C. Cusatis

A two-crystal monochromator for the UVX ring of LNLS

A two‐crystal x‐ray monochromator was built at LNLS. It is based on the Golovchenko [J. A. Golovchenko, R. A. Levesque, and P. L. Cowan, Rev. Sci. Instrum. 52, 51 (1981)] geometry with one rotation and two translations in order to tune the wavelength and keep constant the position of the monochromatic beam, respectively. The Bragg angle can vary from 10° to 80° using a standard high precision external goniometer whose minimum step is 0.001°. The two translations are based on a leaf spring device, with a maximum wobbling of ±2 arcsec along 50 mm. Fine tuning between the two crystals and detuning for harmonic rejection are produced by elastic devices using the magnetic force between a permanent magnet and a solenoid acting on a weak link of the second crystal. The monochromator housing is vacuum compatible. The equipment was tested using a conventional x‐ray source and a standard control system. It will be used associated with classical extended x‐ray absorption fine structure (EXAFS) and the high precision...

An inelastic X-ray scattering spectrometer at LNLS

A high-resolution spectrometer aimed at performing experiments of inelastic X-ray scattering by electronic excitations is described. The spectrometer has been installed at the D12A-XRD1 beamline of the National Synchrotron Light Laboratory (LNLS), in Campinas, Brazil. Synchrotron radiation is monochromated to about 6 keV and focused horizontally onto the sample by a sagittally focusing Si(111) double-crystal monochromator in non-dispersive setting. The spectrometer operates in Rowland circle geometry and is based on a focusing Si(333) analyser in near-backdiffraction geometry for energy analysis of inelastically scattered photons. The analyser works at a fixed Bragg angle, so energy transfers are obtained by varying the incident photon energy. A relative energy resolution of the whole spectrometer of approximately 1.5 x 10(-4) at 5.93 keV has been achieved. As an example of application, inelastic X-ray scattering by plasmon excitation in polycrystalline Be was measured. Test results demonstrate that inelastic X-ray scattering experiments with eV energy resolution and an acceptable counting rate are feasible at the LNLS when focused on plasmon and particle-hole excitations.

First experiments on diffraction-enhanced imaging at LNLS.

Diffraction-enhanced images have been obtained using two silicon crystals in a non-dispersive set-up at the XRD2 beamline at the Brazilian Synchrotron Light Laboratory (LNLS). A first asymmetrically cut silicon crystal using the (333) reflection vertically expanded the monochromated beam from 1 mm to 20 mm allowing the imaging of the whole sample without movements. A symmetrically cut Si(333) second crystal was used as a Bragg analyzer. Images of biological samples including human tissue were recorded using a direct-conversion CCD detector resulting in enhancement of the contrast compared with absorption-contrast images.

X-ray Back-Diffraction Profiles with an Si (111) Plate

A two- and, alternatively, a four-crystal monochromator were used for simultaneous measurements of the profiles backward (h) and forward (o) diffracted by a thin Si (111) crystal plate for diffraction angles up to exactly 90 ° at DCI-LURE (Orsay). It is shown that the set-up with a four-crystal monochromator allows the characterization of the back-diffraction region for any crystal plate reflection. Asymmetry and full width at half-maximum (FWHM) of the experimental backwarddiffraction profiles are analyzed. Possible simultaneous diffractions occurring near 90 ° incidence, giving extra peaks in the forward-diffracted profiles, are studied. The good contrast of the o-beam profiles suggests that the back-diffracted o beam could be used as a highly monochromatic beam.

Installation and operation of the LNLS double-crystal monochromator at CAMD

A new x‐ray beamline has been installed at CAMD utilizing a two‐crystal monochromator designed and built at LNLS. The beamline will operate in the 2–18 keV range using up to 4 mrad of dipole radiation from the CAMD storage ring. The monochromator maintains a fixed exit beam and fixed positions of the beam on the two crystals using mutually perpendicular elastic translations. With the ring operating at 1.5 GeV and 160 mA, Si(220) crystals will provide a flux of ∼3(109) photons/s/mrad at 8 keV, with an energy resolution ΔE<2 eV, to the experimental hutch. The beamline is equipped with an EXAFS endstation and will also be used for other x‐ray applications at CAMD. First results are presented.

Diamond thermal expansion measurement using transmitted X-ray back-diffraction.

The linear thermal expansion coefficient of diamond has been measured using forward-diffracted profiles in X-ray backscattering. This experimental technique is presented as an alternative way of measuring thermal expansion coefficients of solids in the high-resolution Bragg backscattering geometry without the intrinsic difficulty of detecting the reflected beam. The temperature dependence of the lattice parameter is obtained from the high sensitivity of the transmitted profiles to the Bragg angle variation with temperature. The large angular width of the backscattering profiles allows the application of this technique to mosaic crystals with high resolution. As an application of this technique the thermal expansion coefficient of a synthetic type-Ib diamond (110) single crystal was measured from 10 to 300 K. Extremely low values (of the order of 1 x 10(-7) +/- 5 x 10(-7)) for the linear thermal expansion coefficient in the temperature range from 30 to 90 K are in good agreement with other reported measurements.

Source effects in analyzer-based X-ray phase contrast imaging with conventional sources

Several recent papers have shown the implementation of analyzer based X-ray phase contrast imaging (ABI) with conventional X-ray sources. The high flux is always a requirement to make the technique useful for bio-medical applications. Here, we present and discuss three important parameters, which need to be taken into account, when searching for the high flux ABI: anisotropic magnification, double image, and source size spread due to intrinsic dispersive diffraction by asymmetrically cut crystals. These parameters, if not well optimized, may cause important features in the acquired images which can mislead the interpretation. A few ways to minimize these effects are implemented and discussed, including some experimental results.

Analyzer-based x-ray phase-contrast microscopy combining channel-cut and asymmetrically cut crystals.

An analyzer-based x-ray phase-contrast microscopy (ABM) setup combining a standard analyzer-based x-ray phase-contrast imaging (ABI) setup [nondispersive 4-crystal setup (Bonse-Hart setup)] and diffraction by asymmetrically cut crystals is presented here. An attenuation-contrast microscopy setup with conventional x-ray source and asymmetrically cut crystals is first analyzed. Edge-enhanced effects attributed to phase jumps or refraction/total external reflection on the fiber borders were detected. However, the long exposure times and the possibility to achieve high contrast microscopies by using extremely low attenuation-contrast samples motivated us to assemble the ABM setup using a synchrotron source. This setup was found to be useful for low contrast attenuation samples due to the low exposure time, high contrast, and spatial resolution found. Moreover, thanks to the combination with the nondispersive ABI setup, the diffraction-enhanced x-ray imaging algorithm could be applied.

High-quality quartz single crystals for high-energy-resolution inelastic X-ray scattering analyzers

High-quality quartz (α-SiO2) crystals are characterized, and their use for inelastic X-ray scattering analyzers is presented and discussed.

Long and compact x-ray pathway for experiments requiring high coherent x-ray beams.

A long x-ray pathway based on an x-ray back-diffraction cavity for coherent x-ray beam experiments is presented. In the present work, such a setup was tested and used for propagation-based x-ray phase contrast imaging (PBI). This setup showed to be useful for PBI purposes, with the advantage of being compact (3 m long) when compared with long x-ray synchrotron beamlines with dimensions from tens to hundreds of meters.