High-resolution Monochromator Research Articles

A cryogenically stabilized meV-monochromator for hard X-rays

The design and performance results for a cryogenically stabilized high-resolution monochromator for 23.880 keV (lambda = 52 pm) X-rays are presented. The four-crystal-reflection monochromator is suitable for nuclear resonant scattering measurements from 119Sn compounds using synchrotron radiation. The design includes a low-vibration cryostat that maintains two of the four crystal reflections at a temperature where the coefficient for thermal expansion of the crystalline material (silicon) vanishes. Test results demonstrate a 1.3 meV bandwidth with negligible broadening due to vibrations and a spectral efficiency of 37% when used with an undulator source.

Four-reflection “nested” meV-monochromators for 20–30 keV synchrotron radiation

We present the design and performance of three silicon high-resolution ( E / Δ E ≈ 2 – 5 × 10 7 ) monochromators for synchrotron radiation that work at energies corresponding to nuclear excited states in 151Eu (21 542 eV), 119Sn (23 880 eV), and 161Dy (25 651 eV). The design of each monochromator is quite similar with the exception of the silicon crystal reflections that are used and the surface asymmetry angles that are chosen. We give the basic design underlying all three monochromators along with a table of the specific parameters used for each one. Performance in terms of resolution and spectral efficiency are measured and compared to theoretical expectations. Measurements of lattice excitations in different solids containing the aforementioned isotopes demonstrate the utility of each monochromator. Possible improvements to performance are presented.

High-resolution neutron diffraction monochromators

High-resolution neutron diffraction monochromators

Analytical Characteristics of a Continuum-Source Tungsten Coil Atomic Absorption Spectrometer

A continuum-source tungsten coil electrothermal atomic absorption spectrometer has been assembled, evaluated, and employed in four different applications. The instrument consists of a xenon arc lamp light source, a tungsten coil atomizer, a Czerny-Turner high resolution monochromator, and a linear photodiode array detector. This instrument provides simultaneous multi-element analyses across a 4 nm spectral window with a resolution of 0.024 nm. Such a device might be useful in many different types of analyses. To demonstrate this broad appeal, four very different applications have been evaluated. First of all, the temperature of the gas phase was measured during the atomization cycle of the tungsten coil, using tin as a thermometric element. Secondly, a summation approach for two absorption lines for aluminum falling within the same spectral window (305.5-309.5 nm) was evaluated. This approach improves the sensitivity without requiring any additional preconcentration steps. The third application describes a background subtraction technique, as it is applied to the analysis of an oil emulsion sample. Finally, interference effects caused by Na on the atomization of Pb were studied. The simultaneous measurements of Pb and Na suggests that negative interference arises at least partially from competition between Pb and Na atoms for H2 in the gas phase.

Crystallographic data collection using a 0.22% bandwidth multilayer

To bridge the gap between traditional multilayer and crystal optics a high-resolution multilayer monochromator with a bandwidth of 0.22% has been designed and installed on a bending-magnet beamline (F3) at the Cornell High Energy Synchrotron Source (CHESS) to provide an unfocused monochromatic X-ray beam for protein crystallography experiments. Crystallographic data of excellent quality from a medium-sized protein, Concanavalin A, were collected and processed using standard crystallographic programs. The data were successfully used for a structure solution and refinement. The flux from the multilayer monochromator is enhanced, relative to that from a flat Si(111) monochromator, by a factor of 5; consequently, data collection is faster and/or smaller samples may be used. At the same time, the bandwidth is narrow enough to avoid streaked spots. This experiment suggests that multilayer optics may play a valuable role in satisfying the demands of the structural biology community for rapid X-ray data collection, particularly at under-utilized bending-magnet beamlines.

Profiled bar transmission gratings: soft-x-ray calibration of new Kirchoff solutions.

A new analytical model, derived rigorously from scalar diffraction theory, accurately fits soft-x-ray measurements of symmetrical profile gold transmission gratings in all diffracted orders. The calibration system selects numerous photon energies by use of a high-resolution grazing-incidence monochromator and a dc e-beam source. Fine-period free-standing gratings exhibit limited performance and require such testing to determine parameters of and select acceptable gratings for use in time-resolved (0.25 ns) spectrographs of known radiometric response. Unfolded spectra yield a Z-pinch plasma peak kT approximately 250 eV, total radiated energy approximately 900 kJ, and a pinch-driven gold-wall hohlraum Planckian kT approximately 86 eV.

Method development for the determination of thallium in coal using solid sampling graphite furnace atomic absorption spectrometry with continuum source, high-resolution monochromator and CCD array detector

The determination of thallium by graphite furnace atomic absorption spectrometry (GFAAS) is plagued by several difficult-to-control interferences. High-resolution continuum-source GFAAS, a technique not yet commercially available, was used to investigate and eliminate spectral interferences, and to develop a reliable method for the determination of thallium in coal using direct solid sampling. The resolution of 2.1 pm per pixel, and the display of the spectral environment ±0.2 nm on both sides of the analytical line were ideally suited for that purpose. The thallium signal was preceded by excessive non-specific absorption due to the coal matrix when pyrolysis temperatures ≤600 °C were used, and a characteristic molecular absorption with pronounced fine structure was following the atomic absorption. With a pyrolysis temperature of 700 °C the non-specific absorption at the beginning of the atomization stage could be eliminated, and using an atomization temperature of 1700 °C, and no modifier, the atomic absorption could be separated in wavelength and in time from the molecular structures, making possible an interference-free determination of thallium, using Pixel 260 at 276.8085 nm for background correction. The results obtained for 11 coal samples and one coal fly ash were in agreement at a 95% confidence level without a modifier, with palladium added in solution, and with ruthenium as permanent modifier, respectively, using aqueous standards for calibration. A characteristic mass of m 0=12 pg and 5.5 pg was obtained with the center pixel only, and the center pixel ±1, respectively. The precision, expressed as relative standard deviation was typically better than 5%, and the limit of detection, based on three times the standard deviation of the coal with the lowest analyte content, was 0.01 μg g −1.

Intensity interferometry for the study of x-ray coherence

Intensity interferometry has been performed for the study of x-ray coherence. A high-resolution monochromator at $E=14.41\mathrm{keV}$ was developed for enhancing the interference signal. Transverse coherence profiles of undulator radiation were evaluated from measurements of mode numbers. The obtained coherence length in vertical, which is perpendicular to the scattering plane of the monochromator, was proportional to the distance from the light source, as is expected from the Van Cittert--Zernike theorem. Vertical emittances of the storage ring were determined from the measured coherence lengths. Degradation of transverse coherence with phase object was measured and analyzed based on the propagation law of mutual intensity.

Combining flat crystals, bent crystals and compound refractive lenses for high-energy X-ray optics.

Compound refractive lenses (CRLs) are effective for collimating or focusing high-energy X-ray beams (50-100 keV) and can be used in conjunction with crystal optics in a variety of configurations, as demonstrated at the 1-ID undulator beamline of the Advanced Photon Source. As a primary example, this article describes the quadrupling of the output flux when a collimating CRL, composed of cylindrical holes in aluminium, is inserted between two successive monochromators, i.e. a modest-energy-resolution premonochromator followed by a high-resolution monochromator. The premonochromator is a cryogenically cooled divergence-preserving bent double-Laue Si(111) crystal device delivering an energy width DeltaE/E approximately 10(-3), which is sufficient for most experiments. The high-resolution monochromator is a four-reflection flat Si(111) crystal system resembling two channel-cuts in a dispersive arrangement, reducing the bandwidth to less than 10(-4), as required for some applications. Tests with 67 and 81 keV photon energies show that the high-resolution monochromator, having a narrow angular acceptance of a few microradians, exhibits a fourfold throughput enhancement due to the insertion of a CRL that reduces the premonochromatized beam's vertical divergence from 29 micro rad to a few microradians. The ability to focus high-energy X-rays with CRLs having long focal lengths (tens of meters) is also shown by creating a line focus of 70-90 micro m beam height in the beamline end-station with both the modest-energy-resolution and the high-energy-resolution monochromatic X-rays.

Ｘ線高分解能分光器を用いた放射光コヒーレンス計測

X-ray intensity interferometry with high-resolution monochromator was developed at the SPring-8 coherent X-ray beamlines. Transverse and longitudinal X-ray coherence properties, as well as electron beam parameters in the storage ring, were determined in high accuracy. Application to XFEL diagnostics is discussed.

Development of Scanning-Type Synchrotron Radiation Mössbauer Microscope Using Focused X-Ray

A scanning-type synchrotron radiation Mössbauer microscope was designed and installed at the nuclear resonance beamline BL11XU of the SPring-8 facility. The focused Mössbauer probe beam (<φ20 µm) is obtained by the combination of a high-resolution monochromator, a multilayer X-ray focusing mirror and a pinhole slit. Using this Mössbauer microscope, we have performed, for the first time, the synchrotron radiation Mössbauer microscopic measurements of nuclear resonant forward scattering from an iron borate single crystal as a function of the sample position. It was found that the observed Mössbauer time spectra depend on the direction of the local hyperfine magnetic field and the local specimen thickness.

Dissociative electron attachment to gas-phase glycine.

By using a high-resolution electron energy monochromator low-energy electron attachment to gas-phase glycine (H2NCH2COOH, or G) has been studied by means of mass spectrometric detection of the product anions. In the same way as for several other biologically relevant molecules no stable parent anion was formed by free electron attachment. The largest dissociative electron attachment (DEA) cross-section, approximately 5x10(-20) m2, was observed for (G-H)-+H at an electron energy of 1.25 eV. Glycine and formic acid (HCOOH) have several common features, because a precursor ion can be characterized by electron attachment to the unoccupied pi* orbital of the -COOH group. At higher incident electron energies several smaller fragment anions are formed. Except for H-, which could not be observed in this study, there was good agreement with an earlier investigation by Gohlke et al.

Studies on Nuclear Resonant Scattering of Synchrotron Radiation by 40 K

The studies on nuclear resonant scattering by 40K using synchrotron radiation are reviewed. Brilliant and high pure synchrotron radiation permitted us to observe the nuclear resonant forward scattering by 40K in a powdered KCl sample, the excitation of which is impossible with ordinary radioactive sources. Furthermore, nuclear resonant inelastic scattering of synchrotron radiation by 40K in the KCl sample at room temperature has been measured using a high-resolution monochromator. Adding to these, from the excitation experiments of 40K, the energy and lifetime of the first excited state of 40K were confirmed. These measurements clearly show that the studies on the electronic states through hyperfine interactions and the dynamical properties of potassium atoms, which are very important in material science and biology, are possible. It should be noted that 40K is the natural isotope of potassium and weakly radioactive. Our observation of forward and inelastic scattering of the radioactive nuclide 40K will lead to further studies on other radioactive nuclides the resonant forward and inelastic scattering of which are not observed to date.

High-resolution monochromator for nuclear resonant scattering by151Eu and149Sm

High-resolution monochromator for nuclear resonant scattering by¹⁵¹Eu and¹⁴⁹Sm

Ultrahigh-resolution x-ray monochromators for elastic and inelastic x-ray scattering studies (abstract) (invited)

High-resolution spectroscopies that use hard x rays like nuclear resonant scattering and inelastic x-ray scattering require monochromatization to the meV level. Currently, tunable x-ray monochromators using silicon allow one to achieve sub-meV energy bandwidths in the 10–30 keV energy range. Attempts to improve the energy resolution beyond 108 encounter issues such as stability, efficiency, and crystal-quality-limited resolution. Cryogenically cooling the silicon can potentially mitigate the problems related to thermal stability, as well as improve the efficiency. Cooling high-resolution monochromators, while maintaining the requisite 10 nrad angular control over the crystals, poses a challenging technical problem. Recent attempts to improve the limits of energy resolution and to improve efficiency and stability of high-resolution monochromators with cryogenic cooling will be discussed.

A SOFT X-RAY UNDULATOR BEAMLINE AT THE ADVANCED LIGHT SOURCE WITH CIRCULAR AND VARIABLE LINEAR POLARIZATION FOR THE SPECTROSCOPY AND MICROSCOPY OF MAGNETIC MATERIALS

A new undulator beamline at the Advanced Light Source, Lawrence Berkeley National Laboratory is described. This new beamline has an Apple II type undulator which produces linearly and elliptically polarized X-rays. A high resolution monochromator directs the radiation to two branchlines. The first branchline is optimized for spectroscopy and accommodates multiple endstations simultaneously. The second branchline features a photoemission electron microscope. A novel feature of the beamline is the ability to produce linearly polarized radiation at arbitrary, user-selectable angles. Applications of the new beamline are also described.

Nuclear Resonant Inelastic and Forward Scattering of Synchrotron Radiation by 40K

We achieved excitation of the first excited state of 40K and confirmed both energy and lifetime. Furthermore, we observed nuclear resonant inelastic scattering by 40K in a powdered KCl sample at room temperature using a high-resolution monochromator. The time spectrum of the nuclear resonant forward scattering was measured at 50 K. Our observations of nuclear resonant inelastic and forward scattering by 40K make electronic and dynamic studies for potassium practical. The measurements of nuclear resonant scattering for the radioactive 40K nuclide will enable and lead to further studies of other radioactive nuclides.

Energy-selective (+, +) monolithic monochromator and relative lattice-spacing measurement of Si wafers with synchrotron radiation

X-ray optic systems have been developed at beamline BL-3C2 of the Photon Factory, KEK, for the study of the relative lattice spacings of Si wafers using synchrotron radiation. Since synchrotron radiation has no characteristic (wavelength) spectral lines, unlike an X-ray tube, a new tool has been introduced into the system as a wavelength-selective device – a (+, +) high-resolution channel-cut monolithic monochromator. Using two types of monolithic monochromator, two schemes are proposed and applied to the study of the lattice spacings of Si wafers. The lattice-spacing differences are determined in the sub-p.p.m range; for example, in scheme 1 and scheme 2 we obtain 0.6 p.p.m. and 0.2 p.p.m., respectively. One of the practical advantages of this system is that it can be applied for a fast and precise measurement of the lattice-spacing changes due to the doping and defects in Si, GaAs and other single crystals.

A monolithic monochromator–collimator for high-resolution X-ray diffraction

The possibility of finding, for a given X-ray wavelength, the conditions for obtaining multiple coplanar reflections in a single block of crystal is investigated. It is found that by introducing a small relative tilt between two parts of the crystal, the conditions for a high-resolution X-ray monochromator for conventional and synchrotron X-ray sources can be obtained. The design of a new high-resolution monochromator–collimator based on a single crystal, which takes advantage of the existence for almost any wavelength ofnandmplanes in the single crystal that lie near the Bragg condition, is presented. A weak link between the two reflecting surfaces is used to align the crystal planes and to obtain efficient reflections in the dispersive configuration. DuMond diagrams are used to evaluate the total diffracted intensity and the resolution of such a monochromator. The experimental results obtained from prototypes made of single crystals of silicon and germanium are in good agreement with theoretical predictions. This new type of monochromator offers the advantages of a compact design and simple alignment.

A compact optical design for Bragg reflections near backscattering

A very compact in-line X-ray optical design is presented which is optimized for use with Bragg reflections close to backscattering (Bragg angles near 90°). The essential idea is to use a low-order Bragg reflection to couple the X-ray beam into a small channel-cut backscattering crystal. The design is demonstrated in an almost theoretically performing high-resolution monochromator providing 2 × 108 photons s−1 in a 0.52 meV bandwidth at 25.65 keV. The monochromator is used to measure inelastic nuclear scattering from phonons in 161Dy-containing samples.