Wavelength-resolved Neutron Tomography for Crystalline Materials

Abstract

Wavelength-resolved (WR) neutron transmission tomography is an emerging technique to characterize engineering materials. While tomographic reconstruction for amorphous samples is straightforward, it is challenging to reconstruct samples with single-crystal domains because the attenuation of the sample varies as a function of its orientation with respect to the incident beam due to Bragg scattering. In this paper, we present an algorithm that can reconstruct samples with single-crystal domains from WR neutron tomographic measurements. In particular, we use a model-based iterative reconstruction (MBIR) technique that reconstructs the volume by identifying and leaving out the regions of the measurement that are affected by Bragg scatter. We combine the output of the MBIR method with an algorithm that matches the reconstruction to the identified Bragg scatter to reconstruct a feature that corresponds to the local crystallography of the sample being measured. Using simulated data, we demonstrate how our algorithm can reconstruct materials with single-crystal domains, thereby adding a powerful new capability for WR neutron imaging instruments.

Bragg-edge attenuation spectra at voxel level from 4D wavelength-resolved neutron tomography

“…Assuming an isotropic orientation distribution along the beam direction of the crystal grains in a polycrystalline material, the filtered back projection algorithm may be applied for tomographic reconstruction (Woracek et al, 2014). In the case of single crystals (Venkatakrishnan et al, 2019) or strain tomography (Abbey et al, 2009;Wensrich et al, 2016b;Hendriks et al, 2017), where the anisotropy of the probed characteristics has to be considered, iterative techniques with specific boundary conditions have been implemented to address the tomographic reconstruction.…”