Geert Silversmit

F-54 Stardust Cometary Matter Analyzed By Synchrotron Nano-XRF: New Results and Developments

Stardust is an interplanetary spacecraft launched on February 7, 1999, by NASA, whose primary purpose was to investigate the make up of comet Wild2 and its coma. A second goal of the project was the acquisition of interstellar dust. In order to facilitate the capture of the particles, the spacecraft was equipped with aerogel (highly porous silica foam with an extremely low density) collectors. After the return of Stardust to Earth on January 15, 2006, the acquired samples were distributed among more than 150 researchers worldwide, including the X-Ray Micro-spectroscopy and Imaging group of Ghent University (XMI-UGent). nEach presented sample contains an elongated cavity (called track) produced by the impact and deceleration of a single comet coma particle through the aerogel. Multiple experiments were performed on such tracks and their terminal particle at the ESRF ID13 beamline using several non-destructive X-ray based methods such as conventional 2D scanning nano X-ray fluorescence (XRF) and confocal nano-XRF imaging. The latter technique is applied by mounting a polycapillary half-lens in front of the energy dispersive detector, thereby effectively reducing the volume defined by the intersection of the incoming beam and the sample to a volume defined by the acceptance of the polycapillary. A linear Fresnel lens assembly or a KB-mirror system, were used to reduce the dimensions of the incoming X-ray beam to the 200-300 nm level. nThe recorded XRF data have been evaluated using XMI-quant, a software package made by the XMI-UGent group in order to perform quantitative evaluation of micro-XRF spectra with special focus on data from confocal XRF imaging experiments. This software package includes an implementation of the fundamental parameter method allowing the analysis of the complex Stardust particles. The presented quantitative results confirm the earlier findings concerning the presence of Ca-Al-rich inclusions in the cometary dust.

F-39 A TOP-DOWN APPROACH USING X-RAY IMAGING TECHNIQUES: INSTRUMENTAL DEVELOPMENTS AND APPLICATIONS IN LIFE SCIENCE

Synchrotron radiation X-ray fluorescence micro- and nanobeam techniques at second- and third generation SR sources offer the potential of non-destructive multi-element analysis down to trace concentration levels with unrivalled spatial resolution among X-ray based analytical techniques. At these sources, relative detection limits at the sub-ppm (fg/ng) level can be achieved. With respect to absolute detection limits (DL), sub-micron sized X-ray beams can offer DLs below 1 ag for the most efficiently excited transition elements, with a potential lateral resolution level better than 100 nm. n nThese characteristics of micro/nanobeam SR-XRF allow spatially resolved multi-element determination of major, minor and trace constituents in microscopic sub areas and volumes within biological specimens in an essentially non-destructive/non-invasive manner. However, the complexity of performing such an experiment is often quite considerable, involving dedicated sample preparation, transportation towards and experimenting at the synchrotron facility, installing an appropriate experimental set-up and performing a thorough data analysis on large amounts of spectral data. n nThe ecotoxicological research on Daphnia magna, a frequently used model organism for investigating the mechanisms of toxicity of metals, has often been difficult because many analytical techniques are not able to investigate trace metal distributions in a spatially resolved manner at a (sub)microscopic resolution. As illustrated by this presentation, SR-XRF microanalysis allows to fill this gap and moreover, due to the variety in sizes of X-ray beams available, this research can be performed from the organism level towards the tissue and cellular level, representing a top-down approach.