Development of powder diffraction apparatus for small-angle X-ray scattering measurements

Fast X-ray diffraction (XRD) tomography for enhanced identification of materials

X-ray computed tomography (CT) is a commercially established modality for imaging large objects like passenger luggage. CT can provide the density and the effective atomic number, which is not always sufficient to identify threats like explosives and narcotics, since they can have a similar composition to benign plastics, glass, or light metals. In these cases, X-ray diffraction (XRD) may be better suited to distinguish the threats. Unfortunately, the diffracted photon flux is typically much weaker than the transmitted one. Measurement of quality XRD data is therefore slower compared to CT, which is an economic challenge for potential customers like airports. In this article we numerically analyze a novel low-cost scanner design which captures CT and XRD signals simultaneously, and uses the least possible collimation to maximize the flux. To simulate a realistic instrument, we propose a forward model that includes the resolution-limiting effects of the polychromatic spectrum, the detector, and all the finite-size geometric factors. We then show how to reconstruct XRD patterns from a large phantom with multiple diffracting objects. We include a reasonable amount of photon counting noise (Poisson statistics), as well as measurement bias (incoherent scattering). Our XRD reconstruction adds material-specific information, albeit at a low resolution, to the already existing CT image, thus improving threat detection. Our theoretical model is implemented in GPU (Graphics Processing Unit) accelerated software which can be used to further optimize scanner designs for applications in security, healthcare, and manufacturing quality control.

High-performance small- and wide-angle X-ray scattering (SAXS/WAXS) experiments on a multi-functional laboratory goniometer platform with easily exchangeable X-ray modules

Small-angle X-ray scattering (SAXS) is a well-established, versatile technique for the analysis of nanoscale structures and dimensions, e.g., in liquid dispersions, thin solid objects or powder samples. When combined with wide-angle X-ray scattering (WAXS), complementary information about the atomic structure can be obtained. SAXS experiments traditionally require dedicated instruments to achieve the desired angular resolution, sensitivity, stability, and speed of measurement. Here we demonstrate how a multi-functional laboratory goniometer platform, as widely being used for powder X-ray diffraction and for a variety of related techniques, can be configured with pre-aligned X-ray modules that enable advanced SAXS/WAXS experiments, without compromising the exceptional versatility of the instrument. Line and point collimation setups, as well as quick and easy switching between them, are readily possible. Key components are a detachable, evacuated beam path and a high-resolution, low-noise hybrid pixel area detector, in combination with a hardware interface design that allows to configure the instrument with different X-ray modules without the need for re-alignment. Software for SAXS data reduction and analysis was developed. The good SAXS/WAXS performance and the derived analytical results were verified on various test samples, such as gold nanoparticles, colloidal silica, liposomes, dilute protein solutions, and solid polymer samples. It is believed that this novel approach to SAXS/WAXS instrumentation will help to make this powerful structure analysis technique more widely accessible and affordable for multi-user laboratories.