P. Jemian

Irena: tool suite for modeling and analysis of small-angle scattering

Irena, a tool suite for analysis of both X-ray and neutron small-angle scattering (SAS) data within the commercial Igor Pro application, brings together a comprehensive suite of tools useful for investigations in materials science, physics, chemistry, polymer science and other fields. In addition to Guinier and Porod fits, the suite combines a variety of advanced SAS data evaluation tools for the modeling of size distribution in the dilute limit using maximum entropy and other methods, dilute limit small-angle scattering from multiple non-interacting populations of scatterers, the pair-distance distribution function, a unified fit, the Debye–Bueche model, the reflectivity (X-ray and neutron) using Parratts formalism, and small-angle diffraction. There are also a number of support tools, such as a data import/export tool supporting a broad sampling of common data formats, a data modification tool, a presentation-quality graphics tool optimized for small-angle scattering data, and a neutron and X-ray scattering contrast calculator. These tools are brought together into one suite with consistent interfaces and functionality. The suite allows robust automated note recording and saving of parameters during export.

Ultra-Small-Angle X-ray Scattering Instrument at the Advanced Photon Source: History, Recent Development, and Current Status

The 25-year history and development of an ultra-small-angle X-ray scattering (USAXS) instrument dedicated to serving materials research is presented and discussed. The instrument’s successful track record is attributed to three factors. The first, and surely the most important, is that all development has been driven by scientific research directions and opportunities. Second, the USAXS instrument is a core capability rather than an add-on facility, with measurement capability from micrometers to nanometers, which is precisely the size range where microstructures determine physical properties. The third is that the instrument’s range of capabilities has continually expanded, now including 2D collimation, imaging, and dynamics. And finally, USAXS has enjoyed the benefit of a management structure that has consistently appreciated the unique experimental measurement capabilities that USAXS delivers.

The effect of the shape function on small-angle scattering analysis by the maximum entropy method

Analysis of small-angle scattering data to obtain a particle-size distribution is dependent upon the shape function used to model the scattering. From a maximum-entropy analysis of small-angle scattering data, the effect of shape-function selection on the obtained size distribution is demonstrated using three different shape functions to describe the same scattering data from each of two alloys. The alloys have been revealed by electron microscopy to contain a distribution of randomly oriented and mainly noninteracting irregular ellipsoidal precipitates. A comparison is made between the different forms of the shape function. The effect of an incident-wavelength distribution is also shown. The importance of testing appropriate shape functions and validating these against other microstructural studies is discussed.

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.

Firmware lower-level discrimination and compression applied to streaming x-ray photon correlation spectroscopy area-detector data

We present a data acquisition system to perform on-the-fly background subtraction and lower-level discrimination compression of streaming x-ray photon correlation spectroscopy data from a fast charge-coupled device (CCD) area detector. The system is built using a commercial frame grabber with an on-board field-programmable gate array. The system is capable of continuously processing at least 60 CCD frames per second each consisting of 1024 × 1024 16-bit pixels with ≲ 15,000 photon hits per frame at a maximum compression factor of ≈95%.

FPGA-based compression of streaming x-ray photon correlation spectroscopy data

A data acquisition system to perform real-time background subtraction and lower-level-discrimination-based compression of streaming x-ray photon correlation spectroscopy (XPCS) data from a fast charge-coupled device (CCD) area detector has been built and put into service at the Advanced Photon source (APS) at Argonne National Laboratory. A commercial frame grabber with on-board field-programmable gate array (FPGA) was used in the design, and continuously processes 60 frames per second each consisting of 1,024 × 1,024 pixels with up to 64512 photon hits per frame.

Mechanical Design of a High-Resolution X-ray Powder Diffractometer at the Advanced Photon Source

A novel high-resolution x-ray powder diffractometer has been designed and commissioned at the bending magnet beamline 11-BM at the Advanced Photon Source (APS), Argonne National Laboratory (ANL). This state-of-the-art instrument is designed to meet challenging mechanical and optical specifications for producing high-quality powder diffraction data with high throughput. The 2600 mm (H) X 2100 mm (L) X 1700 mm (W) diffractometer consists of five subassemblies: a customized two-circle goniometer with a 3-D adjustable supporting base; a twelve-channel high-resolution crystal analyzer system with an array of precision x-ray slits; a manipulator system for a twelve scintillator x-ray detectors; a 4-D sample manipulator with cryo-cooling capability; and a robot-based sample exchange automation system. The mechanical design of the diffractometer as well as the test results of its positioning performance are presented in this paper.

2006 XSD Scientific Software Workshop report.

In May of 2006, a committee was formed to assess the fundamental needs and opportunities in scientific software for x-ray data reduction, analysis, modeling, and simulation. This committee held a series of discussions throughout the summer, conducted a poll of the members of the x-ray community, and held a workshop. This report details the findings and recommendations of the committee. Each experiment performed at the APS requires three crucial ingredients: the powerful x-ray source, an optimized instrument to perform measurements, and computer software to acquire, visualize, and analyze the experimental observations. While the APS has invested significant resources in the accelerator, investment in other areas such as scientific software for data analysis and visualization has lagged behind. This has led to the adoption of a wide variety of software with variable levels of usability. In order to maximize the scientific output of the APS, it is essential to support the broad development of real-time analysis and data visualization software. As scientists attack problems of increasing sophistication and deal with larger and more complex data sets, software is playing an ever more important role. Furthermore, our need for excellent and flexible scientific software can only be expected to increase, as the upgrade of the APS facility and the implementation of advanced detectors create a host of new measurement capabilities. New software analysis tools must be developed to take full advantage of these capabilities. It is critical that the APS take the lead in software development and the implementation of theory to software to ensure the continued success of this facility. The topics described in this report are relevant to the APS today and critical for the APS upgrade plan. Implementing these recommendations will have a positive impact on the scientific productivity of the APS today and will be even more critical in the future.

EPICS-based control and data acquisition for the APS slope profiler(Conference Presentation)

The motion control, data acquisition and analysis system for APS Slope Measuring Profiler was implemented using the Experimental Physics and Industrial Control System (EPICS). EPICS was designed as a framework with software tools and applications that provide a software infrastructure used in building distributed control systems to operate devices such as particle accelerators, large experiments and major telescopes. EPICS was chosen to implement the APS Slope Measuring Profiler because it is also applicable to single purpose systems. The control and data handling capability available in the EPICS framework provides the basic functionality needed for high precision X-ray mirror measurement. Those built in capabilities include hardware integration of high-performance motion control systems (3-axis gantry and tip-tilt stages), mirror measurement devices (autocollimator, laser spot camera) and temperature sensors. Scanning the mirror and taking measurements was accomplished with an EPICS feature (the sscan record) which synchronizes motor positioning with measurement triggers and data storage. Various mirror scanning modes were automatically configured using EPICS built-in scripting. EPICS tools also provide low-level image processing (areaDetector). Operation screens were created using EPICS-aware GUI screen development tools.

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) ...