Measurement of rocking curve wings at high x-ray energies

Measurements done recently at the NSLS have indicated that the level of intensity found in the wings of diffraction peaks from silicon at higher x-ray energies (>20keV) far exceeds the value which would be predicted based on the dynamical theory. We have measured Si(220) double crystal rocking curves at the 40keV fundamental and harmonics with various crystal scattering geometries: Bragg-Bragg, Laue-Bragg, Laue-Lauel. The comparison of the Bragg and Laue case diffraction geometries was done to determine scattering volume effects. Comparisons with dynamical theory calculations will be discussed. These measurements have been carried out in order to assess the level of harmonic contamination which will be present from a double crystal monochromator being designed for the X17 Superconducting Wiggler Beamline

CT imaging of small animals using monochromatized synchrotron x rays

Rats and chicken embryos were imaged in vivo with a prototype Multiple Energy Computed Tomography (MECT) system using monochromatized x rays from the X17 superconducting wiggler at the National Synchrotron Light Source. The CT configuration coated of a horizontal low-divergence, fan-shaped beam, 70 mm wide and 0.5 mm high, and a subject rotating about a vertical aids. A linear-array high-purity Ge detector with 140 elements, each 0.5 mm wide and 6 mm thick, was used with a data acquisition system that provides a linear response over almost six orders of magnitude of detector current. The dual photon absorptiometry (DPA) algorithm was applied to images of the rat head acquired at 20 and 45 keV to obtain two new images, one representing the low-Z, and the other the intermediate-Z clement group. The results indicate that the contrast resolution and the quantification accuracy of the images improve stepwise; first, with the monochromatic beam and, second, the DPA method. The system is a prototype for a brain scanner

High resolution X-ray measurements of the nematic-smectic C phase transition in the polymeric liquid crystal C-6 polysiloxane

We report on high-resolution X-ray measurements of the nematic to smectic C phase transition in the polymeric liquid crystal, C-6 polysiloxane. Preliminary results show that smectic fluctuations measured in the nematic phase are roughly consistent with a Chen and Lubensky type of theory, as was developed for monomeric liquid crystals. The phase transition in C-6 polysiloxane shows pre-transitional smectic fluctuations at least 30°C above the phase transition temperature, TNC, where TNC = 37.84 ± 0.05°C. At TNC, there is a weak first order phase transition to the smectic C phase

High-Resolution X-Ray Measurements of the A Transition in the Polymeric Liquid Crystal P4.1 Polysiloxane

We report on the first high-resolution x-ray measurements of a second-order nematic to (bilayer) smectic-A phase transition in a polymeric liquid crystal, P4.1 polysiloxane. The critical exponents of the parallel and perpendicular correlation lengths and susceptibility were ν∥=0.77±0.05, ν⊥=0.57±0.08, and γ=1.33±0.10, respectively. The bare correlation lengths, ξ0∥q0 and ξ0⊥q0, were 3.27 ± 0.08 and 1.09 ± 0.14, respectively, and are unusually large in comparison to monomeric liquid crystals

Measurement of Rocking Curve Wings at High X-Ray Energies

Measurements done recently at the NSLS have indicated that the level of intensity found in the wings of diffraction peaks from silicon at higher x-ray energies (>20keV) far exceeds the value which would be predicted based on the dynamical theory. We have measured Si(220) double crystal rocking curves at the 40keV fundamental and harmonics with various crystal scattering geometries: Bragg-Bragg, Laue-Bragg, Laue-Lauel. The comparison of the Bragg and Laue case diffraction geometries was done to determine scattering volume effects. Comparisons with dynamical theory calculations will be discussed. These measurements have been carried out in order to assess the level of harmonic contamination which will be present from a double crystal monochromator being designed for the X17 Superconducting Wiggler Beamline

Guiding hard x rays with glass polycapillary fiber

X rays can be guided through a polycapillary fiber by multiple total reflections from the smooth channel walls of the fiber. Using monochromatic Synchrotron Radiation at energies of 22 and 44 keV, we measured the efficiency of transmission of x rays through polycapillary fibers with channel diameters of about 13 {mu}m. Efficiencies of 57.3% and 54.5% for 22 keV and 44 keV x rays, respectively, were obtained with a 120-mm-long straight polycapillary fiber aligned with the incident beam. These values are close to the open fraction of the fiber, which is about 60%. In addition, transmission efficiency was measured as a function of the tilt angle between the incident beam and the axis of the fiber. We also measured the transmission efficiency as a function of the deflection angle for a 114-mm-long curved polycapillary fiber. The measurements are compared with a ray-tracing simulation

Order and strain in main-chain smectic liquid-crystalline polymers and elastomers

The layer correlations in main-chain smectic liquid-crystal polymer and elastomer systems have been studied using high-resolution X-ray scattering. In contrast to side-chain smectic polymers, in main-chain systems the polymer chains are oriented parallel to the layer normal. As a result they couple directly to the lamellar structure and any polymer defect is translated into layer distortions. For the homopolymers the resulting X-ray lineshapes are well described by Lorentzians. This is interpreted as an average of algebraically decaying order in domains with dimensions of hundreds of nm and a wide dispersion of sizes. The elastomers show much broader peaks than the correponding polymers. This is attributed to strong non-uniform strain within the finite-size domains due to defects of the layer structure

CT imaging of small animals using monochromatized synchrotron x rays

Rats and chicken embryos were imaged in vivo with a prototype Multiple Energy Computed Tomography (MECT) system using monochromatized x rays from the X17 superconducting wiggler at the National Synchrotron Light Source. The CT configuration coated of a horizontal low-divergence, fan-shaped beam, 70 mm wide and 0.5 mm high, and a subject rotating about a vertical aids. A linear-array high-purity Ge detector with 140 elements, each 0.5 mm wide and 6 mm thick, was used with a data acquisition system that provides a linear response over almost six orders of magnitude of detector current. The dual photon absorptiometry (DPA) algorithm was applied to images of the rat head acquired at 20 and 45 keV to obtain two new images, one representing the low-Z, and the other the intermediate-Z clement group. The results indicate that the contrast resolution and the quantification accuracy of the images improve stepwise; first, with the monochromatic beam and, second, the DPA method. The system is a prototype for a brain scanner