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Komatiites are volcanic rocks mainly of Archaean age that formed by unusually high degrees of melting of mantle peridotite. Their origin is controversial and has been attributed to either anhydrous [...]

X-ray fluorescence computed tomography (XFCT) is a synchrotron-based imaging modality employed for mapping the distribution of elements within slices or volumes of intact specimens. A pencil beam of external radiation is used to stimulate emission of characteristic X-rays from within a sample, which is scanned and rotated through the pencil beam in a first-generation tomographic geometry. The measurements so obtained can be represented as generalizations of the attenuated Radon Transform. The range of angular scanning employed is the subject of some variability in the XFCT imaging community, as some groups rotate the object through a full 360[degrees], while others employ only a 180[degrees] rotation. In both cases, the entire object is scanned through the beam at each projection view. The use of a 180[degrees] rotation is sometimes justified by implicit reference to a well-known symmetry property of the Radon transform, but that symmetry does not hold for the attenuated Radon transform. In this work, we demonstrate that a full scan of the object at each view coupled with a 360[degrees] rotation does contain a two-fold data redundancy. While the redundancy does not give rise to a simple symmetry condition as in the case of the Radon transform, we will show that it does indeed license the use of the 180[degrees] scheme. However, we will also demonstrate that when there is a single external fluorescence detector, the redundancy also licenses a potentially more attractive reduced-scan scheme, in which the object is rotated through a full 360[degrees], but in which only the half of the object closest to the fluorescence detector is scanned at each projection view. This new scheme may permit both reduced imaging times and improved image quality. Index Terms--Image reconstruction, penalized-likelihood methods, X-ray fluorescence computed tomography.

Cu K-edge X-ray absorption near edge structure (XANES) spectra were recorded from individual synthetic brine fluid inclusions as a function of temperature up to 500 [degrees]C. The inclusions serve as sample cells for high-temperature spectroscopic studies of aqueous Cu-Cl speciation. [Cu.sup.+] and [Cu.sup.2+] can both be identified from characteristic pre-edge features. Mixed oxidation states can be deconvoluted using linear combinations of [Cu.sup.+] and [Cu.sup.2+] spectra. This work illustrates how complex Cu XANES spectra can be interpreted successfully. [Cu.sup.2+] is the stable oxidation state in solution at room temperature and [Cu.sup.+] at high temperatures. The change in oxidation state with temperature was completely reversible. [Cu.sup.+] was found to occur exclusively as the linear species [[Cu[Cl.sub.2]].sup.-] in solutions containing KCl with Cu:Cl ratios up to 1:6. In the absence of [K.sup.+], there is evidence for higher order coordination of [Cu.sup.+], in particular the tetrahedral complex [[Cu[Cl.sub.4].sup.3-]. The importance of such complexes in natural ore-forming fluids is yet to be determined, but may explain the vapor-phase partitioning of Cu as a Cl complex from a Cl-rich brine. Keywords: XAS (XAFS, XANES), Cu in high-temperature brines, high-temperature studies, XANES of fluid inclusions, fluid phase, experimental petrology, synthetic fluid inclusions

A new method has been developed to orient 50-100 [micro]m size single crystals to obtain XANES or EXAFS spectra along any crystallographic orientation relative to a polarized synchrotron X-ray beam. The method uses a modified spindle stage and an X-ray goniometer head to hold a crystal and the glass fiber on which it is mounted. The orientation of the crystallographic axes within the crystal can be determined by X-ray diffraction in all cases or with the use of the polarizing light microscope if the minerals are biaxial. Once an optical orientation direction has been located, it can be oriented parallel to the polarization direction of the synchrotron source for spectral acquisition. Mineral samples representing the three optical classes (i.e., isotropic, uniaxial, and biaxial) were oriented along their a, b, and c crystallographic axes, and Fe-XANES spectra were obtained. In all cases the interactions of polarized X-rays with the crystal structures are analogous to the interactions of visible light (e.g., as represented by refractive index). For the isotropic almandine sample the XANES spectra were similar at all orientations. For the uniaxial buergerite and scapolite samples the spectra were similar along the a and b axes and different along c. A detailed set of spectra acquired at multiple (known) optical orientations in the scapolite crystal demonstrates that spectral features vary in intensity as a function of orientation, with maxima and minima when the X-rays are polarized along optical orientations. For the biaxial fayalite sample, the XANES spectra differed along all three crystallographic axes, as expected by analogy to optical properties.

X-ray fluorescence elemental maps and Cu K-edge X-ray absorption near-edge structure (XANES) spectra were recorded for individual vapor and brine phase fluid inclusions from the Mole Granite, NSW, Australia. The maps indicate that Cu is concentrated in the vapor inclusions and, at room temperature, distributed uniformly in the condensed liquid. Opaque precipitates in these inclusions do not contain Cu. The absorption spectra identify the stable complexes as [[[Cu([H.sub.2]O).sub.6]].sup.2+] at 25[degrees]C, [[Cu[Cl.sub.2]].sup.1-] at 200[degrees]C, and either [Cu[Cl.sub.2].sup.1-] or [CuCl([H.sub.2]O)] at the homogenization temperature of around 400[degrees]C. These changes in Cu coordination and oxidation state are fully reversible. We suggest that the vapor phase partitioning of Cu as a chloride complex from a high-density brine may occur under acidic conditions. Estmates of fluid acidity at the time of boiling may potentially predict the metal distribution between epithermal and porphyry-type environments in hydrothermal systems.

Two clay soil column samples are taken from Almeda County, California and exposed to chromium contamination. The diffusion and reduction of the chromium in the soils is measured using X-ray absorption near edge structure spectroscopy, and graphed for depth of transport.

Issues concerning the use of physicist's tools to enhance understanding of the properties of earth materials and earth processes are presented. Reference is made to the use of synchrotron radiation and neutron radiation.

The use of micro-X-ray absorption near-edge structure (micro-XANES) spectroscopy enabled a direct, in-situ, spatial and temporal resolution of the transport of selenium between the water-sediment boundary. Results showed that speciation governed selenium's movement from the water to the substrate, where Se(VI) was abstracted from the water and bonded to the substrate as Se(0).

Spatially resolved absorption spectroscopy (XAS) was used to study the in situ chemical speciation of uranium (U). Qualitative information on U-bonding environments, specific information on U oxidation states and information on associated elemental distributions were obtained. Knowledge of U speciation in soils and sediments would be useful in formulating remediation strategies for U-contaminated soils.

X-ray fluorescence microtomography is used for imaging the distribution of Pt drugs within multicellular tumour spheroids. Results show that there is no difference between the distributions of the range of Pt(II) and Pt(IV) complexes, indicating that the complexes that are more resistant to cellular uptake is required for ensuring complete distribution throughout a tumor.