Gabrielle G. Long

Ultra-small-angle X-ray scattering at the Advanced Photon Source

The design and operation of a versatile ultra-small-angle X-ray scattering (USAXS) instrument at the Advanced Photon Source (APS) at Argonne National Laboratory are presented. The instrument is optimized for the high brilliance and low emittance of an APS undulator source. It has angular and energy resolutions of the order of 10−4, accurate and repeatable X-ray energy tunability over its operational energy range from 8 to 18 keV, and a dynamic intensity range of 108 to 109, depending on the configuration. It further offers quantitative primary calibration of X-ray scattering cross sections, a scattering vector range from 0.0001 to 1 A−1, and stability and reliability over extended running periods. Its operational configurations include one-dimensional collimated (slit-smeared) USAXS, two-dimensional collimated USAXS and USAXS imaging. A robust data reduction and data analysis package, which was developed in parallel with the instrument, is available and supported at the APS.

Data-Intensive Science in the US DOE: Case Studies and Future Challenges

Given its leading role in high-performance computing for modeling and simulation and its many experimental facilities, the US Department of Energy has a tremendous need for data-intensive science. Locating the challenges and commonalities among three case studies illuminates, in detail, the technical challenges involved in realizing data-intensive science.

Development of ultra‐small‐angle X‐ray scattering–X‐ray photon correlation spectroscopy

This paper describes the development of ultra-small-angle X-ray scattering–X-ray photon correlation spectroscopy (USAXS–XPCS). This technique takes advantage of Bonse–Hart crystal optics and is capable of probing the long-time-scale equilibrium and non-equilibrium dynamics of optically opaque materials with prominent features in a scattering vector range between those of dynamic light scattering and conventional XPCS. Instrumental parameters for optimal coherent-scattering operation are described. Two examples are offered to illustrate the applicability and capability of USAXS–XPCS. The first example concerns the equilibrium dynamics of colloidal dispersions of polystyrene microspheres in glycerol at 10, 15 and 20% volume concentrations. The temporal intensity autocorrelation analysis shows that the relaxation time of the microspheres decays monotonically as the scattering vector increases. The second example concerns the non-equilibrium dynamics of a polymer nanocomposite, for which it is demonstrated that USAXS–XPCS can reveal incipient dynamical changes not observable by other techniques.

Quantitative characterization of the contrast mechanisms of ultra-small-angle X-ray scattering imaging

A general treatment of X-ray imaging contrast for ultra-small-angle X-ray scattering (USAXS) imaging is presented; this approach makes use of phase propagation and dynamical diffraction theory to account quantitatively for the intensity distribution at the detector plane. Simulated results from a model system of micrometer-sized spherical SiO{sub 2} particles embedded in a polypropylene matrix show good agreement with experimental measurements. Simulations by means of a separate geometrical ray-tracing method also account for the features in the USAXS images and offer a complementary view of small-angle X-ray scattering as a contrast mechanism. The ray-tracing analysis indicates that refraction, in the form of Porod scattering, and, to a much lesser extent, X-ray reflection account for the USAXS imaging contrast.

Applications of Laminar Weak-Link Mechanisms for Ultraprecision Synchrotron Radiation Instruments

Unlike traditional kinematic flexure mechanisms, laminar overconstrained weak‐link mechanisms provide much higher structure stiffness and stability. Using a laminar structure configured and manufactured by chemical etching and lithography techniques, we are able to design and build linear and rotary weak‐link mechanisms with ultrahigh positioning sensitivity and stability for synchrotron radiation applications. Applications of laminar rotary weak‐link mechanism include: high‐energy‐resolution monochromators for inelastic x‐ray scattering and x‐ray analyzers for ultra‐small‐angle scattering and powder‐diffraction experiments. Applications of laminar linear weak‐link mechanism include high‐stiffness piezo‐driven stages with subnanometer resolution for an x‐ray microscope. In this paper, we summarize the recent designs and applications of the laminar weak‐link mechanisms at the Advanced Photon Source.

Facility Update: APS Operations and New Beamlines

The Advanced Photon Source (APS) had an excellent year in 2005 in terms of reliability, availability, and machine development. The accelerator operated for more than 5000 hours, with an availabilit...

Facility update: Research and Operations at the Advanced Photon Source

The Advanced Photon Source (APS) looks forward to a period of growth in the coming years. Meanwhile, in April 2006, the APS reorganized its divisions, creating an X-ray Science Division (XSD), bringing science at the APS on a par with the accelerator, and sharing engineering and support services. The machine division, the Accelerator Systems Division, now includes all of the groups that operate and develop the machine and focus on future accelerator research.

Versatile Collimating Crystal Stage for a Bonse‐Hart USAXS Instrument

An advanced ultra‐small‐angle X‐ray scattering (USAXS) instrument, using the Bonse‐Hart design and installed at APS, is a robust and reliable instrument, providing a scattering vector (q) range of nearly 4 decades (0.00015 to 1 A−1), an intensity dynamic range of up to 9 decades, standard‐less absolute intensity calibration, and USAXS imaging capabilities. This type of instrument typically uses channel‐cut crystals in both the collimating (before sample) and analyzing (after sample) stages. The optical surfaces of these crystals are finished by etching processes, which leave an orange‐peel surface texture, which would compromise the USAXS imaging quality. Therefore optics with highly polished surfaces using separated crystals in both collimating and analyzing stages were developed. A novel design of the optics and mechanical stage uses a fixed gap between the two separated collimating crystals in which a triangular section of the first crystal is removed, allowing for a variable number (1, 2, 4, 6, or 8) of crystal reflections for X‐ray energies between 7 and 19 keV. The number of reflections is selected by lateral translation of the collimating crystal pair. Rotational alignment of the second crystal in the pair by an artificial channel‐cut crystal mechanism, implemented with a novel high‐stiffness weak link actuated by both a picomotor and a piezo‐electric transducer, provides the capability to align or adjust an assembly of crystals to achieve the same performance as a single channel‐cut crystal with integral weak link. The arrangement of both crystals is held on a removable base that can be remounted with precision within the Si(111) rocking curve on a three‐point kinematic mount. Additional tilt adjustments are also provided for initial alignment. This monochromator has proven to be highly robust with respect to motions and vibrations, as well as flexible with respect to selection of number of reflections, and its performance directly resulted in the highly reliable performance of the whole USAXS instrument.An advanced ultra‐small‐angle X‐ray scattering (USAXS) instrument, using the Bonse‐Hart design and installed at APS, is a robust and reliable instrument, providing a scattering vector (q) range of nearly 4 decades (0.00015 to 1 A−1), an intensity dynamic range of up to 9 decades, standard‐less absolute intensity calibration, and USAXS imaging capabilities. This type of instrument typically uses channel‐cut crystals in both the collimating (before sample) and analyzing (after sample) stages. The optical surfaces of these crystals are finished by etching processes, which leave an orange‐peel surface texture, which would compromise the USAXS imaging quality. Therefore optics with highly polished surfaces using separated crystals in both collimating and analyzing stages were developed. A novel design of the optics and mechanical stage uses a fixed gap between the two separated collimating crystals in which a triangular section of the first crystal is removed, allowing for a variable number (1, 2, 4, 6, or 8) ...