Autonomous Polycrystalline Material Decomposition for Hyperspectral Neutron Tomography

Hyperspectral neutron tomography is an effective method for analyzing crystalline material samples with complex compositions in a non-destructive manner. Since the counts in the hyperspectral neutron radiographs directly depend on the neutron cross-sections, materials may exhibit contrasting neutron responses across wavelengths. Therefore, it is possible to extract the unique signatures associated with each material and use them to separate the crystalline phases simultaneously. We introduce an autonomous material decomposition (AMD) algorithm to automatically characterize and localize polycrystalline structures using Bragg edges with contrasting neutron responses from hyperspectral data. The algorithm estimates the linear attenuation coefficient spectra from the measured radiographs and then uses these spectra to perform polycrystalline material decomposition and reconstructs 3D material volumes to localize materials in the spatial domain. Our results demonstrate that the method can accurately estimate both the linear attenuation coefficient spectra and associated reconstructions on both simulated and experimental neutron data

Porosity detection in electron beam-melted Ti-6Al-4V using high-resolution neutron imaging and grating-based interferometry

© 2017, Springer International Publishing Switzerland. A high-resolution neutron tomography system and a grating-based interferometer are used to explore electron beam-melted titanium test objects. The high-resolution neutron tomography system (attenuation-based imaging) has a pixel size of 6.4 µm, appropriate for detecting voids near 25 µm over a (1.5 cm)3 volume. The neutron interferometer provides dark-field (small-angle scattering) images with a pixel size of 30 µm. Moreover, the interferometer can be tuned to a scattering length, in this case, 1.97 µm, with a field-of-view of (6 cm)3. The combination of high-resolution imaging with grating-based interferometry provides a way for nondestructive testing of defective titanium samples. A chimney-like pore structure was discovered in the attenuation and dark-field images along one face of an electron beam-melted (EBM) Ti-6Al-4V cube. Tomographic reconstructions of the titanium samples are utilized as a source for a binary volume and for skeletonization of the pores. The dark-field volume shows features with dimensions near and smaller than the interferometer auto-correlation scattering length

Flexible sample environment for high resolution neutron imaging at high temperatures in controlled atmosphere

High material penetration by neutrons allows for experiments using sophisticated sample environments providing complex conditions. Thus, neutron imaging holds potential for performing in situ nondestructive measurements on large samples or even full technological systems, which are not possible with any other technique. This paper presents a new sample environment for in situ high resolution neutron imaging experiments at temperatures from room temperature up to 1100 °C and/or using controllable flow of reactive atmospheres. The design also offers the possibility to directly combine imaging with diffraction measurements. Design, special features, and specification of the furnace are described. In addition, examples of experiments successfully performed at various neutron facilities with the furnace, as well as examples of possible applications are presented. This covers a broad field of research from fundamental to technological investigations of various types of materials and components

Quantification of Water Absorption and Transport in Parchment

AbstractNeutron radiography was utilized to quantify water absorption and desorption in parchment at the High Flux Isotope Reactor CG-1D imaging facility at Oak Ridge National Laboratory (ORNL). Sequential 60s radiographs of sections of a 15th century parchment were taken as the parchment underwent wetting and drying cycles. This provided time-resolved visualization and quantification of water absorption and transport in parchment

In-situ neutron imaging of hydrogenous fuels in combustion generated porous carbons under dynamic and steady state pressure conditions

We report results from experiments where we characterize the surface properties of soot particlesinteracting with high-pressure methane. We find considerable differences in behavior of the soot materialbetween static and dynamic pressure conditions that can be explained by multiscale correlations inthe dynamics, from the micro to macro of the porous fractal-like carbon matrix. The measurements werepossible utilizing cold neutron imaging of methane mixed with combustion generated carbon (soot)inside steel cells. The studies were performed under static and dynamic pressure conditions in the range10e90 bar, and are of interest for applications of energy storage of hydrogenous fuels. The very high crosssections for neutrons compared to hard X-ray photons, enabled us to find considerable amounts of nativehydrogen in the soot and to see and quantify the presence of hydrogen atoms in the carbon soot matrixunder different pressure conditions. This work lays the base for more detailed in-situ investigations onthe interaction of porous carbon materials with hydrogen in practical environments for hydrogen andmethane storage

Neutron imaging and applications: a reference for the imaging community

Offers an introduction to the basics of neutron beam production in addition to the wide scope of techniques that enhance imaging application capabilities. This title features a section that describes imaging single grains in polycrystalline materials, neutron imaging of geological materials and other materials science and engineering areas

Dynamics of hydrogen loss and structural changes in pyrolyzing biomass utilizing neutron imaging

We present results from neutron-imaging studies of slow, vacuum pyrolysis of beech, poplar and conifer wood, and pelletized biomass from room temperature up to 1000 °C. A detailed and quantitative method to extract 2D (in situ neutron radiography, NR) and 3D (ex situ neutron computed tomography, NCT) information on structural transformation and elemental hydrogen content has been developed. NCT and X-ray tomography (XCT) experiments on a carbonized beech twig permitted comparison of the spatial distribution of hydrogen, better sensed by NCT, and carbon, oxygen, and heavier elements, better sensed by XCT. We have developed a methodology to directly compare structure and hydrogen-loss dynamics measured using neutron imaging with thermogravimetric analysis and differential thermogravimetry and thus can better understand the correlations between hydrogen and carbon release dynamics. While the methodology has been developed for the carbonization of biomass, we expect that it could be applied to in situ dynamic monitoring of other hydrogenous reacting systems with the appropriate spatial and temporal scales

In situ monitoring of hydrogen loss during pyrolysis of wood by neutron imaging

Hydrogen is an element of fundamental importance for energy but hard to quantify in bulk materials. Neutron radiography was used to map . in situ loss of elemental hydrogen from beech tree wood samples during pyrolysis. The samples consisted of three wood cylinders (finished dowel or cut branch) of approximately 1 cm in length. The samples were pyrolyzed under vacuum in a furnace vessel that was placed inside a cold neutron imaging beamline using a temperature ramp of 5 °C/min from ambient up to 400 °C. Neutron radiographs with exposures of 30 s were sequentially recorded with a charge-coupled device over the course of the experiment. Relative absorbance/scattering of the neutron beam by each sample was based on intensity (or brightness) values as a function of pixel position. The much larger neutron cross section for hydrogen compared to carbon and oxygen enables almost direct conversion of neutron attenuation into sample hydrogen content for each time step during the pyrolysis experiment. Target and vessel temperatures were recorded concurrently with collection of the radiographs so that changes could be directly correlated to different states of pyrolysis. The most visible change appeared at the initial phase of the 400 °C plateau as evidenced by strong hydrogen loss and primarily diametric shrinking of the samples. The loss of elemental hydrogen between initial and final states of pyrolysis was estimated to be about 70%

Non-destructive characterization of advanced nuclear fuel materials using neutron imaging

Attenuation-based neutron computed tomography (CT) has been used to non-destructively characterize the uncoated tristructural-isotropic (TRISO) nuclear fuel kernels in this work. Particularly, the effect of two different types of carbon blacks (Raven 3500 and Mogul L) on the internal gelation process of UO3-C kernels has been investigated. With 3D reconstructed kernel volumes and digital imaging processing techniques, heterogenous density distributions are mapped in both types of kernels. It is found that the kernels produced with Mogul L are ∼ 20 % denser and ∼ 10 % larger (in equivalent diameter) than the Raven 3500 kernels. Furthermore, less neutron attenuating regions, which are most likely to be carbon agglomerates as scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) results show, are observed in the Mogul L kernels. The size distribution of such carbon agglomerates (ranges from 50 μm to 850 μm with a peak at ∼ 200 μm) has been determined by analyzing the CT data. Furthermore, multiple metrics, including equivalent diameter, surface area, volume, sphericity, have been extracted to evaluate the fuel kernels. This work demonstrates that neutron imaging is an excellent, nondestructive tool to efficiently characterize, understand, and explore fuel materials for nuclear material research and development

Fabrication and experimental evaluation of microstructured 6Li silicate fiber arrays for high spatial resolution neutron imaging

This work presents the fabrication and experimental evaluation of instrumentation designed to enable higher spatial resolution neutron radiography for those performing research at neutron scattering facilities. Herein, we describe a proof-of-concept array of microstructured silicate fibers with  6Li doped cores that shows progress towards a design for μm resolution neutron radiography. The multicore fiber was fabricated by drawing stacked unit elements of Guardian Glass (Nucsafe Inc., Oak Ridge, TN, USA), a  6Li scintillating core glass, and a silicate cladding glass. These structured fibers function as an array of sub-10-μm waveguides for scintillation light. Measurements have shown a significantly increased integrated charge distribution in response to neutrons, and the spatial resolution of the radiographs is described by edge response and line spread functions of 48±4μmand 59±8μm, respectively