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NIST NeXT: a system for truly simultaneous neutron and x-ray tomography

Neutrons and X-rays provide excellent complementary, nondestructive probes to understand internal structure of systems across engineering and material science. With its sensitivity to hydrogen, neutrons excel at separating fluids, such as water or oil, from solid and gas phases in three-phase systems whereas X-rays excel at identifying the solid phase. To fully leverage the complementarity of the two methods, the National Institute of Standards and Technology (NIST) has developed the Neutron and X-ray Tomography (NeXT) system which orients a microfocus X-ray generator orthogonally to a reactor sourced thermal neutron beam. This orientation allows for truly simultaneous acquisition of both modalities so that the multi-modal data sets of samples that are evolving with time or undergoing stochastic processes can be directly correlated. The NeXT system has been available for external researchers since 2015 through the NIST Center for Neutron Research user facility program. Significant efforts have resulted in distributable software packages to facilitate image denoising, tomography reconstruction, volume registration, and bivariate histogram segmentation. This paper will give an overview of the NeXT system, explain the process for bivariate histogram segmentation, and provide several examples of use cases for the system.