Abstract
Neutron dark-field imaging is a powerful tool for the spatially resolved characterization of microstructural features of materials and components. Recently, a novel achromatic technique based on a single absorption grating for the concurrent measurement of attenuation, dark-field and differential phase contrast was introduced. However, the range of measurable length scales of the technique in quantitative dark-field measurements appeared limited to some 10–100 nanometers, due to the relatively high spatial resolution requirement to detect the projected beam modulation. Here, we show how using grating–detector distances beyond the resolution limit for a given collimation produces a sequence of inverse and regular projection patterns and, thus, leads to a significant extension of the range of accessible length scales probed by dark-field imaging. In addition, we show that this concept can also be applied to 2D grating structures, which will enable concurrent three-fold directional dark-field measurements at a wide range of length scales. The approach is demonstrated with measurements on an electrical steel sheet sample, which confirm the validity of combining the results from the regular and inverse grating patterns.
Highlights
Advanced and multimodal imaging techniques with neutrons and X-rays that go beyond conventional attenuation contrast imaging have recently experienced a rapid growth in applications
We demonstrated a non-interferometric inverse projection pattern regime in the far field of regular non-diffractive absorption gratings
We show that this regime can be utilized to significantly extend the range of correlation lengths probed with single grating dark-field contrast imaging
Summary
Advanced and multimodal imaging techniques with neutrons and X-rays that go beyond conventional attenuation contrast imaging have recently experienced a rapid growth in applications. Compared to the conventional attenuation signal, X-ray phase contrast imaging can provide significantly better contrast for visualizing small electron density variations in a sample, and it has shown potential for dose reduction, which is important for clinical applications [1,2]. The feasibility of phase contrast imaging has been demonstrated for neutrons and applied for mapping phase shifts induced by bulk materials [3,4], and by magnetic fields [5,6]. Grating interferometry (GI) is the most efficient technique for this multimodal imaging approach that delivers both the phase contrast and the dark-field signals in addition to the attenuation. It is based on measuring the local modulation of an interference pattern induced in the beam by the grating interferometer. A conventional neutron GI setup is typically comprised of a set of three line gratings with defined periods, typically on the order from a few to a few tens of micrometers, which produce an interference pattern through the Talbot–Lau effect
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