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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.

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.

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.

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

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 MCP-based neutron counting detector is a novel device that allows high spatial resolution and time-resolved neutron radiography and tomography with epithermal, thermal and cold neutrons. Time resolution is possible by the high readout speeds of ~ 1200 frames/sec, allowing high resolution event counting with relatively high rates without spatial resolution degradation due to event overlaps. The electronic readout is based on a Timepix sensor, a CMOS pixel readout chip developed at CERN. Currently, a geometry of a quad Timepix detector is used with an active format of 28 × 28 mm2 limited by the size of the Timepix quad (2 × 2 chips) readout. Measurements of a set of high-precision micrometers test samples have been performed at the Imaging and Materials Science & Engineering (IMAT) beamline operating at the ISIS spallation neutron source (U.K.). The aim of these experiments was the full characterization of the chip misalignment and of the gaps between each pad in the quad Timepix sensor. Such misalignment causes distortions of the recorded shape of the sample analyzed. We present in this work a post-processing image procedure that considers and corrects these effects. Results of the correction will be discussed and the efficacy of this method evaluated.

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.

Bragg-edge strain imaging from energy-resolved neutron transmission measurements poses an interesting tomography problem. The solution to this problem will allow the reconstruction of detailed triaxial stress and strain distributions within polycrystalline solids from sets of Bragg-edge strain images. Work over the last decade has provided some solutions for a limited number of special cases. In this paper, we provide a general approach to reconstruction of an arbitrary system based on a least squares process constrained by equilibrium. This approach is developed in two- dimensions before being demonstrated experimentally on two samples using the RADEN instrument at the J-PARC spallation neutron source in Japan. Validation of the resulting reconstructions is provided through a comparison to conventional constant wavelength strain measurements carried out on the KOWARI engineering diffractometer within ANSTO in Australia. The paper concludes with a discussion on the range of problems to be addressed in a three-dimensional implementation.

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.

We apply continuum models to analyze phase change, heat transfer, fluid flow, solute transport, and segregation in order to understand prior neutron imaging observations of the vertical gradient freeze growth of Eu-doped BaBrCl. The models provide a rigorous framework in which to understand the mechanisms that are responsible for the complicated evolution of interface shape and dopant distribution in the growth experiment. We explain how a transition in the solid/liquid interface shape from concave to convex is driven by changes in radial heat transfer caused by furnace design. We also provide a mechanistic explanation of how dynamic growth conditions and changes of the flow structure in the melt result in complicated segregation patterns in this system. A growth pause caused by controller lock-up is shown to result in a band of solute depletion in accordance with classical theory. However, changing flow patterns during growth result in a non-monotonic axial distribution of solute that cannot be explained by simple application of classical segregation models. We assert that the approach presented here, namely the use of rigorous models in conjunction advanced diagnostics, such as neutron imaging, provides an exciting path forward for process optimization and control, accelerating the incremental advances that have, in the past, typically relied on empiricism, experience, and intuition.

The development of highly pixelated fast Medipix/Timepix readout enabled a large number of novel hybrid detectors, where incoming particles/photons are initially converted into a measureable charge, typically exceeding 1000 electrons. Among those possible converters are Microchannel plate (MCP) electron multipliers, which provide some unique capabilities when combined with bare Medipix/Timepix readout. Fast event multiplication with ~10–20 ps time jitter, localized within the MCP pore (typically 5–10 μm in diameter) and low dark currents make MCP/Medipix/Timepix hybrid devices very attractive for the high spatial and temporal resolution detection of low energy photons (soft X-ray, UV and visible), alpha particles, ions and also neutrons. In this review we present a brief overview of the capabilities of MCP/Medipix/Timepix detectors and show the results of experiments conducted with such hybrid detectors in various applications including neutron imaging, astronomy, mass spectroscopy and others.

In this study we compare conventional X-ray imaging with neutron radiography and neutron tomography of several crowned teeth and teeth with amalgam fillings. While X-ray images provide detailed information about the root area, they cannot probe anything in the area where metals are present, e.g. underneath the crown or behind the metal filling. Our results demonstrate that neutron radiography and neutron tomographic imaging can reveal the internal structure of treated teeth underneath the crown. These neutron imaging methods can be used to investigate the interaction of various fillings and crown attachment paste with the crown and the tooth itself. The integrity of tooth and fillings underneath the crown, the location of cavities and voids can be visualized in three dimensions and provide means for the improvements of dental filling and crown attachment materials and methods.

Energy-resolved neutron transmission imaging is used to reconstruct maps of residual strains in drilled and cold-expanded holes in 5-mm and 6.4-mm-thick aluminum plates. The possibility of measuring the positions of Bragg edges in the transmission spectrum in each 55 × 55 µm2 pixel is utilized in the reconstruction of the strain distribution within the entire imaged area of the sample, all from a single measurement. Although the reconstructed strain is averaged through the sample thickness, this technique reveals strain asymmetries within the sample and thus provides information complementary to other well-established non-destructive testing methods.

Many high resolution event counting devices process one event at a time and cannot register simultaneous events. In this article a frame-based readout event counting detector consisting of a pair of Microchannel Plates and a quad Timepix readout is described. More than 10 4 simultaneous events can be detected with a spatial resolution of ~55 µm, while >103 simultaneous events can be detected with 1200 frames/sec, while the global count rate of the detector can exceed 5×108 particles/s when no timing information on every particle is required. For the first generation Timepix readout, the timing resolution is limited by the Timepix clock to 10–20 ns. Optimization of the MCP gain, rear field voltage and Timepix threshold levels are crucial for the device performance and that is the main subject of this article. These devices can be very attractive for applications where the photon/electron/ion/neutron counting with high spatial and temporal resolution is required, such as energy resolved neutron imaging, Time of Flight experiments in lidar applications, experiments on photoelectron spectroscopy and many others.

Planar solid oxide electrochemical cells (SOC) are composed of at least three layers: a anode, a electrolyte and a cathode [1]. Cermet Ni-YSZ (yttria stabilized zirconia) is a material widely used for production of anodes in solid oxide fuel cells (SOFC) and cathodes in solid oxide electrolysis cells (SOEC), but also for supports. Mechanical and electrochemical performance of these layers, and thus whole cells, depends on their microstructure. One of the commonly used deposition techniques of the Ni-YSZ supports is tape-casting from a NiO-YSZ slurry, followed by sintering and reduction of NiO during the initial operation of the cell. Conditions, i.e. temperature, atmosphere and stress, applied during this procedure, determine the microstructure of the support and thereby the cell performance, therefore in-situ observation of these processes under different conditions can provide knowledge needed to optimize the SOC performance. Neutron imaging [2] is a nondestructive measurement method holding a great potential for in-situ characterization of SOC. In contrast to X-ray imaging, due to high material penetration by neutrons, it is possible not only to image real size SOC stacks, but also to perform experiments in-situ, using sample environment providing the SOC operation conditions. Here we present the results of energy resolved neutron imaging measurements applied to in-situ investigations of Ni-YSZ anode supports for SOFCs. The energy resolved neutron imaging technique is based on the measurement of neutron transmission through the sample depending on neutron energy/wavelength. In the achieved patterns, sudden changes in transmission/ attenuation – so called “Bragg edges”- occur at certain neutron wavelengths, which correspond to d-spacing values present in the investigated polycrystalline material. Thus, such Bragg edge patterns (fig.1a) contain information about elements, crystal structure, crystalline phases in a sample, texture or strain field. Bragg edge patterns can be measured both at continuous and pulsed neutron sources. In the first case, where a polychromatic continuous neutron beam is generated, Bragg edge patterns are obtained by selecting specific neutron wavelengths using monochromators and subsequent measurements of transmission for different wavelengths. In the second case, where pulses of white neutron radiation are created, neutrons with different wavelength (and velocity) reach the sample at different times. Using detectors able to record simultaneously intensity of the transmitted beam and corresponding neutron arrival time, whole Bragg edge patterns are acquired at once. This approach is called time of flight (TOF) method. We present the results of in-situ investigation of NiO reduction and re-oxidation in anode supports performed by means of energy resolved neutron imaging at both continuous (SINQ, PSI ,fig.1b) and pulsed neutron source ( ISIS, fig.1a). Figure 1a presents Bragg edge patterns recorded at ISIS around an edge corresponding to the d-spacing of NiO(200). Different patterns were measured at different times during the reduction. It is apparent, how the height of the NiO edge decreases with time. As the edge height depends on the amount of the NiO phase, it is possible to compare the reaction rate in different regions of the sample by evaluating the Bragg edge patterns for these regions. In our previous work [3] we have demonstrated by ex-situ Bragg edge neutron imaging feasibility to detect and distinguish Ni and NiO phases within the Ni-YSZ composite. Figure 1b shows the Ni and NiO phase distribution in Ni-YSZ bars after consecutive reduction and re-oxidation processes performed at a continuous neutron source. In-situ neutron imaging was performed using our custom built furnace [4]. Its design allows to meet the requirements of the equipment used at neutron imaging instruments, to achieve the required spatial resolution of images, and at the same time, to provide conditions required for conducting NiO reduction i.e. high temperature and reactive atmosphere. Since in a real SOFC, anode supports are always exposed to high thermal and mechanical stresses, progress of NiO-YSZ reduction should be investigated in samples under applied stress [5]. Therefore, our furnace is equipped with a loading system for applying stress to the sample during the reduction process. In this work, we present results of in-situ observation of the phase transition during the NiO-YSZ reduction and re-oxidation performed under different conditions: different temperatures, with and without applied stress. [1] S. Singhal, Solid State Ionics, vol. 135, no. 1–4, pp. 305–313, Nov. 2000. [2] M. Strobl et al., J. Phys.D.Appl.Phys., vol. 42, no. 24, p. 243001, Dec. 2009. [3] M. G. Makowska et al.; J. Appl. Cryst. 48, doi:10.1107/S1600576715002794, 2015. [4] M. G. Makowska et al.; submitted to RSI , 2015. [5] H. L. Frandsen et al., Conf. Proc. Eur. Fuel Cell Forum, Lucerne, Switz., 2014. Figure 1

The cold neutron spectrum of the Beamline for neutron Optics and other Applications (BOA) at Paul Scherrer Institut enables high contrast neutron imaging because neutron cross sections for many materials increase with neutron wavelength. However, for many neutron imaging applications, spatial resolution can be as important as contrast. In this paper the neutron transmission imaging capabilities of an MCP/Timepix detector installed at the BOA beamline are presented, demonstrating the possibilities for studying sub-20 µm features in various samples. In addition to conventional neutron radiography and microtomography, the high degree of neutron polarization at the BOA beamline can be very attractive for imaging of magnetic fields, as demonstrated by our measurements. We also show that a collimated cold neutron beamline combined with a high resolution detector can produce image artifacts, (e.g. edge enhancements) due to neutron refraction and scattering. The results of our experiments indicate that the BOA beamline is a valuable addition to neutron imaging facilities, providing improved and sometimes unique capabilities for non-destructive studies with cold neutrons.

The unique capabilities of neutrons to penetrate materials opaque to X-rays and at the same time to interact with hydrogen make neutron radiography a technique of choice for the quantification of hydrogen-containing substances. However, the interaction of neutrons with hydrogen is through scattering, not absorption and unwanted scattered neutrons can be responsible for a considerable fraction of the registered events, reducing the accuracy of hydrogen quantification, especially in imaging experiments where the sample has to be placed close to the detector to avoid image blurring due to the finite beam divergence. Various post-experiment data processing techniques were developed to correct and mitigate the effects of scattering. Another complementary 'hardware' solution described in this paper, is to simply eliminate the detrimental scattering component from the detected signal through the use of neutron collimators. Development of compact polycapillary collimators, merely a few mm thick, now enables accurate, high spatial resolution quantification of a wide range of materials which tend to strongly scatter neutrons. This paper demonstrates how it is now possible to substantially improve the accuracy of the measured water content in cement samples. A compact polycapillary neutron collimator (2 mm thick, 5 cm diameter, with ∼8 µm pores hexagonally packed on ∼10 µm centers) used for scatter rejection in our experiments. The water content within the 1×1×2 cm3 cement samples is measured by neutron transmission radiography, performed with sub-100 µm spatial resolution. The measurement of water concentration is markedly improved through the use of this collimator, proving those can be attractive for the experiments where samples must be placed in quite close proximity (e.g., only few centimeters or closer), from the neutron detector active surface.

Recently, two new phenomena linking stress field and reduction rates in anode-supported solid oxide fuel cells (SOFCs) have been demonstrated, so-called accelerated creep during reduction and reduction rate enhancement and nucleation due to stress (Frandsenet al., 2014). These complex phenomena are difficult to study and it is demonstrated here that energy-resolved neutron imaging is a feasible technique for combined mechanics–chemical composition studies of SOFC components, including commercially produced ones. Cermet anode supports, which prior to the measurements were reduced under varying conditions such as different temperatures, various times and different values of applied stress, have been measured. Thus, samples with different contents (and gradients) of Ni and NiO phases were investigated. The first Bragg edge transmission neutron measurements applied for the studies of the reduction progress in these samples were performed at two neutron beamline facilities (ISIS in the UK, Helmholtz Zentrum Berlin in Germany). The obtained results demonstrate the possibility to image and distinguish NiO and Ni phases within SOFC anode supports by energy-resolved neutron imaging and the potential of the neutron imaging method forin situstudies of reduction processes.

A cold neutron imaging and diffraction instrument, IMAT, is currently being constructed at the ISIS second target station. IMAT will capitalize on time-of-flight transmission and diffraction techniques available at a pulsed neutron source. Analytical techniques will include neutron radiography, neutron tomography, energy-selective neutron imaging, and spatially resolved diffraction scans for residual strain and texture determination. Commissioning of the instrument will start in 2015, with time-resolving imaging detectors and two diffraction detector prototype modules. IMAT will be operated as a user facility for material science applications and will be open for developments of time-of-flight imaging methods.

A new neutron imaging and diffraction facility, called IMAT, is currently being commissioned at the ISIS pulsed neutron spallation source. IMAT will take advantage of neutron time-of-flight measurement techniques for flexible neutron energy selection and effective energy discrimination. The instrument will be completed and commissioned within the next few months, after neutrons have been recently delivered to the sample area. From 2016 IMAT will enable white-beam neutron radiography and tomography as well as energy-dependent neutron imaging. The facility will offer a spatial resolution down to 50 microns for a field of view of up to 400 cm(2). IMAT will be operated as a user facility for material science applications and will be open for developments of time-of-flight imaging methods.

The cold neutron imaging and diffraction instrument IMAT at the second target station of the pulsed neutron source ISIS is currently being commissioned and prepared for user operation. IMAT will enable white-beam neutron radiography and tomography. One of the benefits of operating on a pulsed source is to determine the neutron energy via a time of flight measurement, thus enabling energy-selective and energy-dispersive neutron imaging, for maximizing image contrasts between given materials and for mapping structure and microstructure properties. We survey the hardware and software components for data collection and image analysis on IMAT, and provide a step-by-step procedure for operating the instrument for energy-dispersive imaging using a two-phase metal test object as an example.

IMAT is a new cold-neutron imaging facility at the neutron spallation source ISIS at the Rutherford Appleton Laboratory, U.K.. The ISIS pulsed source enables energy-selective and energy-resolved neutron imaging via time-of-flight (TOF) techniques, which are available in addition to the white-beam neutron radiography and tomography options. A spatial resolution of about 50 μm for white-beam neutron radiography was achieved early in the IMAT commissioning phase. In this work we have made the first steps towards achieving higher spatial resolution. A white-beam radiography with 18 μm spatial resolution was achieved in this experiment. This result was possible by using the event counting neutron pixel detector based on micro-channel plates (MCP) coupled with a Timepix readout chip with 55 μm sized pixels, and by employing an event centroiding technique. The prospects for energy-selective neutron radiography for this centroiding mode are discussed.

Energy-resolved neutron imaging is investigated as a real-time diagnostic tool for visualization and in-situ measurements of “blind” processes. This technique is demonstrated for the Bridgman-type crystal growth enabling remote and direct measurements of growth parameters crucial for process optimization. The location and shape of the interface between liquid and solid phases are monitored in real-time, concurrently with the measurement of elemental distribution within the growth volume and with the identification of structural features with a ~100 μm spatial resolution. Such diagnostics can substantially reduce the development time between exploratory small scale growth of new materials and their subsequent commercial production. This technique is widely applicable and is not limited to crystal growth processes.

Pulsed neutron transmission imaging is a unique method that can give spatially dependent information on physical values of materials, such as crystallographic characteristics, elements, magnetic field, and so on. These data are obtained by analyzing the transmission spectra dependent on the neutron wavelength observed at each pixel of a 2-D position sensitive detector. We applied this method to cultural heritage samples. As test samples, we have studied Japanese swords. Three of them are fragments of swords with different areas and ages and the fourth is a full size one. We found that there were differences in texture and crystallite size among fragment samples, and the quenched area was clearly demonstrated in the full size sword. Furthermore, a Chinese coin was studied, and major elements and differences in crystallographic characteristics in the coin were indicated. The results indicated that the pulsed neutron transmission method can nondestructively give information that cannot be easily obtained by other methods., Restaurierung und Archäologie, Bd. 8 (2015): Restaurierung und Archäologie

Spin Echo Modulated Small Angle Neutron Scattering with spatial resolution, i.e. quantitative Spin Echo Dark Field Imaging, is an emerging technique coupling neutron imaging with spatially resolved quantitative small angle scattering information. However, the currently achieved relatively large modulation periods of the order of millimeters are superimposed to the images of the samples. So far this required an independent reduction and analyses of the image and scattering information encoded in the measured data and is involving extensive curve fitting routines. Apart from requiring a priori decisions potentially limiting the information content that is extractable also a straightforward judgment of the data quality and information content is hindered. In contrast we propose a significantly simplified routine directly applied to the measured data, which does not only allow an immediate first assessment of data quality and delaying decisions on potentially information content limiting further reduction steps to a later and better informed state, but also, as results suggest, generally better analyses. In addition the method enables to drop the spatial resolution detector requirement for non spatially resolved Spin Echo Modulated Small Angle Neutron Scattering

The capability to produce a bright, short neutron pulse at the McClellan Nuclear Research Center (MNRC) can be very attractive for some neutron imaging applications. Complementary to conventional thermal neutron radiography conducted at the reactor, operating at the average power of 1 MW, a short pulse of ~25 ms FWHM duration can be produced at MNRC with the peak power exceeding 350 MW. Combination of a fast thermal neutron counting detector with a short neutron pulse at MNRC, enables high-resolution stroboscopic imaging to complement conventional neutron radiography. The results presented in this paper demonstrate the MNRC capabilities for conducting conventional thermal neutron radiography, demonstrating imaging spatial resolution below 100 μm, as well as bright flash neutron radiography with multiple nearly simultaneous events detected with microsecond timing resolution.

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

Neutron radiography is one of the non-destructive testing techniques which can provide characterization complimentary to X-rays and in many cases unique information on the samples. The relatively h...

The Japan Spallation Neutron Source (JSNS) at the Japan Proton Accelerator Research Complex (J-PARC) was developed as a 1- MW spallation neutron source. A Ag-In-Cd alloy was used as the decoupler material in two decoupled moderators. Although the Ag-In-Cd decoupler brings about superior neutronic performance, it has the disadvantage of high residual radioactivity. A Au-In- Cd alloy has been proposed as a solution to this problem. Recently, we successfully produced a ternary Au-In-Cd alloy. The alloy composition was 74.9 at% Au, 0.5 at% In, and 24.6 at% Cd. The distribution of the elements in the alloy was first determined by energy-dispersive X-ray (EDX) analysis. However, it was difficult to measure the In distribution by EDX because the amount of In is very small, and its spectrum is similar to that of Cd. Therefore, pulsed neutron imaging using both a time gated camera system and a multi-channel plate detector was performed to measure the elements in the Au-In-Cd alloy. The analysis was performed at the BL10 in the JSNS on samples of the Au-In-Cd alloy, an In foil, and two Au foils. With this technique, the distribution of Au, In, and Cd in the Au-In-Cd specimen was distinctly determined.

The goal of the Advanced Non-destructive Fuel Examination (ANDE) work package is the development and application of non-destructive neutron imaging and scattering techniques to ceramic and metallic nuclear fuels, ultimately also to irradiated fuels. The results of these characterizations provide complete pre- and post-irradiation on length scales ranging from mm to nm, guide destructive examination, and inform modelling efforts. Besides technique development and application to samples to be irradiated, the ANDE work package also examines possible technologies to provide these characterization techniques pool-side, e.g. at the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) using laser-driven intense pulsed neutron and gamma sources. Neutron tomography and neutron diffraction characterizations were performed on nine pellets; four UN/ U-Si composite formulations (two enrichment levels), three pure U3Si5 reference formulations (two enrichment levels), and two reject pellets with visible flaws (to qualify the technique). The 235U enrichments ranged from 0.2 to 8.8 wt. %. The nitride/silicide composites are candidate compositions for use as Accident Tolerant Fuel (ATF). The monophase U3Si5 material was included as a reference. Pellets from the same fabrication batches will be inserted in the Advanced Test Reactor at Idaho during 2016. We have also proposed a data format to buildmore » a database for characterization results of individual pellets. Neutron data reported in this report were collected in the LANSCE run cycle that started in September 2015 and ended in March 2016. This report provides the results for the characterized samples and discussion in the context of ANDE and APIE. We quantified the gamma spectra of several samples in their received state as well as after neutron irradiation to ensure that the neutron irradiation does not add significant activation that would complicate shipment and handling. We demonstrated synchrotron-based 3D X-ray microscopy on the composite fuel materials, providing unparalleled level of detail on the 3D microstructure. Furthermore, we initiated development of shielding containers allowing the characterizations presented herein while allowing handling of irradiated samples.« less

Energy-resolved neutron imaging enables non-destructive analyses of bulk structure and elemental composition, which can be resolved with high spatial resolution at bright pulsed spallation neutron sources due to recent developments and improvements of neutron counting detectors. This technique, suitable for many applications, is demonstrated here with a specific study of ~5–10 mm thick natural gold samples. Through the analysis of neutron absorption resonances the spatial distribution of palladium (with average elemental concentration of ~0.4 atom% and ~5 atom%) is mapped within the gold samples. At the same time, the analysis of coherent neutron scattering in the thermal and cold energy regimes reveals which samples have a single-crystalline bulk structure through the entire sample volume. A spatially resolved analysis is possible because neutron transmission spectra are measured simultaneously on each detector pixel in the epithermal, thermal and cold energy ranges. With a pixel size of 55 μm and a detector-area of 512 by 512 pixels, a total of 262,144 neutron transmission spectra are measured concurrently. The results of our experiments indicate that high resolution energy-resolved neutron imaging is a very attractive analytical technique in cases where other conventional non-destructive methods are ineffective due to sample opacity.

Tomographic imaging and diffraction measurements were performed on nine pellets; four UN/ U Si composite formulations (two enrichment levels), three pure U3Si5 reference formulations (two enrichment levels) and two reject pellets with visible flaws (to qualify the technique). The U-235 enrichments ranged from 0.2 to 8.8 wt.%. The nitride/silicide composites are candidate compositions for use as Accident Tolerant Fuel (ATF). The monophase U3Si5 material was included as a reference. Pellets from the same fabrication batches will be inserted in the Advanced Test Reactor at Idaho during 2016. The goal of the Advanced Non-destructive Fuel Examination work package is the development and application of non-destructive neutron imaging and scattering techniques to ceramic and metallic nuclear fuels. Data reported in this report were collected in the LANSCE run cycle that started in September 2015 and ended in March 2016. Data analysis is ongoing; thus, this report provides a preliminary review of the measurements and provides an overview of the characterized samples.

This article reports on in situ macroscopic scale imaging of NiO-YSZ (YSZ is yttria-stabilized zirconia) reduction under applied stress - a phase transition taking place in solid oxide electrochemical cells in a reducing atmosphere of a hydrogen/nitrogen mixture and at operation temperatures of up to 1073K. This process is critical for the performance and lifetime of the cells. Energy-resolved neutron imaging was applied to observe the phase transition directly with time and spatial resolution. Two different approaches are presented for using this imaging technique for the investigation of chemical and physical processes requiring controlled atmosphere and elevated temperature. The first type of measurement is based on alternating stages of short-term partial chemical reaction and longer neutron image acquisition, and the second type is a real in situ neutron imaging experiment. Results of applying energy-resolved neutron imaging with both approaches to the NiO-YSZ reduction investigation indicate enhancement of the reduction rate due to applied stress, which is consistent with the results of the authors' previous research.Results of the first in situ energy-resolved neutron imaging of NiO-YSZ (YSZ is yttria-stabilized zirconia) reduction under applied stress are presented. Neutron experiments were performed at the pulsed neutron source ISIS (UK) using a time-of-flight approach.

The event counting detection technology based on signal amplification in microchannel plates (MCPs) was initially developed for the applications with relatively low fluxes of photons, electrons and...