Optimizing pink-beam fast X-ray microtomography for multiphase flow in 3D porous media.

A fast pink-beam X-ray microtomography methodology was developed at the GSECARS 13-BMD beamline at the Advanced Photon Source to study multiphase flow in porous media. The white beam X-ray distribution of the Advanced Photon Source is modified using a 1-mm copper filter and the beam is reflected off a platinum mirror angled at 1.5 mrad, resulting in a pink beam with X-ray intensities predominately in the range of 40-60 keV. Bubble formation in the wetting phase and wettability alteration of the solid phase from x-ray exposure can be a problem with high flux and high energy beams, but the suggested pink-beam configuration mitigates these effects. With a 14-second acquisition time for capturing a complete dataset, the evolving fluid-fronts of nonequilibrium three-dimensional multiphase flow can be studied in real-time and the images contain adequate image contrast and quality to measure important multiphase quantities such as contact angles and interfacial areas. LAY DESCRIPTION: Understanding how fluids are transported through porous materials is pertinent to many important societal processes in the environment (e.g. groundwater flow for drinking water) and industry (e.g. drying of industrial materials such as pulp and paper). To develop accurate models and theories of this fluid transportation, experiments need to track fluids in 3-dimensions quickly. This is difficult to do as most materials are opaque and therefore cameras cannot capture fluid movement directly. But, with the help of x-rays, scientists can track fluids in 3D using an imaging technique called x-ray microtomography (µCT). Standard µCT takes about 15 minutes for one image which can produce blurry images if fluids are flowing quickly through the material. We present a technique, fast µCT, which uses a larger spectrum of x-rays than the standard technique and acquires a 3D image in 14 seconds. With the large amount of x-rays utilized in this technique, bubbles can start to form in the fluids from x-ray exposure. We optimized the utilized x-ray spectrum to limit bubble formation while still achieving a rapid 3D image acquisition that has adequate image quality and contrast. With this technique, scientists can study fluid transport in 3D porous materials in near real-time for the improvement of models used to ensure public and environmental health.

Hyperaccumulator Alyssum murale relies on a different metal storage mechanism for cobalt than for nickel.

The nickel (Ni) hyperaccumulator Alyssum murale has been developed as a commercial crop for phytoremediation/phytomining Ni from metal-enriched soils. Here, metal co-tolerance, accumulation and localization were investigated for A. murale exposed to metal co-contaminants. A. murale was irrigated with Ni-enriched nutrient solutions containing basal or elevated concentrations of cobalt (Co) or zinc (Zn). Metal localization and elemental associations were investigated in situ with synchrotron X-ray microfluorescence (SXRF) and computed-microtomography (CMT). A. murale hyperaccumulated Ni and Co (> 1000 microg g(-1) dry weight) from mixed-metal systems. Zinc was not hyperaccumulated. Elevated Co or Zn concentrations did not alter Ni accumulation or localization. SXRF images showed uniform Ni distribution in leaves and preferential localization of Co near leaf tips/margins. CMT images revealed that leaf epidermal tissue was enriched with Ni but devoid of Co, that Co was localized in the apoplasm of leaf ground tissue and that Co was sequestered on leaf surfaces near the tips/margins. Cobalt-rich mineral precipitate(s) form on leaves of Co-treated A. murale. Specialized biochemical processes linked with Ni (hyper)tolerance in A. murale do not confer (hyper)tolerance to Co. A. murale relies on a different metal storage mechanism for Co (exocellular sequestration) than for Ni (vacuolar sequestration).

Elemental Distributions in Marine Bivalve Shells as Measured by Synchrotron X-Ray Fluorescence.

The concentrations of elements from Mn to Pb in the shells of Mercenaria mercenaria, Mya arenaria, and Argopecten irradians were measured using synchrotron x-ray fluorescence. This technique provides sensitivity as low as 1 ppm and resolution of 8 {mu}m. Elements were heterogeneously distributed, both on a large scale (several millimeters) and on a small scale (tens of micrometers). Large-scale variations were observed in the compositions of shell layers and in seasonal variations in strontium concentration. Small-scale changes in composition included elevated iron levels at the boundary between the prismatic and inner homogeneous shell of the hard clam, Mercenaria mercenaria. Variations in strontium concentrations were seen over time spans of several months, suggesting that this technique can be used to determine historical water temperatures. Elemental maps with a resolution of less than 10 {mu}m were produced.

Evidence for extreme partitioning of copper into a magmatic vapor phase.

The discovery of copper sulfides in carbon dioxide- and chlorine-bearing bubbles in phenocryst-hosted melt inclusions shows that copper resides in a vapor phase in some shallow magma chambers. Copper is several hundred times more concentrated in magmatic vapor than in coexisting pantellerite melt. The volatile behavior of copper should be considered when modeling the volcanogenic contribution of metals to the atmosphere and may be important in the formation of copper porphyry ore deposits.

An X-ray microprobe facility using synchrotron radiation.

An X-ray microprobe for trace elemental analysis at micrometer spatial resolutions, using synchrotron radiation (SR), is under development. The facility consists of two beamlines, one including a 1:1 focusing mirror and the other an 8:1 ellipsoidal mirror. At present, "white light" is used for excitation of the characteristic X-ray fluorescence lines. Sensitivities in thin biological samples are in the range of 2-20 fg in 100 microns2 areas in 5 min irradiation times. Scanning techniques, as well as microtomography and chemical speciation, are discussed. Application to a specific biomedical study is included.