X-rays and neutrons provide complementary non-destructive probes for the analysis of structure and chemical
composition of materials. Contrast differences between the modes arise due to the differences in interaction with matter.
Due to the high sensitivity to hydrogen, neutrons excel at separating liquid water or hydrogenous phases from the
underlying structure while X-rays resolve the solid structure. Many samples of interest, such as fluid flow in porous
materials or curing concrete, are stochastic or slowly changing with time which makes analysis of sequential imaging
with X-rays and neutrons difficult as the sample may change between scans. To alleviate this issue, NIST has developed
a system for simultaneous X-ray and neutron tomography by orienting a 90 keVpeak micro-focus X-ray tube orthogonally
to a thermal neutron beam. This system allows for non-destructive, multimodal tomography of dynamic or stochastic
samples while penetrating through sample environment equipment such as pressure and flow vessels. Current efforts are
underway to develop methods for 2D histogram based segmentation of reconstructed volumes. By leveraging the
contrast differences between X-rays and neutrons, greater histogram peak separation can occur in 2D vs 1D enabling
improved material identification.
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