ALS Users Meeting 19-Oct-2004 GSECARS X-ray Microprobe for Earth and Environmental Sciences Matthew Newville, Peter Eng, Steve Sutton, Mark Rivers Consortium for Advanced Radiation Sources (CARS) University of Chicago, Chicago, IL X-ray Absorption (XANES / EXAFS) Objectives for Earth and Environmental Sciences: X-ray microprobe techniques: oxidation state of selected element near-neighbor distances and coordination numbers abundance and spatial correlations of heavy elements X-ray Fluorescence (XRF), Fluorescence Mapping Determine chemical associations, speciation, and structure of heavy elements on heterogeneous samples: soils, sediments, aggregates, plant material, isolated inclusions, or contaminants. X-ray Micro-diffraction phase identification

ALS Users Meeting 19-Oct-2004 Focusing: Kirkpatrick-Baez mirrors: Rh- coated Si, typically using 3x3  m spot sizes, at 50mm from end of mirrors. Incident Beam: LN 2 cooled Si (111) mono Sample Stage: x-y-z stage, 1  m resolution Fluorescence detector: 16-element Ge detector with DXP electronics Si-drift detector (shown) Lytle Detector Wavelength Dispersive Spectrometer Optical Microscope: 5x to 50x objective with external video system. GSECARS microprobe: APS 13-ID Entrance Slits: typically 250  m, accepting ~30% of undulator beam CCD Camera: Bruker 2k area detector

ALS Users Meeting 19-Oct-2004 The table-top Kirkpatrick-Baez mirrors use four-point benders and flat, trapezoidal mirrors to dynamically form an ellipsis. They can focus a 300x300  m beam to 1x1  m. With a typical working distance of 100mm, and a focal distance and spot-size independent of energy, they are ideal for micro-XRF and micro-EXAFS. We use Rh-coated silicon for horizontal and vertical mirrors to routinely produce 2x3  m beams for XRF, XANES, and EXAFS. Kirkpatrick-Baez Focusing Mirrors

ALS Users Meeting 19-Oct-2004 Nicole Keon, Daniel Brabander, Harold Hemond (MIT), GSECARS The Superfund site at the Wells G+H wetland, Woburn, MA (featured in A Civil Action) contains ~10 tons of arsenic within the upper 50 cm of the sediment. Most of the arsenic is held in the wetland sediments with relatively little As in the groundwater. Usually an iron-reducing, anoxic environment such as a sediment would be expected to have high As mobility. Can the metabolic activity of wetland plants, such as Typha latifolia (cattail) explain the sequestration of arsenic in the wetland? Within ~100  m of the roots, Fe is oxidized to Fe(III) and forms a plaque on the root, even in these sediments. Could As be adsorbed to the ferric oxy- hydroxides formed at the root exteriors? Where is As in the cattail roots? What elements (Fe) are associated with As? What is the As oxidation state in the roots? Arsenic/Iron in cattail roots: XRF tomography Physical slicing the root for 2D XRF mapping would damage the sample. Fluorescence tomography can make a virtual slice of the root and show the elemental associations and concentrations in the slice. AsFe ZnCu

ALS Users Meeting 19-Oct-2004 X-ray computed microtomography (CMT) gives 3D images of the x-ray absorption coefficient. An absorption image is collected as the angle  is rotated through 180 o, and the 3D image is reconstructed in software. In some cases, element-specific images can be made by tuning the x-ray energy above and below an absorption edge. Fluorescence x-ray tomography use a focused beam, scanned across the sample. The sample is rotated around  and translated in x. Fluorescence x-rays are collected as for XRF maps. Transmission x-rays are measured as well to give an overall density tomograph. data collection is relatively slow – one slice can be made at a time. can be complicated by self-absorption. can collect multiple fluorescence lines. X-ray Fluorescence Tomography: Primer broad x-ray beam rotation stage Sample Phosphor CCD camera  fluorescence detector Transmission detector x visible light focused x-ray beam Sample  rotation and translation stages fluoresced x-rays

ALS Users Meeting 19-Oct-2004 Fluorescence detector: multi-element Ge detector Sample stage: x-y-z-  Sample, mounted on silica fiber, or in ‘shrink-wrap’ tube, on a goniometer head KB mirrors, with Pb tape shield Fluorescence Tomography: Experimental Setup Optical microscope

ALS Users Meeting 19-Oct-2004 x  The raw fluorescence tomography data consists of elemental fluorescence (uncorrected for self-absorption) as a function of position and angle: a sinogram. This data is reconstructed as a virtual slice through the sample by a coordinate transformation of (x,  )  (x, y). The process can be repeated at different z positions to give three-dimensional information. Fluorescence sinograms collected simultaneously for Zn, Fe, and As for a cross-section of As-contaminated cattail root (photo, right): x: 1100  m in 10  m steps  : 180  in 3  steps Fluorescence Tomography: Sinograms Zn FeAs

ALS Users Meeting 19-Oct-2004 Wells G&H Typha latifolia root: reconstructed slices from fluorescence  -tomography, showing As concentrated on the root exterior, associated with Fe. Fluorescence Tomogram Slices of Cattail Roots AsFe ZnCu Quantitative XRF analysis of the As and Fe concentrations from these slices give an As/Fe molar ratio of ~10 ppm, consistent with the average from bulk, wet chemical techniques. Though only a few virtual slices could be made, this gives us confidence that the slices made are representative of the average. As and Fe are both at root plaque, not in the root interior. As and Fe are ~98% correlated. Cu, Zn, and Pb (not shown) are less uniform on plaque, suggesting they are not co-precipitated with or sorbed onto the Fe phase. Bulk XAFS of Fe shows Fe(III).

ALS Users Meeting 19-Oct-2004 As XANES XANES measurements on the Typha latifolia cattail roots show mixed As oxidation state. The As 3+ fraction did vary between different root samples, and along a single root, ranging from ~10% to ~60% As 3+. The spectra here shows roughly equal portions As 3+ and As 5+, which is higher As 3+ than average. Porewaters in the wetland have ~50% As 3+ : the As is generally more oxidized in the root plaque, which is consistent with adsorption onto ferric oxyhydroxides.

ALS Users Meeting 19-Oct-2004 As XANES, Oxidation State Tomograms Fluorescence tomograms made at 2 different energies: E As total As concentration E As 3+ As 3+ concentration would show spatial dependence of the As oxidation state. XANES measurements on the Typha latifolia cattail roots show mixed As oxidation state. The As 3+ fraction did vary between different root samples, and along a single root, ranging from ~10% to ~60% As 3+. The spectra here shows roughly equal portions As 3+ and As 5+, which is higher As 3+ than average.

ALS Users Meeting 19-Oct-2004 The As 3+ / As ratio is heterogeneous (boxed areas). As 5+ appears correlated with metals (Fe, Cu, Zn). There does not seem to be a systematic spatial As oxidation gradient. As oxidation tomograms for Cattail Roots As 3+ As total As 3+ total As 5+ appears at location with high Cu and Zn. As 5+ appears at location with high Fe. More detailed spatial and oxidation state information would need faster data collection rates. N. Keon, et al., Environ Sci & Tech, Oct 2004 (on line already….).

ALS Users Meeting 19-Oct-2004 Ni in hyperaccumulating Alyssum murale David H. McNear Jr*, Edward Peltier, Univ of Delaware

ALS Users Meeting 19-Oct-2004 Ken Severin, Tom Trainor, Univ of Alaska, Fairbanks, Randy Brown, US Fish and Wildlife Service Sr distribution in Artic fish ear bones One promising approach is to study the composition of otoliths (ear bones) which are records of the water chemistry. Sr is particularly interesting, as it seems to be strongly correlated with salinity, and can be incorporated directly into the carbonate phases. Bulk XRD shows a mixture of vaterite and aragonite. Thin section of sheefish otolith: the dark inclusion is presumed to be vaterite while the lighter area expected to be aragonite. The otoliths are ~96% CaCO 3 (mostly aragonite) and ~4% protein. Electron microprobe results: strong Sr heterogeneity, consistent with aragonite / vaterite (aragonite can incorporate more Sr). Artic migratory fish, such as sheefish (stenodus leucicthys), are difficult to track, which complicates fisheries management. For the sheefish, it is not even known how much time is spent in fresh and brackish waters. (Sheefish from the Selawik river in northern Alaska). One promising approach is to study the composition of otoliths (ear bones) which are records of the water chemistry. Sr is particularly interesting, as it seems to be strongly correlated with salinity, and can be incorporated directly into the carbonate phases. Bulk XRD shows a mixture of vaterite and aragonite.

ALS Users Meeting 19-Oct-2004 We start with XRF analysis: A line scan (a 1-dimensional map) shows a strong variation in Sr concentration (from ~2000ppm down to ~200ppm), across the aragonite (high Sr) to vaterite (low Sr) regions. There is a strong heterogeneity in Zn (at 10s of ppm level), while Cr, Mn, Fe, Co, and Ni are uniformly distributed across the section. We then proceed to doing XAFS on selected spots (#1: high Sr and #2: low Sr / high Zn). Sr distribution in Selawik Sheefish otoliths Ken Severin, Tom Trainor, Univ of Alaska, Fairbanks, Randy Brown, US Fish and Wildlife Service

ALS Users Meeting 19-Oct-2004  XAFS (with ~10x10  m spot size) were collected on selected spots: #1: high Sr #2: low Sr / high Zn Also shown is data from Sr in coral aragonite from Allison et al. (earlier GSECARS  XAFS measurements). Sheefish Sr micro-XAFS Spot #2Spot #1 EXAFS analysis in progress…. Ken Severin, Tom Trainor, Univ of Alaska, Fairbanks, Randy Brown, US Fish and Wildlife Service

ALS Users Meeting 19-Oct-2004 Sheefish Sr micro-XRD Spot #2Spot #1Spot #7  XRD (with ~10x10  m spot size) were collected on several spots. Spots #1 and #7 are confirmed to be aragonite and vaterite structures, but there are questions about spot #2 (high Zn). More work needed, but a good start for 2 days of beam time. Ken Severin, Tom Trainor, Univ of Alaska, Fairbanks, Randy Brown, US Fish and Wildlife Service

ALS Users Meeting 19-Oct-2004 Conclusions, Future Directions and Improvements The GSECARS microprobe station is running well and productively, combining  XRF, mapping, tomography,  XRF, XANES, and EXAFS for a wide range of problems in geological, soil, and environmental sciences. Areas for Improvement: Beam positional stability, especially during EXAFS. This has improved, but needs more work. Ease of focus to below 2  m and of reliable defocus / refocus to a desired beam size. Data collection speed and efficiency. We’re generally limited in time by the solid-state fluorescence detectors. Ease of use for novice users: data collection and on-line analysis software for quantitative XRF, XANES, EXAFS, and XRD.