Geoscience applications of x-ray computed microtomography

A facility for x-ray computed microtomography (CMT) has been commissioned on the bending magnet beamline at the GeoSoilEnviroCARS sector at the Advanced Photon Source (APS). The APS bending magnet has a critical energy of 20 keV, and thus provides high flux at photon energies up to 100 keV, making it well suited to imaging a wide range of earth materials up to several cm in size. The current apparatus uses a Si (220) channel-cut monochromator covering the energy range from 5 to 35 keV with beam sizes up to 18mm wide and 4mm high. The transmitted x-rays are imaged with a single crystal YAG scintillator, a microscope objective and a 1242x1152 pixel fast CCD detector. The system spatial resolution is about 3 microns in both the transmission radiographs and the reconstructed slices; Data collection times are approximately 30 minutes. This facility has been used to conduct a number of preliminary studies of earth materials, including inclusion in diamonds, pores in waste repository rocks and fossils. Fluorescence tomography has been conducted on the companion undulator beamline, where we have imaged the internal trace element distribution in interplanetary dust particles.