Statistics – Computation
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmmb52a..03e&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #MB52A-03
Statistics
Computation
6040 Origin And Evolution, 6240 Meteorites And Tektites (1028, 3662), 6982 Tomography And Imaging (7270, 8180), 1028 Composition Of Meteorites (3662, 6240), 1094 Instruments And Techniques
Scientific paper
X-ray computed microtomography allows 3D analysis of the density structure of small samples, prior to sectioning. This is particularly useful for rare samples such as carbonaceous chondrites and their components, Martian meteorites, and samples returned by space missions. The Advanced Photon Source provides high-brightness x-rays yielding high quality images at resolutions of 1 to 20 microns per volume element (voxel) edge. Advances in the last year at APS-GeoCARS allow much faster imaging, sharper contrast, and reduced noise. Results are 12-bit grayscale values for x-ray attenuation at each voxel, suitable for image analysis, or display as movies. In chondritic meteorites, components of interest can be located in whole rock samples; melilite can be distinguished from pyroxene in Ca-Al-rich inclusions (CAIs); void spaces can be characterized prior to sectioning; metal grain locations and abundances can be accurately assessed; and size, shape and frequency statistics for chondrules determined. Crystal core-rim relations in Martian cumulates can be resolved due to FeO zoning. Potential melt-inclusion-bearing phenocrysts can be efficiently located in lunar fire-fountain glass spherules. Aerogel analogs to Stardust mission tiles (20mm x 40mm x 30mm deep) impacted by dust can be searched using tomography, before destructive cutting. Because the field of view for a typical CCD does not allow high-resolution imaging of a whole sample, we have developed and tested a new 'lambda tomography' technique to image sequential adjacent volumes, with rotation centers on a close-packed grid. Combining volumes, and whole-volume analysis are computationally challenging, given the ca. 500MB size of a single data volume. Calculated sample heating is negligible even for multiple scans of aerogel with very low thermal conductivity. Rotation of a large portion of low-attenuation aerogel tile outside the field of view has little effect on reconstruction of the voxel x-ray attenuation in the field. We have also applied 'lambda tomography' with success to adjacent rotation centers in meteorite (rock) samples, where sample density limits absolute size in the x-ray beam.
Ebel Denton S.
Rivers Mark L.
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