Double Crystal Monochromator Research Articles

Analysis and interpretation of the first monochromatic X-ray tomography data collected at the Australian Synchrotron Imaging and Medical beamline

The first monochromatic X-ray tomography experiments conducted at the Imaging and Medical beamline of the Australian Synchrotron are reported. The sample was a phantom comprising nylon line, Al wire and finer Cu wire twisted together. Data sets were collected at four different X-ray energies. In order to quantitatively account for the experimental values obtained for the Hounsfield (or CT) number, it was necessary to consider various issues including the point-spread function for the X-ray imaging system and harmonic contamination of the X-ray beam. The analysis and interpretation of the data includes detailed considerations of the resolution and efficiency of the CCD detector, calculations of the X-ray spectrum prior to monochromatization, allowance for the response of the double-crystal Si monochromator used (via X-ray dynamical theory), as well as a thorough assessment of the role of X-ray phase-contrast effects. Computer simulations relating to the tomography experiments also provide valuable insights into these important issues. It was found that a significant discrepancy between theory and experiment for the Cu wire could be largely resolved in terms of the effect of the point-spread function. The findings of this study are important in respect of any attempts to extract quantitative information from X-ray tomography data, across a wide range of disciplines, including materials and life sciences.

X-ray absorption fine structure (XAFS) spectroscopy using synchrotron radiation

The X-ray absorption fine structure (XAFS) spectra are best recorded when a highly intense beam of X-rays from a synchrotron is used along with a good resolution double crystal or curved crystal spectrometer and detectors like ionization chambers, scintillation counters, solid state detectors etc. Several synchrotrons around the world have X-ray beamlines dedicated specifically to XAFS spectroscopy. Fortunately, the Indian synchrotron (Indus-2) at Raja Ramanna Centre for Advanced Technology (RRCAT) at Indore has started operation. A dispersive type EXAFS beamline called BL-8 has been commissioned at this synchrotron and another beamline having double crystal monochromator (DCM) is going to be commissioned shortly. In Indian context, in order that more research workers use these beamlines, the study of XAFS spectroscopy using synchrotron radiation becomes important. In the present work some of the works done by our group on XAFS spectroscopy using synchrotron radiation have been described.

Optic Nerve Imaging Using Synchrotron Radiation (P07.254)

Objective: We performed experimental synchrotron radiation (SR) imaging techniques on the leporine optic nerve to see if high resolution, detailed images of optic nerve microstructure could reliably be obtained. Our long term objective is to pursue safe in vivo imaging for the development of animal models for the study of optic neuropathies. Background There are no previous SR imaging studies of the optic nerve in either humans or animals. SR imaging techniques including diffraction enhanced imaging (DEI), and CT planar imaging have been successfully used to image biological tissues including the porcine eye, murine internal organs, canine articular cartilage, and human breast cancer tissue. Design/Methods: Specimen preparation included previously frozen dissected rabbit globes, optic nerves and chiasm, and one whole rabbit head. These samples were preserved and imaged in 10% formalin. A double crystal monochromator was used to select a very small energy band from the polychromatic synchrotron beam. The monochromatic beam passed through samples, with an analyzer crystal similar to that in the monochromator placed after the sample. Results: The analyzer crystal was sensitive to the refractive effects within the samples. In addition, absorption and scattering effects were used to create images with differing contrast properties. By moving the analyzer crystal various images of the optic nerve and ocular structures that showed apparent absorption and refraction properties were obtained. Conclusions: By using an intense monochromatic radiation beam from a synchrotron, we were able to image microscopic structures of the leporine optic nerve and surrounding tissues using both diffraction enhanced and CT planar imaging techniques. As far as we know, we are the only synchrotron research group in the world attempting to image the optic nerve, and the work is highly experimental and preliminary. We will continue to refine our methods and techniques of image acquisition. Supported by: Saskatchewan Health Research Foundation. Disclosure: Dr. Atkins has nothing to disclose. Dr. de Jager has nothing to disclose. Dr. Wiebe has nothing to disclose. Dr. Grahn has nothing to disclose. Dr. Chapman has nothing to disclose.

Measured and calculated K-fluorescence effects on the MTF of an amorphous-selenium based CCD x-ray detector

Theoretical reasoning suggests that direct conversion digital x-ray detectors based upon photoconductive amorphous-selenium (a-Se) could attain very high values of the MTF (modulation transfer function) at spatial frequencies well beyond 20 cycles mm(-1). One of the fundamental factors affecting resolution loss, particularly at x-ray energies just above the K-edge of selenium (12.66 keV), is the K-fluorescence reabsorption mechanism, wherein energy can be deposited in the detector at locations laterally displaced from the initial x-ray interaction site. This paper compares measured MTF changes above and below the Se K-edge of a CCD based a-Se x-ray detector with theoretical expectations. A prototype 25 μm sampling pitch (Nyquist frequency = 20 cycles mm(-1), 200 μm thick a-Se layer based x-ray detector, utilizing a specialized CCD readout device (200 × 400 area array), was used to make edge images with monochromatic x-rays above and below the K-edge of Se. A vacuum double crystal monochromator, exposed to polychromatic x-rays from a synchrotron, formed the monochromatic x-ray source. The monochromaticity of the x-rays was 99% or better. The presampling MTF was determined using the slanted edge method. The theory modeling the MTF performance of the detector includes the basic x-ray interaction physics in the a-Se layer as well as effects related to the operation of the CCD and charge trapping at a blocking layer present at the CCD/a-Se interface. The MTF performance of the prototype a-Se CCD was reduced from the theoretical value prescribed by the basic Se x-ray interaction physics, principally by the presence of a blocking layer. Nevertheless, the K-fluorescence reduction in the MTF was observed, approximately as predicted by theory. For the CCD prototype detector, at five cycles mm(-1), there was a 14% reduction of the MTF, from a value of 0.7 below the K-edge of Se, to 0.6 just above the K-edge. The MTF of an a-Se x-ray detector has been measured using monochromatic x-rays above and below the K-edge of selenium. The MTF is poorer above the K-edge by an amount consistent with theoretical expectations.

<i>In Situ</i> Gas Supply System on the Powder Diffraction Beamline I11 at Diamond Light Source

Beamline I11 at Diamond began accepting users for high resolution powder diffraction experiments in Oct 2008. We present the design, key specifications, performance and the hardware of this new beamline which receives an intense and highly collimated x-ray beam generated by an in-vacuum undulator. With the simple optics (a double-crystal monochromator, harmonic rejection mirrors and slits), a high purity beam of low energy-bandpass X-rays optimised at 15 keV is delivered at the sample. The heavy duty diffraction instrument is designed to have the flexibility to house a variety of sample environments and holds two detection systems to collect high quality diffraction data, i.e. multi-analysing crystals (MAC) for high angular resolution experiments and a fast position sensitive detector (PSD) for time-resolved studies. A recent addition to the beamline capabilities is the installation of a specifically designed gas control system. This allows the in-situ dosing of a powder sample with gases such as hydrogen and carbon dioxide, at low (~10 mbar) and high pressures (<100 bar). In addition a low pressure capillary sample cell is described which is now available to users of the beamline.

Self-filtering extremely inclined X-ray crystal monochromator

It is shown that an extremely inclined X-ray double-crystal monochromator can diffract a beam with the required wavelength and at the same time may reflect a great deal of unwanted radiation in a broad range of Bragg angles. This is a generalization of the idea of Cowan & Brennan [Rev. Sci. Instrum.(1989),60, 1987–1990], which partially solves the radiation heat load problem. The properties of such a device are discussed. It is shown that in some cases the diffracted beam may be significantly broadened as a result of refraction effects. In these cases a four-crystal arrangement or an additional mirror is necessary.

Azimuthal reflection high-energy electron diffraction study of MnAs growth on GaAs(001) by molecular beam epitaxy

Azimuthal reflection high-energy electron diffraction (ARHEED) and in situ grazing incidence synchrotron x-ray diffraction techniques are employed to investigate the growth, epitaxial orientation, and interfacial structure of MnAs layers grown on GaAs(001) by molecular beam epitaxy (MBE). We demonstrate the power and reliability of ARHEED scans as a routine tool in characterizing the formation of epitaxial films. The ARHEED scans clearly reveal the formation of the rectangular MnAs unit cell during growth on GaAs(001) for a MnAs layer thickness of 2.1 ± 0.2 monolayers with a tensile strain along the MnAs[112−0] direction. A periodic coincidence site lattice, which is known to form along the MnAs [0001] direction to release the strain due to the huge lattice mismatch (∼30%) also produces periodic satellites of the diffraction spots in the ARHEED scan. The formation of different epitaxial orientations of MnAs during MBE growth can be directly observed using ARHEED scans. ARHEED is demonstrated to have a resolution similar to synchrotron x-ray diffraction with a double crystal monochromator, yielding full width at half maximum values of reflections as small as 0.005 reciprocal lattice units.

Neutron Bragg-edge-imaging for strain mapping under in situ tensile loading

Wavelength selective neutron radiography at a cold neutron reactor source was used to measure strain and determine (residual) stresses in a steel sample under plane stress conditions. We present a new technique that uses an energy-resolved neutron imaging system based on a double crystal monochromator and is equipped with a specially developed (in situ) biaxial load frame to perform Bragg edge based transmission imaging. The neutron imaging technique provides a viewing area of 7 cm by 7 cm with a spatial resolution on the order of ∼ 100 μm. The stress-induced shifts of the Bragg edge corresponding to the (110) lattice plane were resolved spatially for a ferritic steel alloy A36 (ASTM international) sample. Furthermore it is demonstrated that results agree with comparative data obtained using neutron diffraction and resistance based strain-gauge rosettes.

X-ray collimation by crystals with precise parabolic holes based on diffractive–refractive optics

Two crystals with precise parabolic holes were used to demonstrate sagittal beam collimation by means of a diffractive-refractive double-crystal monochromator. A new approach is introduced and beam collimation is demonstrated. Two Si(333) crystals with an asymmetry angle of α = 15° were prepared and arranged in a dispersive position (+,-,-,+). Based on theoretical calculations, this double-crystal set-up should provide tunable beam collimation within an energy range of 6.3-18.8 keV (Θ(B) = 71-18.4°). An experiment study was performed on BM05 at ESRF. Using 8.97 keV energy, the beam profile at various distances was measured. The experimental results are in good agreement with theoretical predictions. Owing to insufficient harmonic suppression, the collimated (333) beam was overlapped by horizontally diverging (444) and (555) beams.

Phase retrieval using polychromatic illumination for transmission X-ray microscopy

An alternative method for quantitative phase retrieval in a transmission X-ray microscope system at sub-50-nm resolution is presented. As an alternative to moving the sample in the beam direction in order to analyze the propagation-introduced phase effect, we have illuminated the TXM using X-rays of different energy without any motor movement in the TXM system. Both theoretical analysis and experimental studies have confirmed the feasibility and the advantage of our method, because energy tuning can be performed with very high energy resolution using a double crystal monochromator at a synchrotron beam line, and there is zero motor error in TXM system in our approach. High-spatial-resolution phase retrieval is accomplished using the proposed method.

Phase retrieval using polychromatic illumination for transmission X-ray microscopy

An alternative method for quantitative phase retrieval in a transmission X-ray microscope system at sub-50-nm resolution is presented. As an alternative to moving the sample in the beam direction in order to analyze the propagation-introduced phase effect, we have illuminated the TXM using X-rays of different energy without any motor movement in the TXM system. Both theoretical analysis and experimental studies have confirmed the feasibility and the advantage of our method, because energy tuning can be performed with very high energy resolution using a double crystal monochromator at a synchrotron beam line, and there is zero motor error in TXM system in our approach. High-spatial-resolution phase retrieval is accomplished using the proposed method.

Synchrotron X-Ray Absorption Study of Cu and Mn Doped BiFeO3-BaTiO3 Multiferroic Ceramics

In this work, an experimental X-ray Absorption Spectroscopy (XAS) measurement was employed to determine the local structure and valency of Cu and Mn in BiFeO3-BaTiO3. Synchrotron x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) experiments were performed on Cu-doped and Mn-doped BiFeO3-BaTiO3 samples. The Cu- and Mn-doped BiFeO3-BaTiO3 ceramic samples were used for the XAS experiment. XAS spectra at the Cu and Mn K-edge were recorded in flurorescent mode with 13-element Ge detector. The spectra were collected at ambient temperature with a Ge(111) double crystal monochromator and recorded after performing an energy calibration. The features of the measured Cu and Mn K-edge XANES was consistent with Cu and Mn on the Fe/Ti site and inconsistent with Cu and Mn on other sites. The clear agreement was the strongest evidence of Cu and Mn substituting for B-site in BiFeO3-BaTiO3 materials. In addition, the valency of both Cu and Mn ions in BiFeO3-BaTiO3 materials was also confirmed.

Kyushu University Beamline, BL06, at SAGA Light Source

Kyushu University has installed the hard X-ray beamline, BL06, at bending magnet source of SAGA Light Source in Japan. It is designed for X-ray absorption fine structure (XAFS) spectroscopy and small-angle X-ray scattering (SAXS) experiments. The X-ray energy covered by the beamline ranges from 2.1 to 23 keV using a Si(111) flat double-crystal monochromator. Two bent cylindrical-type focusing mirrors are used, each with a different focal point. They are set in the optics section and can be used independently. One of the mirrors has a focal distance of 6 m, which corresponds to the sample stage for XAFS experiments, while the second mirror focuses at 10 m, corresponding to the detector for the SAXS experiments. The photon flux measured by the ion chamber at mirror focal point is 1010 phs/s. The experimental hutch houses the detection equipment for both XAFS and SAXS. For XAFS studies, a set of ion chambers for transmission mode and a Lytle detector and a Si drift detector for fluorescence yield mode are available. For SAXS studies, the camera pass length can be chosen from 0.5 to 2.5 m with 0.5 m increments in between, and an image plate is operated as signal detector. The beamline will be opened for user operation around summer 2010.

Optics concept for a pair of undulator beamlines for MX

We describe a concept for x-ray optics to feed a pair of macromolecular crystallography (MX) beamlines which view canted undulator radiation sources in the same storage ring straight section. It can be deployed at NSLS-II and at other low-emittance third-generation synchrotron radiation sources where canted undulators are permitted, and makes the most of these sources and beamline floor space, even when the horizontal angle between the two canted undulator emissions is as little as 1-2 mrad. The concept adopts the beam-separation principles employed at the 23-ID (GM/CA-CAT) beamlines at the Advanced Photon Source (APS), wherein tandem horizontally-deflecting mirrors separate one undulator beam from the other, following monochromatization by a double-crystal monochromator. The scheme described here would, in contrast, deliver the two tunable monochromatic undulator beams to separate endstations that address rather different and somewhat complementary purposes, with further beam conditioning imposed as required. A downstream microfocusing beamline would employ dual-stage focusing for work at the micron scale and, unique to this design, switch to single stage focusing for larger beams. On the other hand, the upstream, more highly automated beamline would only employ single stage focusing.

Design and performance of the 33-BM beamline at the Advanced Photon Source

The APS sector 33 bending magnet beamline was designed to provide high X-ray flux with relatively small focal spot (1 mm×0.5 mm with ∼10 12 ph/s/100 mA flux) and energy resolution limited mostly by the intrinsic resolution of the monochromator optics, δE / E =1.5×10 −4 . The beamline accepts 4 mrad of the dipole radiation fan and uses a fixed offset design. A collimating mirror is followed by a double-crystal monochromator with a sagitally bent Si second crystal. A second mirror is dynamically bent to vertically focus or to collimate the beam at the experiment location. This design successfully delivers focused X-rays with an energy range from 5 to 38 keV for use in diffraction measurements of thin films, interface structures and bulk materials. The monochromator has scanning capabilities that also enable anomalous scattering techniques. Experiments that demonstrate the performance of the beamline will be described.

PID feedback control of monochromator thermal stabilization

The desire for increasingly smaller X-ray beams for macromolecular crystallography experiments also stimulates the need for improvements in beam stability. There are numerous sources of instability, which influence beam quality on the micron-size scale. Typically, the most problematic source is thermal drift within the double crystal monochromators . In addition to using liquid nitrogen to indirectly cool both the first and second crystals, GM/CA-CAT previously used a combination of flowing water at constant temperature and copper braiding to stabilize the mechanics, mounts, and the Compton scatter shielding. However, the copper braids inefficiently stabilized the temperature of components that were distant from the water lines. Additionally, vibrations in the water lines propagated throughout the vibrationally dampened monochromator, thereby introducing both positional and intensity instabilities in the transmitted X-ray beam. To address these problems, heating pads were placed directly onto the temperature-sensitive components, with output controlled by a PID-feedback loop. As a result, there is negligible temperature change in the first crystal radiation shielding over the entire range of operational heat loads. Additionally, the angular drift in the second crystal induced by temperature changes in other components is dramatically decreased.

Large monochromator systems at PETRA III

Abstract For the beamlines of the new synchrotron radiation source PETRA III, fixed exit double crystal monochromators with specific features were developed. To achieve a compact arrangement of the canted undulator beamlines at Sectors 2 and 6, it is necessary to shift one of the two beamlines in vertical direction. This is done by Large Offset Monochromators (LOM). One of these monochromators (LOM500, installed at beamline P03) is cooled with liquid nitrogen as it accepts the white beam. LOM1250 (installed at beamline P08) accepts a monochromatic beam and therefore needs no cooling system. The challenge with this monochromator is its large beam offset by 1.25 m. The energy range in combination with this large vertical beam offset demands for a relative crystal movement of roughly 3 m along the beam direction. This is solved by translating each crystal by up to 1.5 m. LOM1250 is equipped with a laser-based stabilisation, which allows compensating the thermal drift of the mechanical components involved in the positioning of the crystals. This is done by piezo actors below the crystals using the laser beam position after passing each crystal as feedback. With this approach we provide a closed loop system without attenuation of the X-ray beam by position monitors. The third monochromator at beamline P06 shifts the beam only by 21 mm upwards but has a linear travel of one crystal by 3.9 m. This is due to its large energy range of 4.4–90 keV using multilayer crystals. The technical design and mechanical engineering issues of the three Large Monochromator Systems at beamlines P03, P06 and P08 are highlighted in this article.

The sub-micron resolution X-ray spectroscopy beamline at NSLS-II

Abstract For many research areas such as life, environmental, earth or material sciences, novel analytical resources have to be developed for an advance understanding of complex natural and engineered systems that are heterogeneous on the micron to the tenths of microns scale. NSLS-II at BNL will be a synchrotron radiation source with an ultra-high brilliance delivering a high current (500 mA). One of the 1st six NSLS-II beamlines will be the Sub-micron Resolution X-ray spectroscopy beamline (SRX), dedicated as an analytical tool to study complex systems on a sub-micron length scale. SRX will comprise two branches thanks to a canted setup with two undulators: the first branch using Kirkpatrick–Baez mirrors as focusing optics will cover the energy range of 4.65–23 keV, allowing for XANES experiments from the Ti to the Rh K-edge. Thanks to a horizontally deflecting double crystal monochromator with maximum stability, a set of slits located on the secondary source, and two sets of complementary and quickly interchangeable KB mirrors, spectroscopy with very high spectral and spatial resolution will be achieved. The spot size will almost fully cover a range from 60×60 to 1300×500 nm2, providing an attractive adaptability of the observation scale. A 1.5 m long IVU21 will serve as a light source. The expected high flux in a sub-micron-spot (5×1012 and 7×1013 ph s−1 at maximum and lowest resolutions) will open new possibilities for spectromicroscopy of trace elements. The 2nd canted undulator will serve as an independent light source for the second branch designed for experiments with X-ray energies in the range of 2–15 keV. Using Fresnel zone plates, the spatial resolution aimed for is around 30 nm with up to 7×109 ph s−1 in the spot. This branch would be attractive for many biological applications from life and environmental science due to low-Z elements of interest within that energy range. In both experimental stations, X-ray fluorescence will be used for imaging, spectroscopy, tomography and μ-diffraction experiments.

Large offset monochromators at PETRA III

For the beamlines of the new synchrotron radiation source PETRA III, fixed-exit double crystal monochromators with specific features were developed. To achieve a compact arrangement of the canted undulator beamlines at Sectors 2, 4 and 6, it is necessary to shift one of the two beamlines in vertical direction. This is done by so-called large offset monochromators. Two of these monochromators (LOM500 and Mono-P06) accept the white beam and are therefore cooled with liquid nitrogen. The third one accepts a monochromatic beam and has no cooling system. The challenge with this device (LOM1250) is the large offset of the beam by 1.25 m. The energy range in combination with the large vertical beam offset demands for a relative crystal movement of roughly 3 m along the beam direction. This is implemented by translating each crystal by up to 1.5 m. It is equipped with a visible laser-based stabilization which allows compensating thermal drift of the mechanical components involved in the positioning of the crystals. With this novel approach the X-ray beam is not attenuated by beam position monitors.

A double crystal monochromator with self-compensation mechanism for ELETTRA XRD2 beamline

A prototype of a new double crystal monochromator (DCM) has been designed and developed for the second crystallography beamline (XRD2) at ELETTRA. The new device has to cover the 8–35 keV X-ray range. Since the corresponding diffraction angles are quite small, the choice has been to design a DCM with a fixed distance between the two crystals. As a consequence, the output beam has a small vertical displacement during the scan. This movement is compensated by means of an upstream mask, vertically moving and cutting the input beam at different heights. The movement of the mask is driven by a mechanism linked to the primary rotation of crystals (self-compensation), without any additional motor and following the displacement law required for compensation. The principle, the mechanism and the general mechanical concept of the device will be described in this paper.