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The Oak Ridge National Laboratory is planning to build the Second Target Station (STS) at the Spallation Neutron Source (SNS). STS will host a suite of novel instruments that complement the First Target Station’s beamline capabilities by offering an increased flux for cold neutrons and a broader wavelength bandwidth. A novel neutron imaging beamline, named the Complex, Unique, and Powerful Imaging Instrument for Dynamics (CUPI2D), is among the first eight instruments that will be commissioned at STS as part of the construction project. CUPI2D is designed for a broad range of neutron imaging scientific applications, such as energy storage and conversion (batteries and fuel cells), materials science and engineering (additive manufacturing, superalloys, and archaeometry), nuclear materials (novel cladding materials, nuclear fuel, and moderators), cementitious materials, biology/medical/dental applications (regenerative medicine and cancer), and life sciences (plant–soil interactions and nutrient dynamics). The innovation of this instrument lies in the utilization of a high flux of wavelength-separated cold neutrons to perform real time in situ neutron grating interferometry and Bragg edge imaging—with a wavelength resolution of δλ/λ ≈ 0.3%—simultaneously when required, across a broad range of length and time scales. This manuscript briefly describes the science enabled at CUPI2D based on its unique capabilities. The preliminary beamline performance, a design concept, and future development requirements are also presented.

X-ray beams with orbital angular momentum (OAM) are a promising tool for x-ray characterization techniques. Beams with OAM have a helicity--an azimuthally varying phase--which leads to a gradient of the light field. New material properties can be probed by utilizing the helicity of an OAM beam. Here, we demonstrate a novel dichroic effect in resonant diffraction from an artificial antiferromagnet with a topological defect. We found that the scattered OAM beam has circular dichroism at the antiferromagnetic Bragg peak whose sign is coupled to its helicity, which reveals the real-space configuration of the antiferromagnetic ground state. Thermal cycling of the artificial antiferromagnet can change the ground state, as indicated by reversal of the sign of circular dichroism. This result is one of the first demonstrations of a soft x-ray spectroscopy characterization technique utilizing the OAM of x-rays. This helicity-dependent circular dichroism exemplifies the potential to utilize OAM beams to probe matter in a way that is inaccessible using currently available x-ray techniques.

Electron beam melting (EBM) is one of the constantly developing powder bed fusion (PBF) additive manufacturing technologies (AM) offering advanced control over the manufacturing process. Development of the additive manufacturing today is targeting both widening of the available materials classes, and introducing new manufacturing modalities. Present research is related to the new possibilities in tailoring different properties within additively manufactured components effectively adding “fourth dimension to the 3D-printing”. Through manipulating beam energy deposition (scanning strategy) it is possible to tailor quite different material properties selectively within each manufactured component, including crystalline and amorphous state, effective material density, as well as mechanical, thermal, electrical and acoustic properties. With the blends of precursor powder, it is also possible to acquire by choice both metal-metal composite and completely alloyed material. Specific examples are given in relation to the EBM, but majority of the conclusions are valid for the other PBF techniques as well.

Migration of water and ions dissolved in water through concrete is of interest in civil engineering. In particular, the behavior of radionuclides dissolved in water is of great interest to the nuclear industry because significant numbers of nuclear structures contain large amounts of concrete, acting as a barrier to radionuclides against entering the environment. Study of the migration of water molecules and ions in concrete hitherto required destructive chemical analysis. In this work, we present a non-destructive probe to investigate the uptake of uranium, iodine and water into mortar in situ using a time-of-flight neutron imaging method that allows selecting different neutron energies, providing elemental sensitivity in the analysis of the absorption process. First results indicate that water molecules are the fastest migrating species while iodine is significantly slower, and uranium was not observed to migrate through the structure within the time frame of the experiment and furthermore blocks the migration of water.

A synergic combination of neutron techniques was applied to characterize non-invasively the laminated structure of a set of ancient katana, part of the East Asian Collection of the Museum of Applied Arts and Sciences (MAAS) in Sydney. Neutron tomography, diffraction, residual stress and Bragg-edge transmission analyses were undertaken on samples of well-known origin, time period and authorship to create a reference database on the main manufacturing methods developed by Japanese swordsmiths. In the attempt to attributemumei(no-signature) blades basing on a scientific analytical method rather than a stylistic analysis, data from the reference samples were benchmarked against the results obtained from the unknown blade to identify differences and commonalities in the production process.

Energy-resolved neutron imaging is employed for in-situ measurements of dopant transport in a simple experiment performed before the crystal growth of the scintillator BaBrCl:5%Eu via a vertical gradient freeze technique. During a stabilization period preceding growth, we observed the diffusion of Eu from the solid phase into the melt over a period of approximately 4 hours. Comparing the measured centerline concentration profile with a mathematical model for the system, we estimate the solid-state diffusivity of Eu in BaBrCl as D 1 = 1.9 × 10 − 10 m2/s and an upper limit for the liquid-phase diffusivity of Eu in the melt as D 2 * = 2.5 × 10 − 10 m2/s, at temperatures near the melting point. We compare this experiment, where diffusion is driven by a concentration discontinuity arising from segregation, to the classical diffusion couple technique. Suggestions are offered on how this segregation-driven couple might be improved as a tool for measuring diffusion coefficients, and we draw attention to the great promise of neutron imaging for in-situ measurements of the distribution of elements, with sufficiently high neutron attenuation coefficients, in difficult environments.

Methods for postirradiation characterization of bulk (cm3) irradiated materials or even spent nuclear fuels are sparse due to their extremely radioactive nature. While several methods exist to characterize smaller volumes (

The capability of neutrons to penetrate materials opaque to other non-destructive techniques combined with relatively high neutron attenuation cross section for hydrogen provide unique possibilities to reveal internal distribution of water and other hydrogen-containing substances in various bulky samples. In this study we compare the accuracy of water thickness reconstruction from two types of neutron imaging experiments: neutron radiography with a white beam spectrum and energy-resolved neutron imaging. Neutron transmission spectra available at the latter modality can be used for the extraction of certain material characteristics, such as microstructure and elemental composition, usually not accessible for the analysis of images integrated over the entire neutron spectrum. Distribution of water within the sample, however, can be reconstructed from both types of neutron imaging methods. The results of present study indicate that the accuracy of water mapping appeared to be comparable within the 2%–4% error in our experiments dominated by non-optimized calibration of background signal. The accuracy of water thickness reconstruction was verified with a calibration step wedge sample for both imaging modalities. We also demonstrate the applicability of this technique for the studies of water absorptivity and porosity of ancient Roman concrete samples extracted from Cosa and Portus Traiani sites. These reconstruction methods are not only limited to quantification of water or hydrogen containing substances, but can be implemented to any other material with relatively high neutron attenuation.

This paper presents a series of experiments to characterize the performance of the new IMAT beamline at the ISIS pulsed neutron source and provides examples to showcase the potential applications of Bragg-edge transmission imaging on the instrument. The characterization includes determination of the IMAT spectral and spatial resolutions through calibration measurements, and also determination of the precision and the accuracy of Bragg-edge analysis for lattice parameters of ceramics, metals and textured engineering alloys through high-temperature measurements. A novel Bragg-edge analysis method based on the cross-correlation of different Bragg edges has been developed to provide an estimate of the change in lattice parameter, which is especially useful for measurements of textured samples. Three different applications of the Bragg-edge transmission imaging technique are presented, including strain mapping, texture mapping and obtaining crystallographic information, i.e. the dependence on temperature of the Debye–Waller factor. The experimental results demonstrate the ability of the IMAT beamline to provide accurate strain measurements with uncertainties as low as 90 µɛ with reasonable measurement time, while characteristic materials parameters can be mapped across the sample with a spatial resolution of 300–600 µm for a strain map and down to ∼90 µm for a texture map.

Imaging using scintillators is a widespread and cost-effective approach in radiography. While different types of scintillator and sensor configurations exist, it can be stated that the detection efficiency and resolution of a scintillator-based system is strongly depended on the scintillator material and its thickness. Recently developed event-driven detectors are capable of observing spots of light emitted by the scintillator after a particle interaction, allowing to reconstruct the Center-of-Mass of the interaction on the scintillator surface. This results in a more precise location of the event and therefore provides a pathway to overcome the scintillator thickness limitation and increase the effective spatial resolution of the system. Utilizing this principle, we present a detector capable of Time-of-Flight imaging with a flexible field-of-view, ad-hoc binning and re-binning of data based on the requirements of the experiment including the possibility of particle discrimination via the analysis of the event shape in space and time. It is considered that this novel concept might replace regular cameras in neutron imaging detectors as it provides superior detection capabilities with the most recent results providing an increase by a factor 3 in image resolution and an increase by up to a factor of 7.5 in signal-to-noise for thermal neutron imaging.

A momentum resolved resonant inelastic X-ray scattering (qRIXS) experimental station with continuously rotatable spectrometers and parallel detection is designed to operate at different beamlines at synchrotron and free electron laser (FEL) facilities. This endstation, currently located at the Advanced Light Source (ALS), has five emission ports on the experimental chamber for mounting the high-throughput modular soft X-ray spectrometers (MXS) [24]. Coupled to the rotation from the supporting hexapod, the scattered X-rays from 27.5° (forward scattering) to 152.5° (backward scattering) relative to the incident photon beam can be recorded, enabling the momentum-resolved RIXS spectroscopy. The components of this endstation are described in details, and the preliminary RIXS measurements on highly oriented pyrolytic graphite (HOPG) reveal the low energy vibronic excitations from the strong electron-phonon coupling at C K edge around σ* band. The grating upgrade option to enhance the performance at low photon energies is presented and the potential of this spectroscopy is discussed in summary.

Detectors with microchannel plates (MCPs) provide unique capabilities to detect single photons with high spatial (

Bragg edge tomography was carried out on novel, ultra-thick, directional ice templated graphite electrodes for Li-ion battery cells to visualise the distribution of graphite and stable lithiation phases, namely LiC12 and LiC6. The four-dimensional Bragg edge, wavelength-resolved neutron tomography technique allowed the investigation of the crystallographic lithiation states and comparison with the electrode state of charge. The tomographic imaging technique provided insight into the crystallographic changes during de-/lithiation over the electrode thickness by mapping the attenuation curves and Bragg edge parameters with a spatial resolution of approximately 300 &micro, m. This feasibility study was performed on the IMAT beamline at the ISIS pulsed neutron spallation source, UK, and was the first time the 4D Bragg edge tomography method was applied to Li-ion battery electrodes. The utility of the technique was further enhanced by correlation with corresponding X-ray tomography data obtained at the Diamond Light Source, UK.

Neutron Bragg edge imaging enables spatially resolved studies of crystalline features through the exploitation and analysis of Bragg edges in the transmission spectra recorded in each pixel of an imaging detector. Studies with high spectral resolutions, as is required e.g. for high-resolution strain mapping, and with large wavelength ranges have been largely reserved to pulsed neutron sources. This is due to the fact, that the efficiency for high wavelength resolution measurements is significantly higher at short pulse sources. At continuous sources a large fraction of the available neutrons must be sacrificed in order to achieve high wavelength resolution for a relevant bandwidth e.g. through a chopper system. Here we introduce a pulse overlap transmission imaging technique, which is suited to increase the available flux of high wavelength resolution time-of-flight neutron Bragg edge imaging at continuous neutron sources about an order of magnitude. Proof-of-principle measurements utilizing a chopper with a fourfold repeated random slit distribution of eight slits were performed at a thermal neutron beamline. It is demonstrated, that disentanglement of the overlapping pulses is achieved with the correlation theorem for signal processing. Thus, the Bragg edge pattern can be reconstructed from the strongly overlapping Bragg edge spectra recorded and the results demonstrate the feasibility of the technique.

Energy resolved neutron transmission techniques can provide high-resolution images of strain within polycrystalline samples allowing the study of residual strain and stress in engineered components. Strain is estimated from such data by analysing features known as Bragg-edges for which several methods exist. It is important for these methods to provide both accurate estimates of strain and an accurate quantification the associated uncertainty. Our contribution is twofold. First, we present a numerical simulation analysis of these existing methods, which shows that the most accurate estimates of strain are provided by a method that provides inaccurate estimates of certainty. Second, a novel Bayesian non-parametric method for estimating strain from Bragg-edges is presented. The numerical simulation analysis indicates that this method provides both competitive estimates of strain and accurate quantification of certainty, two demonstrations on experimental data are then presented.

The exciton-phonon coupling in highly oriented pyrolytic graphite is studied using resonant inelastic X-ray scattering (RIXS) spectroscopy. With ~ 70 meV energy resolution, multiple low energy excitations associated with coupling to phonons can be clearly resolved in RIXS spectra. Using resonance dependence and the closed form for RIXS cross-section without considering the intermediate state mixing of phonon modes, the dimensionless coupling constant g is determined to be 5 and 0.4, corresponding to the coupling strength of 0.42 eV +/- 40 meV and 0.21 eV +/- 30 meV, for zone center and boundary phonons respectively. The reduced g value for zone-boundary phonon may be related to its double resonance nature., Main text is 20 pages with 4 figures Supplementary information is 10 pages with 3 figures

Artificial spin ices (ASI) have been widely investigated as magnetic metamaterials with exotic properties governed by their geometries. In parallel, interest in X-ray photon orbital angular momentum (OAM) has been rapidly growing. Here we show that a square ASI with a programmed topological defect, a double edge dislocation, imparts OAM to scattered X-rays. Unlike single dislocations, a double dislocation does not introduce magnetic frustration, and the ASI equilibrates to its antiferromagnetic (AF) ground state. The topological charge of the defect differs with respect to the structural and magnetic order; thus, X-ray diffraction from the ASI produces photons with even and odd OAM quantum numbers at the structural and AF Bragg conditions, respectively. The magnetic transitions of the ASI allow the AF OAM beams to be switched on and off by modest variations of temperature and applied magnetic field. These results demonstrate ASIs can serve as metasurfaces for reconfigurable X-ray optics that could enable selective probes of electronic and magnetic properties., Comment: 7 pages, 4 figures

The radiation levels from used nuclear fuel make their post irradiation examination very difficult. Handling material removed from assemblies is almost exclusively performed inside shielded hot cells. Neutron radiography provides a non-destructive option for examining the internal structure, location and integrity of irradiated fuel. This paper addresses the performance and stability of a neutron imaging detector comprised of microchannel plates (MCPs) and a Timepix readout in gamma and neutron radiation environments. The detector is being considered as an alternative to the currently used activation foils and photographic film measurement techniques. The MCP/Timepix detector was used in neutron radiography experiment on a beam line at the Neutron Radiography Reactor (NRAD) at Idaho National Laboratory (INL). The detector was installed ∼ 17.5 m from the reactor core with a line of sight view to the core, which results in a fast and epithermal neutron spectrum as well as high intensity gamma radiation . The gamma-ray dose rate in the beam line was 812 mSv/hr. Complementary measurements were made using 137Cs and 60Co isotopic sources at gamma dose rates in excess of 6 Sv/hr. The detector functioned normally over several hours in this environment. These conditions are comparable to planned radiography of irradiated nuclear fuel assemblies. Experimental results using ASTM sensitivity and beam purity indicators suggest that a spatial resolution of μ m may be possible in neutron radiographic measurements using this detector for studies of irradiated nuclear fuel. Potential radiographic and tomographic applications are discussed. The results of present experiments are not limited to the studies of irradiated fuel assemblies, but rather are relevant to any experiment where imaging needs to be performed in a high radiation environment.

Zr-based alloys are used in nuclear power plants because of a unique combination of very low neutron absorption and excellent mechanical properties and corrosion resistance at operating conditions. However, Hydrogen (H) or Deuterium ingress due to waterside corrosion during operation can embrittle these materials. In particular, Zr alloys are affected by Delayed Hydride Cracking (DHC), a stress-corrosion cracking mechanism operating at very low H content (∼100?300 wt ppm), which involves the diffusion of H to the crack tip. H content in Zr alloys is commonly determined by destructive techniques such as inert gas fusion and vacuum extraction. In this work, we have used neutron imaging to non-destructively quantify the spatial distribution of H in Zr alloys specimens with a resolution of ∼5 wt ppm, an accuracy of ∼10 wt ppm and a spatial resolution of ∼25 μm × 5 mm x 10 mm. Non-destructive experiments performed on a comprehensive set of calibrated specimens of Zircaloy-2 and Zr2.5%Nb at four neutron facilities worldwide show the typical precision and repeatability of the technique. We have observed that the microstructure of the alloy plays an important role on the homogeneity of H across a specimen. We propose several strategies for performing H determinations without calibrated specimens, with the most precise results for neutrons having wavelengths longer than 5.7 Å. Fil: Buitrago Montañez, Nayibe Lucia. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Santisteban, Javier Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Tartaglione, Aureliano. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Marín, J.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Barrow, L.. Queens University; Canadá Fil: Daymond, M. R.. Queens University; Canadá Fil: Schulz, M.. Universitat Technical Zu Munich; Alemania Fil: Grosse, M.. Karlsruher Institut fur Technologie; Alemania Fil: Tremsin, A.. University of California at Berkeley; Estados Unidos Fil: Lehmann, E.. Paul Scherrer Institut; Suiza Fil: Kaestner, A.. Paul Scherrer Institut; Suiza Fil: Kelleher, J.. Rutherford Appleton Laboratory; Reino Unido Fil: Kabra, S.. Rutherford Appleton Laboratory; Reino Unido

This paper presents 2D mapping of residual strains, induced by cold expansion and laser shock peening processing of aluminium alloy samples, by using Bragg edge neutron transmission. Neutron transmission uses information contained in the neutron beam transmitted through a sample. It is shown that neutron transmission strain mapping with high spatial resolution can provide important insights into the distribution of residual strains associated with processing of materials. The residual strain field around a cold-expanded hole can be revealed in detail, as can be the residual strain profile associated with laser peening. Results are correlated with measurements obtained by conventional neutron diffraction and incremental hole drilling. The residual strain variation around the cold-expanded hole and the depth of compressive residual strain generated by the peening process were captured with high spatial resolution, showing the advantages of neutron transmission over other well-established strain measurement methods by non-destructively generating a map of residual strains over a large area. Keywords: Neutron transmission, Residual strain, Strain mapping, Bragg edge analysis, Cold expansion, Laser shock peening

BaBrCl:Eu is a promising scintillator material; however, the crystal growth yield must be improved for it to become commercially viable. This study measures strain accumulations in the crystal lattice which can contribute to cracking during post-growth cooling. Neutron diffraction is used to measure the crystal structure of undoped and 5 mol% europium-doped BaBrCl from 303 to 1073 K, approaching the melting point. Rietveld analysis of these data provides the temperature dependence of the thermal and chemical strain in BaBrCl. In particular, anisotropic thermal expansion is measured, with expansion along the b axis nearly double the expansion along the a and c axes. Additionally, the chemical strain from the incorporation of europium atoms peaks around 673 K, explaining cracking frequently observed in that temperature range.

A non-destructive neutron analysis technique performed at the IMAT beamline of the STFC (Science and Technology Facility Council), UK, is presented. In this experiment, neutrons of different energy have been exploited to obtain a tomographic reconstruction of a biomineralic sample, more specifically a cultured pearl, by using a time-resolving pixel camera, the MicroChannel Plate (MCP) detector, utilizing an array of 2 × 2 Timepix readout chips. The MCP camera is capable of energy-resolved two-dimensional mapping of neutron transmission with a spatial resolution of ~ 55 μm. By using a Simultaneous Iterative Reconstruction Technique (SIRT), virtual sections of the internal part of the sample have been created, thus revealing several features inside its bulk. The crystallographic phase map via Bragg edge analysis, showing a phase fraction distribution on the entire specimen, has been generated as well. Finally, 3D volume rendering of the pearl is presented.

Microstructures produced by Additive Manufacturing (AM) techniques determine many characteristics of components produced by this particular manufacturing technique. Residual stress and texture are among those characteristics, which need to be optimized to meet dimensional and strength requirements. Post-build heat treatments are necessary to relief residual stresses, homogenize the microstructure and to develop the necessary microstructures (precipitation or solution hardening) for strength. Our focus in this study is the measurement of residual stresses during a vacuum stress relief (VSR) heat treatment. We employ the energy-resolved neutron imaging to investigate, in-situ, the uniformity of the as-built texture and to map the residual strain distributions within samples of Inconel 625 (IN625). The samples used in this study were printed using the powder-bed metal laser melting additive manufacturing technique. Strain and texture variations were measured at room temperature for the as-built samples as well as their changes during stress relief annealing at 700 °C and 875 °C in a vacuum furnace. The uniformity of crystalline plane distribution, from which texture can be inferred, was imaged with sub-mm spatial resolution for the entire sample area exceeding several square centimeters. Despite the limited accuracy of in-situ lattice strain reconstruction during sample annealing, the results indicate that most of the strain relaxation occurs at 700 °C within the first 2–3 h. Relaxation of the strain at 875 °C happened at a much faster rate. In addition, energy-resolved neutron imaging demonstrates the possibility to correlate the uniformity of grain orientation and the degree of texture variations with printing parameters, in particular the laser translation speed. Simulations of the AM build process were carried out to predict the residual stress distributions within the samples as a function of the build process parameters. Comparisons of the simulation results to the room temperature experimental measurements show good agreements when the simulation data are averaged over the volume of the part confirming the usefulness of the experiments for validating simulation results. The neutron imaging technique described in this study can be helpful for the evaluation of bulk crystallographic characteristics in AM printed materials and can be used as a guide for developing the heat treatment cycle and for validations of VSR simulation results.

The investigation of microstructure of crystalline materials is one of the possible and frequently used applications of energy-resolved neutron imaging. The position of Bragg edges is defined by sharp changes in neutron transmission and can thus be determined by the measurement of the transmission spectra as a function of neutron wavelength. The accuracy of this measurement depends on both the data analysis technique and the quality of the measured spectra. While the optimization of reconstruction methods was addressed in several previous studies, here we introduce an important prerequisite when aiming for high resolution Bragg edge strain imaging — a well calibrated flight path across the entire field of view (FOV). Compared to e.g. powder diffraction, imaging often uses slightly different geometries and hence requires a calibration for each particular setup. We herein show the importance of this calibration across the entire FOV in order to determine the instrumental error correction for pulsed neutron beamlines. In addition, we also consider the precision of Bragg edge reconstruction as a function of integration time and the minimal sample area. We demonstrate that, with a proper calibration procedure, the Bragg edge wavelength distribution across the entire sample can be reconstructed with an accuracy of Δ λ ∕ λ = ± ∼ 0.01%. Our experiments indicate that the strain maps of Inconel 625 samples printed by a direct metal laser melting additive manufacturing technique can be reconstructed with the precision of ± ∼ 100 μ e . The full FOV calibration technique becomes even more important with the development of advanced neutron energy-resolved imaging beamlines and detectors with large FOVs.

The uncertainties and the stability of a neutron sensitive MCP/Timepix detector when operating in the event timing mode for quantitative image analysis at a pulsed neutron source were investigated. The dominant component to the uncertainty arises from the counting statistics. The contribution of the overlap correction to the uncertainty was concluded to be negligible from considerations based on the error propagation even if a pixel occupation probability is more than 50%. We, additionally, have taken into account the multiple counting effect in consideration of the counting statistics. Furthermore, the detection efficiency of this detector system changes under relatively high neutron fluxes due to the ageing effects of current Microchannel Plates. Since this efficiency change is position-dependent, it induces a memory image. The memory effect can be significantly reduced with correction procedures using the rate equations describing the permanent gain degradation and the scrubbing effect on the inner surfaces of the MCP pores.

This paper presents a proof-of-concept demonstration of triaxial strain tomography from Bragg-edge neutron imaging within a three-dimensional sample. Bragg-edge neutron transmission can provide high-resolution images of the average through thickness strain within a polycrystalline material. This poses an associated rich tomography problem which seeks to reconstruct the full triaxial strain field from these images. The presented demonstration is an important step towards solving this problem, and towards a technique capable of studying the residual strain and stress within engineering components. A Gaussian process based approach is used that ensures the reconstruction satisfies equilibrium and known boundary conditions. This approach is demonstrated experimentally on a non-trivial steel sample with use of the RADEN instrument at the Japan Proton Accelerator Research Complex. Validation of the reconstruction is provided by comparison with conventional strain scans from the KOWARI constant-wavelength strain diffractometer at the Australian Nuclear Science and Technology Organisation and simulations via finite element analysis.

Energy-resolved neutron imaging experiments conducted on the Small Angle Neutron Scattering (SANS) instrument, Bilby, demonstrate how the capabilities of this instrument can be enhanced by a relatively simple addition of a compact neutron counting detector. Together with possible SANS sample surveying and location of the region of interest, this instrument is attractive for many imaging applications. In particular, the combination of the cold spectrum of the neutron beam and its pulsed nature enables unique non-destructive studies of the internal structure for samples that are opaque to other more traditional techniques. In addition to conventional white beam neutron radiography, we conducted energy-resolved imaging experiments capable of resolving features related to microstructure in crystalline materials with a spatial resolution down to ∼0.1 mm. The optimized settings for the beamline configuration were determined for the imaging modality, where the compromise between the beam intensity and the achievable spatial resolution is of key concern.

Combined three-dimensional (3D) mapping of (micro-)structures with elemental and crystalline phase variations is of significant importance for the characterization of materials. Neutron wavelength selective imaging is a spectral imaging technique that exploits unique contrast differences e.g. for mapping dissimilar elemental, isotope, or phase compositions, and has the particular advantage of being applicable to sample volumes on the meso- and macroscale. While being mostly applied as radiography (2D) so far, we herein report that the extension to tomography allows for the display of the full spectral information for every voxel and in 3D. The development is supported by example data from a continuous as well as a pulsed neutron source. As a practical example, we collected 4D data sets (3D + spectral) of plastically deformed metastable stainless steel and herein demonstrate an improved quantification strategy for crystalline phase fractions. These exemplary results illustrate that localized phase transformations can be quantified even in complex geometries within centimeter-sized samples, and we will discuss the limits and future prospects of the technique that is not limited to crystalline materials.

There is renewed interest in using advanced techniques to characterize ancient Roman concrete due to its exceptional durability and low-carbon footprint. In the present work, samples were drilled from the “Hospitium” in Pompeii and were analyzed by synchrotron microtomography (μCT) and neutron radiography to study how the microstructure, including the presence of induced cracks, affects their water adsorption. The water distribution and absorptivity were quantified by neutron radiography. The 3D crack propagation, pore size distribution and orientation, tortuosity, and connectivity were analyzed from μCT results using advanced imaging methods. Porosity was also measured by mercury intrusion porosimetry (MIP) as a reference. Ductile fracture patterns were observed once cracks were introduced. Compared to Portland cement mortar/concrete, the Pompeii samples had relatively high porosity, low connectivity, and a similar coefficient of capillary penetration. In addition, permeability was predicted from models based on percolation theory and pore structure data to evaluate the fluid transport properties. Understanding the microstructure of ancient Pompeii concrete is important because it could inspire the development of modern concrete with high durability.

An approach for tomographic reconstruction of three-dimensional strain distributions from Bragg-edge neutron transmission strain images is outlined and investigated. This algorithm is based on the link between Bragg-edge strain measurements and the Longitudinal Ray Transform, which has been shown to be sensitive only to boundary displacement. By exploiting this observation we provide a method for reconstructing boundary displacement from sets of Bragg-edge strain images. In the case where these displacements are strictly the result of externally applied tractions, corresponding internal strain fields can then be found through traditional linear-static finite element methods. This approach is tested on synthetic data in two-dimensions, where the rate of convergence in the presence of measurement noise and beam attenuation is examined.

Energy-resolved neutron transmission imaging is utilised for in situ comparisons of strain distributions in fastened assemblies with regular and self-locking Spiralock® female threads. The strain maps measured within torqued steel bolts indicate that for a Spiralock® thread, the load is distributed over a larger section of the fastener, making this type of thread more suitable for fastening of assemblies subject to transverse vibrations.

Energy-resolved neutron imaging is used for a nondestructive study of bulk internal microstructure, elemental composition and distribution of voids in dissimilar metal-alloy welds of ∼10 mm thickness. All these characteristics are measured simultaneously in one experiment with a few hundred micrometre spatial resolution., A nondestructive study of the internal structure and compositional gradient of dissimilar metal-alloy welds through energy-resolved neutron imaging is described in this paper. The ability of neutrons to penetrate thick metal objects (up to several cm) provides a unique possibility to examine samples which are opaque to other conventional techniques. The presence of Bragg edges in the measured neutron transmission spectra can be used to characterize the internal residual strain within the samples and some microstructural features, e.g. texture within the grains, while neutron resonance absorption provides the possibility to map the degree of uniformity in mixing of the participating alloys and intermetallic formation within the welds. In addition, voids and other defects can be revealed by the variation of neutron attenuation across the samples. This paper demonstrates the potential of neutron energy-resolved imaging to measure all these characteristics simultaneously in a single experiment with sub-mm spatial resolution. Two dissimilar alloy welds are used in this study: Al autogenously laser welded to steel, and Ti gas metal arc welded (GMAW) to stainless steel using Cu as a filler alloy. The cold metal transfer variant of the GMAW process was used in joining the Ti to the stainless steel in order to minimize the heat input. The distributions of the lattice parameter and texture variation in these welds as well as the presence of voids and defects in the melt region are mapped across the welds. The depth of the thermal front in the Al–steel weld is clearly resolved and could be used to optimize the welding process. A highly textured structure is revealed in the Ti to stainless steel joint where copper was used as a filler wire. The limited diffusion of Ti into the weld region is also verified by the resonance absorption.

The unique possibilities enabled by neutron imaging for in situ remote diagnostics of microstructural characteristics during crystal growth are demonstrated, even when the materials and surrounding structures are opaque to other more conventional interrogation techniques. Neutron radiography is implemented to image remotely the uniformity of elemental distribution (e.g. dopant concentration) during crystal growth, the location of the liquid/solid interface and the presence of macroscopic crystal defects (e.g. cracks), all with a temporal resolution of 5–7 s., Neutrons are known to be unique probes in situations where other types of radiation fail to penetrate samples and their surrounding structures. In this paper it is demonstrated how thermal and cold neutron radiography can provide time-resolved imaging of materials while they are being processed (e.g. while growing single crystals). The processing equipment, in this case furnaces, and the scintillator materials are opaque to conventional X-ray interrogation techniques. The distribution of the europium activator within a BaBrCl:Eu scintillator (0.1 and 0.5% nominal doping concentrations per mole) is studied in situ during the melting and solidification processes with a temporal resolution of 5–7 s. The strong tendency of the Eu dopant to segregate during the solidification process is observed in repeated cycles, with Eu forming clusters on multiple length scales (only for clusters larger than ∼50 µm, as limited by the resolution of the present experiments). It is also demonstrated that the dopant concentration can be quantified even for very low concentration levels (∼0.1%) in 10 mm thick samples. The interface between the solid and liquid phases can also be imaged, provided there is a sufficient change in concentration of one of the elements with a sufficient neutron attenuation cross section. Tomographic imaging of the BaBrCl:0.1%Eu sample reveals a strong correlation between crystal fractures and Eu-deficient clusters. The results of these experiments demonstrate the unique capabilities of neutron imaging for in situ diagnostics and the optimization of crystal-growth procedures.

Computational models are employed to analyze residual chemical stresses arising from compositional variations in europium-doped BaBrCl crystals grown by the vertical Bridgman method. We find that significant chemical stress is produced by radial segregation of Eu in this system. In particular, the distribution of normal stresses is set by the radial concentration gradient, whose changing sign produces surface states in tension or compression. Crack opening from surface flaws will be promoted or suppressed by tensile or compressive surface stresses, respectively. Thus, crystal growth processing strategies that change the radial dopant concentration gradients are posited to affect the propensity for cracking. For this system, surface stresses are changed from states of tension to compression when the growth rate is increased, thus improving the chances to avoid cracking—a strategy that defies classical wisdom that dictates slower growth to improve outcomes. Similar strategies affecting segregation may prove beneficial to tailor chemical stress fields to reduce cracking in other crystal growth systems.