D. P. Siddons

The X‐ray Fluorescence Microscopy Beamline at the Australian Synchrotron

A hard x‐ray micro‐nanoprobe has commenced operation at the Australian Synchrotron providing versatile x‐ray fluorescence microscopy across an incident energy range from 4 to 25 keV. Two x‐ray probes are used to collect μ‐XRF and μ‐XANES for elemental and chemical microanalysis: a Kirkpatrick‐Baez mirror microprobe for micron resolution studies and a Fresnel zone plate nanoprobe capable of 60‐nm resolution. Some unique aspects of the beamline design and operation are discussed. An advanced energy dispersive x‐ray fluorescence detection scheme named Maia has been developed for the beamline, which enables ultrafast x‐ray fluorescence microscopy.

The Maia Spectroscopy Detector System: Engineering for Integrated Pulse Capture, Low-Latency Scanning and Real-Time Processing

The Maia detector system is engineered for energy dispersive x‐ray fluorescence spectroscopy and elemental imaging at photon rates exceeding 107/s, integrated scanning of samples for pixel transit times as small as 50μs and high definition images of 108 pixels and real‐time processing of detected events for spectral deconvolution and online display of pure elemental images. The system developed by CSIRO and BNL combines a planar silicon 384 detector array, application‐specific integrated circuits for pulse shaping and peak detection and sampling and optical data transmission to an FPGA‐based pipelined, parallel processor. This paper describes the system and the underpinning engineering solutions.

The New Maia Detector System: Methods For High Definition Trace Element Imaging Of Natural Material

Motivated by the need for megapixel high definition trace element imaging to capture intricate detail in natural material, together with faster acquisition and improved counting statistics in elemental imaging, a large energy‐dispersive detector array called Maia has been developed by CSIRO and BNL for SXRF imaging on the XFM beamline at the Australian Synchrotron. A 96 detector prototype demonstrated the capacity of the system for real‐time deconvolution of complex spectral data using an embedded implementation of the Dynamic Analysis method and acquiring highly detailed images up to 77 M pixels spanning large areas of complex mineral sample sections.

Maia X-ray fluorescence imaging: Capturing detail in complex natural samples

Motivated by the challenge of capturing complex hierarchical chemical detail in natural material from a wide range of applications, the Maia detector array and integrated realtime processor have been developed to acquire X-ray fluorescence images using X-ray Fluorescence Microscopy (XFM). Maia has been deployed initially at the XFM beamline at the Australian Synchrotron and more recently, demonstrating improvements in energy resolution, at the P06 beamline at Petra III in Germany. Maia captures fine detail in element images beyond 100 M pixels. It combines a large solid-angle annular energy-dispersive 384 detector array, stage encoder and flux counter inputs and dedicated FPGA-based real-time event processor with embedded spectral deconvolution. This enables high definition imaging and enhanced trace element sensitivity to capture complex trace element textures and place them in a detailed spatial context. Maia hardware and software methods provide per pixel correction for dwell, beam flux variation, dead-time and pileup, as well as off-line parallel processing for enhanced throughput. Methods have been developed for real-time display of deconvoluted SXRF element images, depth mapping of rare particles and the acquisition of 3D datasets for fluorescence tomography and XANES imaging using a spectral deconvolution method that tracks beam energy variation.

A single crystal bent Laue monochromator for coronary angiography

Abstract A new monochromator has been developed for the human coronary angiography project at the National Synchrotron Light Source. It is a single bent crystal of silicon in the Laue transmission geometry. The design, testing and use of this monochromator in a human imaging procedure will be discussed.

Reduced As components in highly oxidized environments: Evidence from full spectral XANES imaging using the Maia massively parallel detector

Abstract Synchrotron X-ray fluorescence (SXRF) and X-ray absorption spectroscopy (XAS) have become standard tools to measure element concentration, distribution at micrometer- to nanometer-scale, and speciation (e.g., nature of host phase; oxidation state) in inhomogeneous geomaterials. The new Maia X-ray detector system provides a quantum leap for the method in terms of data acquisition rate. It is now possible to rapidly collect fully quantitative maps of the distribution of major and trace elements at micrometer spatial resolution over areas as large as 1 × 5 cm2. Fast data acquisition rates also open the way to X-ray absorption near-edge structure (XANES) imaging, in which spectroscopic information is available at each pixel in the map. These capabilities are critical for studying inhomogeneous Earth materials. Using a 96-element prototype Maia detector, we imaged thin sections of an oxidized pisolitic regolith (2 × 4.5 mm2 at 2.5 × 2.5 μm2 pixel size) and a metamorphosed, sedimentary exhalative Mn-Fe ore (3.3 × 4 mm2 at 1.25 × 5 μm2). In both cases, As K-edge XANES imaging reveals localized occurrence of reduced As in parts of these oxidized samples, which would have been difficult to recognize using traditional approaches.

Development of a high-rate high-resolution detector for EXAFS experiments

A new detector for EXAFS experiments is being developed. It is based on a multi-element Si sensor and dedicated readout application specific integrated circuit (ASIC). The sensor is composed of 384 pixels, each having 1 mm/sup 2/ area, arranged in four quadrants of 12/spl times/8 elements and it is wire-bonded to 32-channel ASICs. Each channel implements low-noise preamplification with self-adaptive continuous reset, high-order shaper, bandgap referenced baseline stabilizer, one threshold comparator, and two digital-analog converter (DAC) adjustable window comparators, each followed by a 24-bit counter. Fabricated in 0.35 /spl mu/m CMOS, the ASIC dissipates about 8 mW per channel. First measurements show at room temperature a resolution of 14e/sup -/ rms without the detector and 40 e/sup -/ rms (340 eV) with the detector connected and biased. Cooling to -35 C a full width at half maximum (FWHM) of 205 eV (167 eV from electronics) was measured at the Mn-K/spl alpha/ line. A resolution of about 300eV was measured for rates approaching 100 kc/s per channel, corresponding to an overall rate in excess of 10 Mc/s/cm/sup 2/. Channel-to channel threshold dispersion after DAC adjustment 2.5 was e/sup -/ root mean square.

Sagittal focusing of high-energy synchrotron X-rays with asymmetric Laue crystals. I. Theoretical considerations

The ability of asymmetric Laue crystals to focus X-rays sagittally is demonstrated. The extent of such focusing is similar to that of sagittal focusing by a Bragg crystal, except for a factor related to the asymmetry angle. The anticlastic bending facilitates the use of inverse-Cauchois geometry in the meridional plane to provide better energy resolution and to increase the photon flux by an order of magnitude compared with traditional sagittal focusing with Bragg crystals. Furthermore, for sagittal focusing at X-ray energies above 30 keV, a Laue crystal is preferred to a Bragg crystal because the length of the beams footprint on a Laue crystal, unlike on a Bragg crystal, is small and insensitive to energy. The conditions imposed on the asymmetry angle of the Laue crystal to achieve simultaneous sagittal focusing and inverse-Cauchois geometry in the meridional plane are derived for both single-crystal and double-crystal fixed-exit sagittally focusing monochromators.

Sagittal focusing of high-energy synchrotron X-rays with asymmetric Laue crystals. II. Experimental studies

The use of bent asymmetric Laue crystals to focus synchrotron X-rays sagittally from 15 to 50 keV is described. A four-bar bender, bending a rectangular planar crystal, produced the necessary sagittal and meridional bending for this unique application. Adjustments of the tilt angle and height of the bent crystal resulted in first- and second-order corrections, respectively, to the dependence of the angle of diffraction on the horizontal position on the crystal. After these corrections, the remaining variation of the diffraction angle was of the order of 10 µrad. The theoretical sagittal focal length was verified. A prototype of a double-crystal sagittally focusing monochromator was constructed and tested, using two identical Laue crystals. A horizontal divergence of 3 mrad was focused to a horizontal dimension of about 0.4 mm. The X-ray flux density at the focus was a few hundred times larger than that of unfocused X-rays.

Computed tomography with monochromatic X-rays from the National Synchrotron Light Source

Abstract A multiple-energy computed tomography (MECT) system that employs monochromatic and tunable 33–100 keV X rays from a superconducting wiggler at the National Synchrotron Light Source is being developed at Brookhaven National Laboratory. The CT configuration is that of a fixed, horizontal fan-shape beam and a subject seated in a rotating chair. Two quantitative CT methods will be used: a) K-edge subtraction of intravenously administered iodine (or a heavier element) to image brain tumors, large blood vessels of the lower head and neck, and arteriovenous malformations; and b) dual photon absorptiometry to obtain two brain CT images that map the low−Z elements and the intermediate−Z elements (i.e. P, S, Cl, K, Ca, and Fe) separately. The system is expected to provide 0.5 mm spatial resolution, horizontally, with unprecedented image contrast and accuracy of quantification. The system will employ a two-crystal monochromator and a high-purity Ge linear array detector.