities in fluids using a hydrothermal diamond-anvil cell and SR-XRF: Solubility of AgCl in water

Abstract A hydrothermal diamond-anvil cell has been designed for the in situ analysis of the concentration of elements in fluids and melts using synchrotron radiation X-ray fluorescence. This technique permits determination of the solubility of minerals in fluids at high pressures and temperatures (tested to 1.1 GPa and 800 ℃). Further advantages include multi-element analytical capability and applicability for sparingly soluble compounds, for congruent or incongruent dissolution, and for studies of dissolution kinetics. The solubility of AgCl(s) in water was determined at 300 to 450 ℃ and pressures to 760 MPa. The molality of silver in the fluid was obtained from density corrected Kα peak areas by calibration to the known solubility at 300 ℃ and vapor pressure and, standardless, by comparison with Monte- Carlo simulated spectra. The results from both methods were internally consistent and in good agreement with literature data for comparable P-T conditions.

Low-temperature Zr mobility: An in situ synchrotron-radiation XRF study of the effect of radiation damage in zircon on the element release in H2O + HCl ± SiO2 fluids

Abstract The release of Zr, U, and Pb from nearly metamict zircon and its recrystallized analog and of Zr from fully crystalline and slightly radiation-damaged zircon in H2O + HCl ± SiO2 fluids was investigated in situ at temperatures between 200 and 500 °C using a hydrothermal diamond-anvil cell and time-resolved synchrotron-radiation XRF analyses. Dissolution of nearly metamict zircon proceeded much faster than that of zircon with little or no radiation damage and resulted in a 1.5 to 2 log units higher Zr molality in 6 to 7 m HCl fluids. Extensive recrystallization of the almost fully amorphous material started at 260 to 300 °C in H2O + HCl, and at about 360 °C if quartz was added, and was coupled with a decrease of the Zr concentration in the fluid by more than an order of magnitude. Recrystallization in 7 m HCl had little effect on the aqueous U and Pb concentrations, whereas addition of quartz caused a more sluggish decrease of the Zr concentration in the fluid upon recrystallization and lowered the release of U. The data presented here support the interpretation that enhanced Zr mobility in low-grade metamorphic rocks may be related to dissolution of metamict zircon by aqueous fluids and illustrate the significance of the silica activity on the kinetics of dissolution and recrystallization during zircon-fluid interaction.

The oxidation state of iron determined by Fe K-edge XANES—application to iron gall ink in historical manuscripts

Fe K-edge XANES measurements were performed to determine the oxidation state of iron in iron gall inks. These data are used to investigate the relationship between the Fe oxidation state and ink corrosion in historical manuscripts. The oxidation state is determined using the pre-edge based on a general variation trend that was derived from model compounds and validated here independently on a suite of samples with known oxidation state and Fe in octahedral coordination (i.e. similar to Fe in gall ink). As long as suitable references for the pure ferric and ferrous state of iron gall inks cannot be pointed out, the analysis of the pre-edge of the Fe K-edge represents the only way to acquire absolute values for the Fe oxidation state (Fe3+/Fetot) with spatial resolution for this usually non-crystalline compound. Fe3+/Fetot values for the ink samples vary between ca. 0.7 and 1.0. Spatially resolved analyses performed across ink strokes of various historical manuscripts as well as newly made samples did not reveal any systematic spatial dependence. On average, historical samples that were exposed to conservation treatments show a more oxidized state. However, the measurements demonstrate explicitly that the exposure to X-rays during the XANES acquisition affects the oxidation state of Fe in most iron gall inks.

Waterborne versus dietary zinc accumulation and toxicity in Daphnia magna: A synchrotron radiation based X-ray fluorescence imaging approach

Recent studies have suggested that exposure of the freshwater invertebrate Daphnia magna to dietary Zn may selectively affect reproduction without an associated increase of whole body bioaccumulation of Zn. The aim of the current research was therefore to investigate the hypothesis that dietary Zn toxicity is the result of selective accumulation in tissues that are directly involved in reproduction. Since under field conditions simultaneous exposure to both waterborne and dietary Zn is likely to occur, it was also tested if accumulation and toxicity under combined waterborne and dietary Zn exposure is the result of interactive effects. To this purpose, D. magna was exposed during a 16-day reproduction assay to Zn following a 5 × 2 factorial design, comprising five waterborne concentrations (12, 65, 137, 207, and 281 μg Zn/L) and two dietary Zn levels (49.6 and 495.9 μg Zn/g dry wt.). Tissue-specific Zn distribution was quantified by synchrotron radiation based confocal X-ray fluorescence (XRF). It was observed that the occurrence of reproductive inhibition due to increasing waterborne Zn exposure (from 65 μg/L to 281 μg/L) was accompanied by a relative increase of the Zn burdens which was similar in all tissues considered (i.e., the carapax, eggs, thoracic appendages with gills and the cluster comprising gut epithelium, storage cells and ovaries). In contrast, the impairment of reproduction during dietary Zn exposure was accompanied by a clearly discernible Zn accumulation in the eggs only (at 65 μg/L of waterborne Zn). During simultaneous exposure, bioaccumulation and toxicity were the result of interaction, which implies that the tissue-specific bioaccumulation and toxicity following dietary Zn exposure are dependent on the Zn concentration in the water. Our findings emphasize that (i) effects of dietary Zn exposure should preferably not be investigated in isolation from waterborne Zn exposure, and that (ii) XRF enabled us to provide possible links between tissue-specific bioaccumulation and reproductive effects of Zn.

Trace-element analysis of individual synthetic and natural fluid inclusions with synchrotron radiation XRF using Monte Carlo simulations for quantification

The trace element composition of individual fluid inclusions was investigated by using synchrotron radiation X-ray fluorescence for analysis and Monte Carlo simulations for quantification. To validate the input parameters of the Monte Carlo simulation code for the applied spectrometer, area scan measurements on synthetic standard reference glasses (NIST 612 and NIST 610) were performed. Results yielded an accuracy of generally better than 20 % for all elements with Z between 37 and 92 at a standard deviation of less than 7 %. The analytical procedure was then applied to synthetic inclusions in quartz: single point analysis yielded an accuracy between 10 and 30 % with a reproducibility of ± 20 % and a repeatability of ± 7 % for the elements Cu, Rb, Sn and Cs. Ten trace elements (Mn, Fe, Cu, Zn, As, Rb, Nb, Sn, Sb, Cs) with concentrations between 2 and 10500 ppm were determined in fluid inclusions of hydrothermal quartz hosts from the Ehrenfriedersdorf Complex, Germany. Inclusions of three evolutionary stages of the Ehrenfriedersdorf Complex were studied. Vapour-rich inclusions of the pegmatite stage have low concentrations of all elements with Z > 20. Inclusions of the hydrothermal stage record progressive enrichment and differentia- tion in trace elements. Fluids of the early hydrothermal stage are enriched in Sn, Cu and As. Subsequently, they evolve to Fe-, Mn-, Zn- and Cs-rich fluids.

Trace element diffusion in rhyolitic melts comparison between synchrotron radiation X-ray fluorescence microanalysis (μ-SRXRF) and secondary ion mass spectrometry (SIMS)

Two microbeam techniques, synchrotron radiation X-ray fluorescence micro-analysis (μ-SRXRF) and secondary ion mass spectrometry (SIMS) are compared for analyzing diffusion profiles of trace elements in two hydrous rhyolitic glasses (1.87 and 5.00wt% H 2 O). In order to verify the results, laser ablation coupled to inductively coupled plasma optical emission (LA-ICP-OES) has been used on one sample. Samples were produced by diffusion couple experiments performed in an internally heated gas pressure vessel at 1200 °C and 500MPa. One half of each couple was doped with 24 trace elements representing different geochemical groups: low field strength elements (Rb, Sr, Ba), transition metals (Cr, Co, Ni, Cu, Zn), rare earth elements (La, Ce, Nd, Sm, Eu, Gd, Er, Yb) + Y, high field strength elements (V, Zr, Nb, Hf, Ta) and main group elements (Ge, Sn). Several profiles were measured with both μ-SRXRF and SIMS on both samples. In principle, concentrations of all elements can be extracted simultaneously from a single SRXRF spectrum. However, some trace elements could not be reliably quantified with our analytical system: Ta and Pb (used for detector collimator material), Ti, V (low energy of K α ), Co (K α -peak overlapping with Fe K β -peak) and Cr, Ni, Cu, Zn (overlapping with 1-lines of REEs). In contrast, SIMS analyses measure each element sequentially. Hence, not all elements of the large total set of trace elements could be analyzed in a single run. Some elements requiring a high mass resolution (NaSi interfering with V, CaO interfering with Ni) or having low yields (Sn) were not profiled. Multiple diffusivities derived from μ-SRXRF and SIMS profiles are in very good agreement for most elements. In general, the trace element diffusivity decreases with increasing valence state, e.g. in sample D22 containing 1.87wt% H 2 O from log D=-10.80 for the monovalent Rb to log D=-13.34 for the tetravalent Zr (Din m 2 /s). By increasing the water content in sample D18 to 5.00wt%, diffusion coefficients increase approximately by one order of magnitude for all elements studied.

Dual detection X-ray fluorescence cryotomography and mapping on the model organism Daphnia magna

Micro X-ray fluorescence (-XRF) is a rapidly evolving analytical technique which allows visualising the trace level metal distributions within a specimen in an essentially non-destructive manner. At second generation synchrotron radiation sources, detection limits at the sub-ppm level can be obtained with micrometer resolution, while at third generation sources the spatial resolution can be better than 100 nm. Consequently, the analysis of metals within biological systems using micro and nano X-ray fluorescence imaging is a quickly developing field of research. Since X-ray fluorescence is a scanning technique, the elemental distribution within the sample should not change during analysis. Biological samples pose challenges in this context due to their high water content. A dehydration procedure is commonly used for sample preparation, enabling an analysis of the sample under ambient temperature conditions. Unfortunately, a potential change of elemental redistribution during the sample preparation is difficult to verify experimentally and therefore can not be excluded completely. Creating a cryogenic sample environment allowing an analysis of the sample under cryogenic condition is an attractive alternative, but not available on a routine basis. In this article, we make a comparison between the elemental distributions obtained by micro SR-XRF within a chemically fixed and a cryogenically frozen Daphnia magna, a model organism to study the environmental impact of metals. In what follows, we explore the potential of a dual detector set-up for investigating a full ecotoxicological experiment. Next to conventional 2D analysis, dual detector X-ray fluorescence cryotomography is illustrated and the potential of its coupling with laboratory absorption micro-CT for investigating the tissue specific elemental distributions within this model organism is highlighted.

Trace element diffusion and element partitioning between garnet and andesite melt using synchrotron X-ray fluorescence microanalysis (μ-SRXRF)

Synchrotron radiation X-ray fluorescence microanalysis (μ-SRXRF) was applied to products of experimental geochemistry to determine (1) trace element diffusivities in andesite melts and (2) trace element partitioning behaviour between garnet and melt. To achieve sufficient spatial resolution, non-focusing and focusing glass capillaries reduced the incoming synchrotron beam down to sizes of 20 and 2.7 μm, respectively. (1) Diffusion couples of trace element-doped and undoped andesite melts were prepared in internally heated pressure vessels. A special sample setup allowed the pencil-shaped synchrotron beam to irradiate volume elements showing identical diffusion behaviour. Eighteen trace elements were measured simultaneously and quickly, resulting in diffusion profiles well suited for evaluating diffusion coefficients. (2) Garnet and andesitic melt were synthesized and equilibrated in a piston cylinder apparatus. The garnets were exceptionally large due to specially designed dehydration-melting experiments with monazite as a trace element source. Coexisting garnets and melt were analyzed with μ-SRXRF, and new distribution coefficients for Sr (0.126), Y (5.27), Zr (0.533), La (0.014), Ce (0.020), Nd (0.245), Sm (1.21), Eu (1.18), Gd (5.29), Yb (52.5), and Lu (76) were determined. However, the general use of μ-SRXRF for experimental partitioning studies is limited due to the relatively poor spatial resolution caused by the penetrating character of the synchrotron beam and due to limited count rates at high energies.