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ME-EM Graduate Seminar Speaker Series

proudly presents:

Dr. Daniel Hussey
National Institute of Standards and Technology

Abstract: This talk will provide an overview of NIST’s current neutron imaging development efforts. Neutrons provide a unique view into materials since they are electrically neutral and interact primarily via the strong nuclear force. In particular, neutrons readily penetrate common metals (aluminum, steel, etc.) yet scatter strongly from hydrogen (water, oil, etc.). As a result, neutron imaging has been widely used to study water transport phenomena in hydrogen fuel cells. In order to provide more detailed images of the water content in fuel cells, NIST has continually developed neutron imaging detectors to improve the achievable spatial resolution, currently about 1.5 μm [1]. To fully exploit the unique view that neutrons provide, NIST has developed a combined neutron, x‐ray tomography system which acquires 3D views of a complex system with both probes simultaneously [2]. With two wildly different interactions, one can develop a more accurate representation of a complex structure such as curing or degrading concrete. While neutron attenuation images provide insight into hydrogenous systems, neutron phase imaging with a grating interferometer provides additional contrast mechanisms via material density gradients or dispersion of the microstructure [3]. One can tune the length scale of the interferometer so as to measure average pore radii from 1 nm to ~10 μm with a pixel pitch ~100 μm to create multi‐scale images even as a tomogram. Such dark‐field images can reveal the distribution of the pore network in geological systems or how porosity evolves during fatigue testing of metal printed stainless steel [4]. Finally, for crystalline materials, one can measure so‐called “Bragg Edges” (the wavelength above which a lattice plane can no longer Bragg scatter resulting in an increase in transmission) to map out either crystal phases in TRIP steels or lattice strains in welds [5].

References:

[1] D.S. Hussey et al., Nuclear Inst. and Methods in Physics Research, A 866 (2017) 9–12.
[2] J.M. LaManna et al., Review of Scientific Instruments 88, 113702 (2017).
[3] Pushin et al., Physical Review A 95, 043637 (2017); D. Sarenac et al., Physical Review Letters 120, 113201 (2018).
[4] A.J. Brooks, Materials and Design 140 (2018) 420–430.
[5] W. Woo et al, submitted Scripta Materia (2018); J.W. Sowards et al, Journal of Research of the National Institute of Standards and Technology 123, 123011 (2018).

Event Figure 1. Dark-field images of conventional and printed dog bones subjected to torsional fatigue.