Imaging Regions of Sub-Resolution Particles Using Gratings-Based Phase Contrast X-ray Imaging

Abstract:

X-ray tomography is an important noninvasive tool for characterizing the structural features of many materials, including soils. Spatial resolution is typically limited to ~10 μm voxels for lab-based systems and ~1 μm voxels for many synchrotron-based systems. However, many properties relevant to aqueous-phase reactive transport in natural systems take place at finer length scales. Recent developments in x-ray imaging, such as phase contrast imaging, have indicated that the use of a patterning element (such as a grating) in the beam can allow measurement of small-angle elastic scattering, which can be used to detect regions that include sub-resolution particles while still providing a 3-D image with a large field of view. We investigated the use of gratings-based phase contrast x-ray imaging for identifying regions containing sub-resolution particles. Investigations of model materials with controlled size distributions, and of natural materials, showed that regions including clay minerals could be distinguished within analyzed volumes. We also investigated procedures for tuning the measurement system to optimize the sensitivity to specific length scales. The use of a patterning element presents a useful extension to conventional x-ray imaging, which will aid in the characterization of unresolved porous regions in soils and other materials.