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A systematic study has been carried out to investigate the neutron transmission signal as a function of sample temperature. In particular, the experimentally determined wavelength-dependent neutron attenuation spectra for a martensitic steel at temperatures ranging from 21 to 700°C are compared with simulated data. A theoretical description that includes the Debye–Waller factor in order to describe the temperature influence on the neutron cross sections was implemented in the nxsPlotter software and used for the simulations. The analysis of the attenuation coefficients at varying temperatures shows that the missing contributions due to elastic and inelastic scattering can be clearly distinguished: while the elastically scattered intensities decrease with higher temperatures, the inelastically scattered intensities increase, and the two can be separated from each other by analysing unique sharp features in the form of Bragg edges. This study presents the first systematic approach to quantify this effect and can serve as a basis , for example, to correct measurements taken during in situ heat treatments, in many cases being a prerequisite for obtaining quantifiable results.

Nakhlite meteorites are igneous rocks from Mars that were aqueously altered ~630 million years ago. Hydrothermal systems on Earth are known to provide microhabitats; knowledge of the extent and duration of these systems is crucial to establish whether they could sustain life elsewhere in the Solar System. Here, we explore the three-dimensional distribution of hydrous phases within the Miller Range 03346 nakhlite meteorite using nondestructive neutron and x-ray tomography to determine whether alteration is interconnected and pervasive. The results reveal discrete clusters of hydrous phases within and surrounding olivine grains, with limited interconnectivity between clusters. This implies that the fluid was localized and originated from the melting of local subsurface ice following an impact event. Consequently, the duration of the hydrous alteration was likely short, meaning that the martian crust sampled by the nakhlites could not have provided habitable environments that could harbor any life on Mars during the Amazonian.

While laser powder-bed fusion has overcome some of the design constraints of conventional manufacturing meth-ods, it requires careful selection of process parameters and scan strategies to obtain favorable properties. Here we show that even simple scan strategies, complex ones being inevitable when printing intricate designs, can inadvertently produce local alterations of the microstructure and preferential grain orientation over small areas - which easily remain unnoticed across the macroscale. We describe how a combined usage of neutron imaging and electron backscatter diffraction can reveal these localized variations and explain their origin within cm-sized parts. We explain the observed contrast variations by linking the neutron images to simulated data, pole figures and EBSD, providing an invaluable reference for future studies and showing that presumably minor changes of the scan strategy can have detrimental effects on the mechanical properties. In-situ tensile tests reveal that fracture occurs in a region that was re-melted during the building process.

Hydrogen interaction with metals is well known to have severe detrimental effects on their mechanical properties. The use of modern high-strength steels, which are attractive to improve fuel economy by reducing weight as well as candidates for H storage cylinders and other components, is currently being severely limited by the fact that the presence of H can cause embrittlement of the material. In addition to steel, several other metals and alloys used in the nuclear industry, like Ti and Zr, are susceptible to H degradation through hydride formation and subsequent cracking. Microstructure-specific H mapping has been recognized as the most important challenge on the pathway towards a better understanding of the nature of H embrittlement in metallic alloys [1,2] as well as the development of H storage solutions based on metal hydrides [3]. Unfortunately, the characterization of H interactions with metals is an extremely challenging task and neutron-based techniques are of exceptional importance in this matter because - contrary to X-rays and electrons - thermal and cold neutrons interact strongly with the H nuclei [4], while the neutron beam is only weakly attenuated by the relevant metallic materials. Therefore, hydrogen distributions can be measured and quantified even in 3D by tomographic methods [5]. Here we present several neutron imaging investigations of embrittlement and cracking in Fe and Zr based metal alloys and optimization studies of hydrogen storage systems containing metal hydrides as an active substance. The advantages and the limitations of the experimental methods as well as the attempts for hydrogen quantification will be discussed in detail.

The boron-10 based Multi-Grid detector is being developed as an alternative to helium-3 based neutron detectors. At the European Spallation Source, the detector will be used for time-of-flight neutron spectroscopy at cold to thermal neutron energies. The objective of this work is to investigate fine time- and energy-resolved effects of the Multi-Grid detector, down to a few $\mu$eV, while comparing it to the performance of a typical helium-3 tube. Furthermore, it is to characterize differences between the detector technologies in terms of internal scattering, as well as the time reconstruction of ~ $\mu$s short neutron pulses. The data were taken at the Helmholtz Zentrum Berlin, where the Multi-Grid detector and a helium-3 tube were installed at the ESS test beamline, V20. Using a Fermi-chopper, the neutron beam of the reactor was chopped into a few tens of $\mu$s wide pulses before reaching the detector, located a few tens of cm downstream. The data of the measurements show an agreement between the derived and calculated neutron detection efficiency curve. The data also provide fine details on the effect of internal scattering, and how it can be reduced. For the first time, the chopper resolution was comparable to the timing resolution of the Multi-Grid detector. This allowed a detailed study of time- and energy resolved effects, as well as a comparison with a typical helium-3 tube., Comment: 37 pages, 21 figures

Ferromagnetic shape-memory CoNiGa alloys have attracted much scientific interest due to their potential alternative use as high-temperature shape-memory alloys, bearing a high prospect for actuation and damping applications at elevated temperatures. Yet, polycrystalline CoNiGa, due to strong orientation dependence of transformation strains, suffers from intergranular fracture. Here, two multi-grain CoNiGa samples were prepared by a novel hot extrusion process that can promote favourable grain-boundary orientation distribution and improve the material's mechanical behaviour. The samples were investigated by multiple methods and their micro structural, magnetic, and mechanical properties are reported. It is found that a post-extrusion solutionising heat treatment leads to the formation of a two-phase oligocrystalline homogeneous microstructure consisting of an austenitic parent B2 phase and gamma-CoNiGa precipitates. Reconstruction of the full 3D grain morphology revealed large, nearly spherical grains with no low-angle grain boundaries throughout the entire sample volume. The presence of gamma precipitation affects the transformation behaviour of the samples, by lowering the martensitic transformation temperature, while, in conjunction with the oligocrystalline microstructure, it improves the ductility. Controlling the composition of the B2 matrix, as well as the phase fraction of the gamma phase, is thus crucial for the optimal behaviour of the alloys. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

A prototype quasi-parasitic thermal neutron beam monitor based on isotropic neutron scattering from a thin natural vanadium foil and standard $^3$He proportional counters is conceptualized, designed, simulated, calibrated, and commissioned. The European Spallation Source designed to deliver the highest integrated neutron flux originating from a pulsed source is currently under construction in Lund, Sweden. The effort to investigate a vanadium-based neutron beam monitor was triggered by a list of requirements for Beam Monitors permanently placed in the ESS neutron beams in order to provide reliable monitoring at complex beamlines: low attenuation, linear response over a wide range of neutron fluxes, near to constant efficiency for neutron wavelengths in a range of 0.6-10 \r{A}, calibration stability and the possibility to place the system in vacuum are all desirable characteristics. The scattering-based prototype, employing a natural vanadium foil and standard $^3$He proportional counters, was investigated at the V17 and V20 neutron beamlines of the Helmholtz-Zentrum in Berlin, Germany, in several different geometrical configurations of the $^3$He proportional counters around the foil. Response linearity is successfully demonstrated for foil thicknesses ranging from 0.04 mm to 3.15 mm. Attenuation lower than 1% for thermal neutrons is demonstrated for the 0.04 mm and 0.125 mm foils. The geometries used for the experiment were simulated allowing for absolute flux calibration and establishing the possible range of efficiencies for various designs of the prototype. The operational flux limits for the beam monitor prototype were established as a dependency of the background radiation and prototype geometry. The herein demonstrated prototype monitors can be employed for neutron fluxes ranging from $10^3-10^{10}$ n/s/cm$^2$.

Texture in materials is important as it contributes to anisotropy in the bulk mechanical properties. Ti-6Al-4V built with the additive manufacturing process (AM) electron beam melting (EBM) has been found to have anisotropic mechanical properties. Therefore, this work has been performed to investigate the texture variations of EBM built Ti-6Al-4V with neutron time of flight (TOF). For the work, samples were produced with different build geometries off-set by 90 degrees. A cast sample was additionally analyzed to investigate the bulk texture of conventionally manufactured material. Microstructural characterization was performed and the cast material was found to have a coarse colony α microstructure, whereas the EBM built material had a finer basket weave microstructure. Overall, the texture of the EBM built material was found to be weak having an multiple of random distribution (MRD) index of ~1 for the α phase, whilst the cast material possessed more than twice the amount of preferred orientation i.e. MRD 2.51 for the α phase.

Variation of texture in Ti-6Al-4V samples produced by three different additive manufacturing (AM) processes has been studied by neutron time-of-flight (TOF) diffraction. The investigated AM processes were electron beam melting (EBM), selective laser melting (SLM) and laser metal wire deposition (LMwD). Additionally, for the LMwD material separate measurements were done on samples from the top and bottom pieces in order to detect potential texture variations between areas close to and distant from the supporting substrate in the manufacturing process. Electron backscattered diffraction (EBSD) was also performed on material parallel and perpendicular to the build direction to characterize the microstructure. Understanding the context of texture for AM processes is of significant relevance as texture can be linked to anisotropic mechanical behavior. It was found that LMwD had the strongest texture while the two powder bed fusion (PBF) processes EBM and SLM displayed comparatively weaker texture. The texture of EBM and SLM was of the same order of magnitude. These results correlate well with previous microstructural studies. Additionally, texture variations were found in the LMwD sample, where the part closest to the substrate featured stronger texture than the corresponding top part. The crystal direction of the α phase with the strongest texture component was [ 11 2 ¯ 3 ] .

Imaging techniques based on neutron beams are rapidly developing and have become versatile non-destructive analyzing tools in many research fields. Due to their intrinsic properties, neutrons differ strongly from electrons, protons or X-rays in terms of their interaction with matter: they penetrate deeply into most common metallic materials while they have a high sensitivity to light elements such as hydrogen, hydrogenous substances, or lithium. This makes neutrons perfectly suited probes for research on materials that are used for energy storage and conversion, e.g., batteries, hydrogen storage, fuel cells, etc. Moreover, their wave properties can be exploited to perform diffraction, phase-contrast and dark-field imaging experiments. Their magnetic moment allows for resolving magnetic properties in bulk samples. This review will focus on recent applications of neutron imaging techniques in both materials research and fundamental science illustrated by examples selected from different areas.

Neutron imaging is a highly successful experimental technique ever since adequate neutron sources were available. In general, neutron imaging is performed with a wide wavelength spectrum for best flux conditions in transmission geometry. Neutrons provide outstanding features in the penetration of many structural materials, which often makes them more suited for bulk sample studies than other forms of radiation, often in particular as they are also highly sensitive to some light elements, especially Hydrogen. In contrast to neutron scattering applications, imaging resolves macroscopic structures, nowadays down to, in the best case, below 10 micrometre, directly in real space. However, since more than a decade there is a growing number of techniques and applications in neutron imaging that – supported by powerful neutron sources – are taking advantage of wavelength resolved measurements. In this review we summarize and discuss this outstanding development and how wavelength resolved transmission neutron imaging is successfully exploiting diffraction mechanisms to access crystal structure information in the Angstrom regime, which conventionally is probed in reciprocal space by diffraction techniques. In particular the combination of information gained in real space and on crystallographic length scales makes this neutron imaging technique a valuable tool for a wide range of new applications, while it also qualifies neutron imaging to fully profit from the new generation of powerful pulsed neutron sources. Fil: Woracek, Robin. European Spallation Source ERIC; Suecia Fil: Santisteban, Javier Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Fedrigo, Anna. European Spallation Source ERIC; Suecia. Paul-Scherrer Institute; Suiza. Universidad de Copenhagen; Dinamarca Fil: Strobl, Markus. European Spallation Source ERIC; Suecia

Carbon fiber-reinforced vinyl ester composite facings are being considered by the US Navy for sandwich structures with either low-density polyvinyl chloride foam or balsa wood as the core materials manufactured using Vacuum-Assisted Resin Transfer Molding process. In this paper, experimental techniques are developed to evaluate the variation of surface strain spatially using three-dimensional Digital Image Correlation technique and internal damage evolution using radiation-based tomography. Both X-ray and neutron radiation was utilized to evaluate the microstructure of composite laminate facings in three dimensions at high resolution. Since naval structures are exposed to harsh sea environment, samples were soaked in simulated sea water at 40℃ for long duration, well beyond saturation stage of Fickian diffusion ascertained using weight gain measurements. Results for a series of mechanical tests on fiber dominated samples of [0/90]2S and matrix dominated samples of [±45]2S orientation are reported. Variable specimen sizes (12.5 mm wide by 100 mm long, 25 mm by 200 mm, and 25 mm by 300 mm, all with an average uniform thickness of 2.8 mm) for laboratory tests are utilized in order to evaluate the applicability of results for large ship structures. Different carbon fiber-reinforced vinyl ester failure mechanisms of matrix crack interactions, such as matrix dominated transverse tension, tension along fibers, and fiber delamination were observed. Digital Image Correlation technique was useful to track the existence of localized damage for both fiber and matrix dominated carbon fiber-reinforced vinyl ester laminates. High resolution X-ray and neutron tomography under in-situ mechanical loading were used to investigate interior microstructure evolution and damage at chosen stress levels. The new techniques presented in this paper can enable a comparison between interior specimen damage and surface damage (readily observable using Digital Image Correlation). Use of different modality of radiation (neutrons versus X-rays) was very useful to probe damage resulting from moisture diffused in the matrix resin and fiber interface/interphase and shows a lot of promise for studying the failure modes and damage evolution in polymeric composites and sandwich structures.

In this paper, the degradation of mechanical properties of marine structural aluminum alloy AA5083 and onset of lattice plastic anisotropy subsequent to fire exposure is investigated. For virgin and fire-exposed samples, microstructural characterization is carried out for the first time and changes in lattice specific strain responses under step and continuous axial deformation are studied using novel bulk neutron diffraction. Peak fitting of raw data yields d-spacing values of reflections of interest and allows for lattice specific strain calculations. A reduction in yield stress from 260 MPa in the virgin material to 120 MPa in the fire-exposed sample is observed. Virgin material exhibits dynamic strain aging during plastic deformation; this is captured in neutron diffraction measurements. Larger peak broadening for virgin material indicates possible presence of Type II and III residual stresses due to intergranular stress or dislocation stress fields. Stress vs. lattice strain plots show large deviations from linearity post-yield for fire-exposed samples. This is due to strain redistribution among grains as well as grain reorientation. After fire exposure dynamic strain aging does not occur, but individual lattice planes reveal plastic anisotropy in their response to plastic deformation. Results from neutron diffraction, combined with electron backscatter diffraction characterization, provide insight into the yielding mechanisms of AA5083 and effects of fire exposure.

The European Spallation Source (ESS), scheduled to start operation in 2020, is aiming to deliver the most intense neutron beams for experimental research of any facility worldwide. Its long pulse time structure implies significant differences for instrumentation compared to other spallation sources which, in contrast, are all providing short neutron pulses. In order to enable the development of methods and technology adapted to this novel type of source well in advance of the first instruments being constructed at ESS, a test beamline (TBL) was designed and built at the BER II research reactor at Helmholtz-Zentrum Berlin (HZB). Operating the TBL shall provide valuable experience in order to allow for a smooth start of operations at ESS. The beamline is capable of mimicking the ESS pulse structure by a double chopper system and provides variable wavelength resolution as low as 0.5% over a wide wavelength band between 1.6 A and 10 A by a dedicated wavelength frame multiplication (WFM) chopper system. WFM is proposed for several ESS instruments to allow for flexible time-of-flight resolution. Hence, ESS will benefit from the TBL which offers unique possibilities for testing methods and components. This article describes the main capabilities of the instrument, its performance as experimentally verified during the commissioning, and its relevance to currently starting ESS instrumentation projects.

Neutron Bragg-edge imaging was applied for the visualization of a γ-austenite to α′-martensite phase transformation. In the present study, a super martensitic stainless steel sample was heated until complete austenitization and was subsequently cooled down to room temperature. The martensitic phase transformation started at M s = 190 °C. Using a monochromatic neutron beam with λ = 0.390 nm, the transmitted intensity was significantly reduced during cooling below M s, since the emerging martensitic phase has a higher attenuation coefficient than the austenitic phase at this wavelength. The phase transformation process was visualized by filming the transmission images from a scintillator screen with a CCD camera with a temporal resolution of 30 s and a spatial resolution of 100 µm.

The main objective of the European Spallation Source (ESS) is to perform consistently high impact neutron scattering science using the highest neutron flux of any facility in its class. This ambition is naturally accompanied by operational challenges related to the vertical integration of the instruments' hardware and software shared between collaborators from 13 European countries. The present work will detail integration tests performed at the V20 Test Instrument at Helmholtz-Zentrum Berlin in Germany. An ESS chopper prototype was successfully controlled through the ESS Chopper Integration Controller (CHIC) and Experimental Physics and Industrial Control System (EPICS). Neutron data were successfully collected and time stamped using neutron beam monitors, the ESS prototype detector readout electronics and the Data Management Software Center (DMSC) data acquisition (DAQ) software. Chopper rotation events were timestamped and the chopper disk showed excellent stability and neutron absorption characteristics. The test resulted in (i) the expected time-of-flight (TOF) response, (ii) collected data that compared well with instrument reference data and (iii) revealing the diagnostic power of the performed integration tests. The results of this integration test validate the ESS chopper and detector DAQ architecture choices., 8 pages, 9 figures

Residual stress/strain and microstructure used in additively manufactured material are strongly dependent on process parameter combination. With the aim to better understand and correlate process parameters used in electron beam melting (EBM) of Ti-6Al-4V with resulting phase distributions and residual stress/strains, extensive experimental work has been performed. A large number of polycrystalline Ti-6Al-4V specimens were produced with different optimized EBM process parameter combinations. These specimens were post-sequentially studied by using high-energy X-ray and neutron diffraction. In addition, visible light microscopy, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) studies were performed and linked to the other findings. Results show that the influence of scan speed and offset focus on resulting residual strain in a fully dense sample was not significant. In contrast to some previous literature, a uniform &alpha, and &beta, Ti phase distribution was found in all investigated specimens. Furthermore, no strong strain variations along the build direction with respect to the deposition were found. The magnitude of strain in &alpha, phase show some variations both in the build plane and along the build direction, which seemed to correlate with the size of the primary &beta, grains. However, no relation was found between measured residual strains in &alpha, phase. Large primary &beta, grains and texture appear to have a strong effect on X-ray based stress results with relatively small beam size, therefore it is suggested to use a large beam for representative bulk measurements and also to consider the prior &beta, grain size in experimental planning, as well as for mathematical modelling.

The European Spallation Source (ESS), which is under construction in Lund (Sweden), will be the next leading neutron facility with an unprecedented brilliance and novel long-pulse time structure. A long-pulse source not only provides a high time-average flux but also opens the possibility to tune the resolution by using pulse shaping choppers. Thus, an instrument can readily be operated in either a high flux or a high resolution mode. Several of the shorter instruments at the ESS will employ Wavelength Frame Multiplication (WFM) in order to enable a sufficient resolution while offering a continuous and broad wavelength range. A test beamline was operated until the end of 2019 at the research reactor in Berlin to test components and methods, including WFM, in order to prepare the new facility for the operation of neutron instruments and successful first science. We herein demonstrate the implementation of WFM for reflectometry. By selecting a short pulse mode under the same geometrical configuration, we compare and discuss the results for two reference samples. The reported experiments not only serve to prove the reliability of the WFM approach but also, for the first time, demonstrate the full instrument control, data acquisition and data reduction chain that will be implemented at the ESS.

The construction of the new neutron imaging instrument at the BER-2 research reactor of the Helmholtz-Zentrum Berlin has greatly increased the potential of the facility. The redesign of the facility included improvements of the neutron extraction and transportation systems, more effective shielding, and innovative instrumentation. The cold neutron flux at the neutron guide exit was increased by more than one order of magnitude, which allowed for an implementation of methods that require monochromatic or polarized beams, thus enabling the exploitation of nonconventional contrast mechanisms such as phase, diffraction and magnetic contrasts. The improved instrument design also facilitates the development of high-resolution neutron tomography by providing an increased beam intensity at the sample position.

Additive manufacturing is a promising and rapidly rising technology in metal processing. However, besides a number of key advantages the constitution of a part through a complex thermo-mechanical process implies also some severe issues with the potential of impacting the quality of products. In laser powder bed fusion (LPBF), the most applied metal additive manufacturing process, the repetitive heating and cooling cycles induce severe strains in the built material, which can have a number of adverse consequences such as deformation, cracking and decreased fatigue life that might lead to severe failure even already during processing. It has been reported recently that the application of laser shock peening (LSP) can counteract efficiently the named issues of LPBF through the introduction of beneficial compressive residual stresses in the surface regions mostly affected by tensile stresses from the manufacturing process. Here we demonstrate how lattice strains implied by LPBF and LSP can efficiently be characterized through diffraction contrast neutron imaging. Despite the spatial resolution need with regards to the significant gradients of the stress distribution and the specific microstructure, which prevent the application of more conventional methods, Bragg edge imaging succeeds to provide essential two-dimensionally spatial resolved strain maps in full field single exposure measurements.

An XYZ polarization analysis solution has been developed for the new thermal time-of-flight spectrometer TOPAS [1], to be operated in the coming east neutron guide hall at the MLZ. This prototype is currently being prepared to use on NEAT at HZB [2]. Polarization Analysis Studies on a Thermal Inelastic Spectrometer, commonly called PASTIS [3], is based on polarized 3He neutron spin filters and an XYZ field configuration for the sample environment and a polarization-preserving neutron guide field. The complete system was designed to provide adiabatic transport of the neutron polarization to the sample position on TOPAS while maintaining the homogeneity of the XYZ field. This complete system has now been tested on the polarized time-of-flight ESS test beam line V20 at HZB [4]. We present results of this test and the next steps forward.

Conventional neutron imaging utilizes the beam attenuation caused by scattering and absorption through the materials constituting an object in order to investigate its macroscopic inner structure. Small angle scattering has basically no impact on such images under the geometrical conditions applied. Nevertheless, in recent years different experimental methods have been developed in neutron imaging, which enable to not only generate contrast based on neutrons scattered to very small angles, but to map and quantify small angle scattering with the spatial resolution of neutron imaging. This enables neutron imaging to access length scales which are not directly resolved in real space and to investigate bulk structures and processes spanning multiple length scales from centimeters to tens of nanometers.

A simulation of realistic samples within a neutron scattering or imaging experiment has been created in order to support the accuracy, feasibility and analysis of residual stress measurements as well as the development of novel experimental methods and instrument components. Covering the influences of individual neutron instrument parameters, the simulation also assists in optimizing the experimental configuration towards precise measurements and effective usage of neutron beamtime.

Nondestructive 3D mapping of crystallographic phases is introduced providing distribution of phase fractions within the bulk (centimeter range) of samples with micrometer-scale resolution. The novel neutron tomography based technique overcomes critical limitations of existing techniques and offers a wide range of potential applications. It is demonstrated for steel samples exhibiting phase transformation after being subjected to tensile and torsional deformation.

The potential of wavelength resolved neutron transmission experiments is well known. This paper is focused on the performance of the double crystal monochromator which is widely used at steady state neutron sources and compares simulation results based on neutron ray tracing with experimental results in order to provide a better understanding of the device. The influences of crystal mosacities on the neutron beam is reported for the utilised setup and the resulting wavelength gradients along one direction are determined. For the neutron imaging geometry applied, a wavelength gradient of about 0.005 A/cm at the sample position was found. Moreover, a new neutron radiography technique for Bragg edge mapping in imaging experiments utilising a neutron wavelength gradient at the sample position was developed and is reported. Experiments and simulations are found to be in good agreement.

We report on measured neutron cross section data for super-cooled water and ice by time-of-flight neutron transmission imaging. In particular we demonstrate the use of high duty cycle time-of-flight (HDC-TOF) measurements to determine the local aggregate state of water with spatial resolution, by exploiting the neutron cross section dependence on the mobility of hydrogen atoms for long neutron wavelengths (> 4 Å). While one can envision many different applications for this method, one example is to provide insights into the freezing mechanism during the start-up of polymer electrolyte fuel cells from below zero degrees. Unlike for other wavelength selective measurements (e.g. Bragg edge imaging), only a limited wavelength resolution is required for this method. With a chopper setup with high duty cycle (30 %), we reached a high contrast-to-noise ratio (CNR) with a contrast between ice and super-cooled water of 8 %. To maximize the CNR, we optimized the duty cycle, pulse period and image processing parameters. Moreover, we present a theoretical framework for performing such optimization calculations, which can be used to maximize CNR for any beam line and any substances. For the optimization procedure presented in this publication, we used cross section values for ice and super-cooled water measured with high wavelength resolution using wavelength frame multiplication choppers. Our results show that the aggregate state of water of a sufficiently thick layer of water (> 0.5 mm) can be reliably determined for a small area (1 mm2 ) and with a reasonable short acquisition time of 5 minutes. Fil: Siegwart, Muriel Dorothea. Paul Scherrer Institut. Electrochemistry Laboratory; Suiza. Paul Scherrer Institut. Laboratory for Neutron Scattering and Imaging; Suiza Fil: Woracek, Robin. European Spallation Source ESS; Suecia Fil: Marquez Damian, Jose Ignacio. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Tremsin, Anton. University of California at Berkeley; Estados Unidos Fil: Manzi Orezzoli, Victoria. Paul Scherrer Institut. Electrochemistry Laboratory; Suiza Fil: Strobl, Markus. Paul Scherrer Institut. Laboratory for Neutron Scattering and Imaging; Suiza Fil: Schmidt, Treicy Johanna. Paul Scherrer Institut. Electrochemistry Laboratory; Suiza. Eidgenössische Technische Hochschule Zürich; Suiza. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Boillat, Pierre. Paul Scherrer Institut. Electrochemistry Laboratory; Suiza

We herein report on using a compact and low cost scintillator-camera based neutron detection system for quantitative time-of-flight imaging applications. While powerful pulsed neutron sources emerge and enable unprecedented scientific achievements, one bottleneck is the availability of suitable detectors that provide high count- and high frame- rate capabilities. For imaging applications the achievable spatial resolution/pixel size is obviously another key characteristic. While major effort was so far directed towards the development of neutron counting type imaging detectors, this work demonstrates that a camera based detector system as commonly employed at steady state sources can also be used if a suitable camera is utilized. This is demonstrated at the ESS test beamline (V20) at Helmholtz-Zentrum Berlin by recording the time-of-flight transmission spectrum of steel samples using a CMOS camera at 1 kHz frame rate, revealing the characteristic Bragg edge pattern. This 'simple' setup in the current state presents a useful option of neutron detection and has the potential to overcome many of the existing limitations and could provide a reliable alternative for neutron detector technology in general, given that the camera and scintillator technology keep up the current development speed.

Energy dependent neutron transmission imaging has recently gained attention for the potential to spatially resolve texture, crystallographic phase and lattice strain. Especially promising is the time-of-flight (TOF) approach that takes maximum advantage of the new generation of pulsed spallation neutron sources, such as SNS, JSNS and ESS. In this paper, the authors demonstrate the feasibility to efficiently apply the TOF approach at a continuous source in order to spatially resolve and quantify the (lattice) strain distribution in a flat steel sample under tensile loading. Although transmission-based TOF imaging for strain mapping at a pulsed source is well published, this work is the first attempt to demonstrate such measurement using choppers at a continuous neutron source. A critical component for spatially resolved TOF imaging is the availability of a high spatial resolution imaging detector, capable of the required time resolution. For the herein presented work, a conventional 2D position-sensitive 3 He detector with a spatial resolution of 2×3 mm 2 has been used for proof-of-principle measurements. The results are compared to conventional lattice strain measurements obtained at an engineering neutron diffractometer, where the same mechanical loading system was utilized. The efficiency of the time-of-flight transmission method is discussed with respect to other methods, at continuous as well as at pulsed sources.

Cold neutrons have a wavelength that is in the same range as the lattice spacings of most polycrystalline metallic materials. Imaging of such materials with monochromatic cold neutrons of different wavelengths provides a unique contrast due to coherent Bragg scattering. Additionally, the spectral positions of the Bragg edges can be mapped for each point of an image by using the transmission data of corresponding wavelength scans. We present investigations of welded components with such energy-selective neutron radiography around specific Bragg-edges in the transmission spectrum. Features in the local microstructure of the weld have been visualized.

Simultaneous use of neutron diffraction and attenuation based transmission Bragg edge imaging for strain measurements is demonstrated in this paper using the pulse neutron source at Los Alamos National Laboratory. Cylindrical samples made from ferritic steel have been subjected to in-situ elastic loading in tension and torsion. Lattice strains were investigated for both deformation modes by time-of-flight (TOF) neutron diffraction using two detector banks at 2θ of ±90°. At the same time, the transmitted portion of the neutron beam was recorded with the goal to analyze the position and shape of the Bragg edges, using a novel time/energy resolved Microchannel Plate (MCP) detector with pixel size of 55 µm and a 28x28 mm2 field of view. Lattice strains obtained using neutron diffraction indicate that the deformation path (tension versus torsion) has important effect on their evolution and related results are summarized.The emphasis of this paper is to explain the aspects of the experimental setup and data interpretation associated with neutron Bragg edge transmission technique for obtaining through-thickness averaged strain measurements. Implications of using transmission imaging based strain mapping for samples subjected to deformation under tensile loading (where stress at a given cross-section is constant) versus torsional loading (where stress varies linearly from center to outer radius) are discussed. In the case of samples subjected to tensile loading, analysis of the Bragg edge shifts provides the strain value in the direction of the transmitted beam. Thus, three strain components are measured simultaneously when performing Bragg edge imaging in addition to diffraction using two detector banks. For specimens subjected to pure shear by torsion, the Bragg edge transmission technique cannot readily provide quantitative strain information as the mid-point of the Bragg edge does not shift uniformly due to external loading, but results in a broadening of the Bragg edge. Such information can be used to describe the variation of strain distribution along the transmitted beam direction. Spatially resolved Bragg edge maps will be very helpful to detect d-spacing inhomogeneities within the illuminated volume, which may remain undetected when using diffraction only measurements.

Thermal neutron imaging is a powerful non-invasive diagnostic technique to study water management within a proton exchange membrane (PEM) fuel cell. To isolate the hydration behavior of membrane, significant increase in detecting thin water films is needed. A humidity cell is developed to study hydration of a PEM using cold neutron imaging. Spatial and temporal changes of PEM water uptake are quantified. Water film as small as 1 μm thick and corresponding to a volume containing 10 ng of liquid water at high spatial resolution is detected. This represents an order of magnitude improvement in water detection efficiency achievable at thermal neutron imaging facilities.

An experimental method, using in-situ neutron diffraction for the measurement of shear strain, based on (hkl) lattice spacing changes under torsional loading, is described. This method provides the ability to probe the response of crystallographic planes to application of shear stress, inside the bulk of samples that are subjected to torsion. To demonstrate the method, shear moduli corresponding to bcc (211), (200), and (110) were experimentally determined for a solid cylinder of ferritic alloy 12L14 under elastic loading. Results indicate that the elastic constants determined under torsional shear show a different degree of anisotropy than those obtained from tensile loading.

Wavelength selective neutron radiography at a cold neutron reactor source was used to measure strain and determine (residual) stresses in a steel sample under plane stress conditions. We present a new technique that uses an energy-resolved neutron imaging system based on a double crystal monochromator and is equipped with a specially developed (in situ) biaxial load frame to perform Bragg edge based transmission imaging. The neutron imaging technique provides a viewing area of 7 cm by 7 cm with a spatial resolution on the order of ∼ 100 μm. The stress-induced shifts of the Bragg edge corresponding to the (110) lattice plane were resolved spatially for a ferritic steel alloy A36 (ASTM international) sample. Furthermore it is demonstrated that results agree with comparative data obtained using neutron diffraction and resistance based strain-gauge rosettes.

This paper describes non-destructive three-dimensional (3D) mapping of crystallographic phase distributions within the bulk (centimeter range) of samples with micrometer-scale resolution. The technique leverages diffraction contrast due to Bragg scattering and the large penetration power of neutrons through high-atomic-number-element-based structural materials. Our tomographic approach overcomes critical limitations of existing techniques by allowing spatially resolved phase mapping in bulk samples and offers a wide range of potential applications. The technique is demonstrated for (metastable 304L stainless) steel samples that exhibit strain-induced martensitic phase transformation after being subjected to tensile and torsional deformation. The distribution of phase fractions within the 3D reconstructed volumes was verified at select locations using neutron diffraction as well as EBSD, and results agree with transformation kinetics theory.

The MIRACLES team., An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact of the early years of the ESS, and provide a solid base for completion and further expansion of the facility., Some of the work described here is part of projects that have received funding from the European Union’s Horizon 2020 research programme: SINE 2020 under grant agreement number 654000, BrightnESS under grant agreement number 676548, and SoNDe under grant agreement number 654124. Financial support for the fast-shutter upgrade for FREIA from Swedish Research Council VR, grant no 2018-05013, is acknowledged. The VESPA team gratefully acknowledges the Science & Technology Facilities Council (STFC) and the CNR , within the CNR-STFC Agreement (2014–2020) No. 3420.