A. Simionovici

Mineralogy and Petrology of Comet 81P/Wild 2 Nucleus Samples

The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.

Elemental compositions of comet 81P/Wild 2 samples collected by Stardust

We measured the elemental compositions of material from 23 particles in aerogel and from residue in seven craters in aluminum foil that was collected during passage of the Stardust spacecraft through the coma of comet 81P/Wild 2. These particles are chemically heterogeneous at the largest size scale analyzed (∼180 ng). The mean elemental composition of this Wild 2 material is consistent with the CI meteorite composition, which is thought to represent the bulk composition of the solar system, for the elements Mg, Si, Mn, Fe, and Ni to 35%, and for Ca and Ti to 60%. The elements Cu, Zn, and Ga appear enriched in this Wild 2 material, which suggests that the CI meteorites may not represent the solar system composition for these moderately volatile minor elements.

Nanofocusing parabolic refractive X-ray lenses

Parabolic refractive x-ray lenses with short focal distance can generate intensive hard x-ray microbeams with lateral extensions in the 100 nm range even at a short distance from a synchrotron radiation source. We have fabricated planar parabolic lenses made of silicon that have a focal distance in the range of a few millimeters at hard x-ray energies. In a crossed geometry, two lenses were used to generate a microbeam with a lateral size of 380 nm by 210 nm at 25 keV in a distance of 42 m from the synchrotron radiation source. Using diamond as the lens material, microbeams with a lateral size down to 20 nm and below are conceivable in the energy range from 10 to 100 keV.

Synchrotron X-ray micro-beam studies of ancient Egyptian make-up

Abstract Vases full of make-up are most often present in the burial furniture of Egyptian tombs dated from the pharaonic period. The powdered cosmetics made of isolated grains are analysed to identify their trace element signature. From this signature we identify the provenance of the mineral ingredients in the make-up and we observe different impurities in products, which have been demonstrated as synthetic substances by previous works. Focused X-ray micro-beam ( 2×5 μm 2 ) is successively tuned at 11 keV, below the LIII absorption edge of Pb, and 31.8 keV for global characterisation of the metal impurities. The fluorescence signal integrated over each single grain is detected against the X-ray micro-diffraction pattern collected in transmission with a bi-dimensional detector. Furthermore, for galena grains rich in Zn, the XANES signal at the K-absorption edge of Zn shows its immediate nearest-neighbour environment.

Parabolic refractive X-ray lenses: a breakthrough in X-ray optics

Refractive X-ray lenses, considered for a long time as unfeasible, have been realized with a rotational parabolic profile at our institute: The main features of the new lenses are: they focus in two directions and are free of spherical aberration. By varying the number of individual lenses in the stack the focal length can be chosen in a typical range from 0.5 to 2 m for photon energies between about 6 and 60 keV. The aperture of the lens is about 1 mm matching the angular divergence of undulator beams at 3d generation synchrotron radiation sources. They cope without problems with the heat load from the white beam of an undulator. Finally, they are easy to align and to operate. Refractive X-ray lenses can be used with hard X-rays in the same way as glass lenses can be used for visible light, if it is taken into account that the numerical aperture is small (of the order 10 � 4 ). Being high-quality optical elements, the refractive X-ray lenses can be used for generating a focal spot in the mm range with a gain of a factor 1000 and more, or for imaging purposes as in a hard X-ray microscope. Recent examples from microanalysis, microtomography, fluorescence tomography, X-ray microscopy will be shown to demonstrate the state of the art. Possible new developments will be discussed. # 2001 Elsevier Science B.V. All rights reserved. PACS: 41.50; 07.85.T

A new nondestructive X-ray method for the determination of the 3D mineralogy at the micrometer scale

Abstract The combination of synchrotron-based X-ray absorption and fluorescence computed tomographies (CT) is a new method allowing a noninvasive and nondestructive determination of the three-dimensional (3D) mineralogy with micrometer resolution of sub-millimeter silicate grains, possibly stored in a silica holder. These CT were performed with beams of a few tens of keV from a third-generation synchrotron source on one olivine grain of the NWA817 Martian meteorite presenting a reddish alteration phase. The reconstructed sections show a network of fractures and a few micrometer-thick layers formed on one grain. The 3D facet orientation and the X-ray attenuation coefficient indicate that this grain is an Fo44±9 olivine crystal. The fluorescence section reveals rims enriched in Fe (a major element) or depleted in Ca (a minor element). This CT combination shows that the micrometer-thick layer is preferentially formed on the (010) olivine face and has a lower density (3.5 ± 0.4 g/cm3 ) than the olivine, even though it is enriched in Fe. Its complex nano-petrography and the distributions of nanometer-sized voids and fractures in such a micrometer thick layer, first observed by scanning electron microscopy on focused ion-beam cuts, is not shown by CT. The precision presently achieved, although moderate, is sufficient to obtain a 3D semi-quantitative view of the mineralogy consistent with the one previously established by electron probe microanalyses (Sautter et al. 2002).

Iron distribution in cancer cells following doxorubicin exposure using proton and X-ray synchrotron radiation microprobes

Chemical studies have shown that doxorubicin, a well-established anticancer agent, is a powerful iron chelator and the resultant iron - drug complex is an efficient catalyst of the conversion of hydrogen peroxide to the highly reactive hydroxyl radical. However, the intracellular complexation of doxorubicin with iron is still debated. Using nuclear microprobe analysis (NMPA), we previously observed in human ovarian cancer cells exposed to 20 μM iodo-doxorubicin (IDX) that iodine and iron cellular distributions were spatially correlated, suggesting a mechanism of intracellular iron chelation by the anthracycline compound. Because maximal plasma drug concentrations in patients are expected to be around 5 μM, NMPA and X-ray absorption near edge spectroscopy (XANES) experiments for iron speciation analysis were performed on cultured cells exposed to pharmacological doses of 2 μM IDX or doxorubicin.

In situ mapping of high-pressure fluids using hydrothermal diamond anvil cells

We present new results combining high pressures and temperatures attainable in a diamond anvil cell with in situ synchrotron radiation induced micro-X-ray fluorescence measurements. Hydrothermal diamond anvil cells experiments have been performed by measuring the partitioning of Pb between aqueous fluids (pure water or NaCl-enriched water) and hydrous silicate melts of haplogranite composition using synchrotron X-ray fluorescence. The in situ measurements were performed in the range 0.3–1.2 GPa and 730–850 °C both in the aqueous fluid and in the silicate melts being in equilibrium. Pb is strongly partitioned into high-pressure–temperature hydrous melts when Cl is present in either the hydrous melt or the aqueous fluid. Moreover, our comparisons of in situ results with post-mortem results show that significant changes take place during rapid quenching especially when samples are small (few hundred of microns in diameter). Water exsolution is induced by the quench in the silicate melt showing the high mobility of Pb which immediately partitions into the water vapor phase during the quench. The current in situ approach offers thus a pertinent complementary method to the classical experimental petrology investigations.

Instrumental development of X-ray atomic holography at ESRF

Abstract We have developed an X-ray Fluorescence Holography (XFH) setup at the European Synchrotron Radiation Facility (ESRF). The main difficulty inherent to XFH is that the holographic signal is in the low 10 −3 range compared to the background isotropic fluorescent radiation. This requires a very pure fluorescent signal and the highest possible count rate. Therefore, we designed a focusing analyser system with large solid angle acceptance. The photons of the focused beam were counted by an avalanche photodiode in single-photon counting mode up to a few MHz. At even higher intensity, we switched to a Si diode working in the photocurrent mode. Due to the relatively weak requirements on the bandwidth of the exciting incident radiation, we could directly use the undulator beam, discriminating lower harmonics by an absorber and higher ones by reflecting the beam on a Si mirror. By developing a fast, continuous “spiral” scanning technique, a full hologram could be recorded in 30xa0sec.

Non-destructive search for interstellar dust using synchrotron microprobes

Here we describe the critical role that synchrotron X-ray and infrared microprobes are playing in the search for interstellar dust in the Stardust Interstellar Dust Collector (SIDC). The samples under examination are submicron particles trapped in low-density aerogel. We have found that the spatial resolution, energy range, and flux capabilities of the FTIR beamlines 1.4.3, ALS, and U2B, NSLS; the XRF microprobes ID13 and ID22NI, ESRF and 2-ID-D, APS; and the STXM beamline 11.0.2, ALS are ideally suited for studying these tiny returned samples. Using nondestructive, coordinated analyses at these microprobes, we have been able to eliminate most candidates as likely samples of interstellar dust. This in itself is a major accomplishment, since the analysis of these tiny samples is technically extremely challenging.