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SUMMARY The influence of the cathode flow field properties on the water distribution and performance of direct methanol fuel cells (DMFCs) was studied. All measurements were performed with DMFC stack cells ( A = 314.75 cm2). The local and temporal water distributions in the flow field channels during DMFC operation were visualized by means of through-plane neutron radiography. Current and temperature distributions were measured simultaneously by the segmented cell technology. Additionally, the time-dependent current distribution, cell performance and pressure drop were measured. Cathode flow field designs with channel and grid structures were compared. The cathode flow field channels were impregnated by either hydrophobizing or hydrophilizing agents or used as received. It turned out that hydrophobized and partially also untreated flow fields cause large water droplets in the cathode channels. The water droplets cause a blocking of the air flow and consequently a lower and more unstable (fluctuating) performance, less steady current and temperature distributions, and higher pressure drops between cathode inlet and outlet. Because of their two-dimensional design, grid flow fields are less prone to water accumulations. The best results are achieved with a hydrophilized grid flow field that has a channel depth and width of 1.5 mm each ('C-GR15'). Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Photosynthetic efficacy and auto-exhaust-fume resistance of street trees were evaluated by cold neutron radiography (CNR) with D2O tracer and chlorophyll fluorescence (CF) imaging. With these techniques, information on the responses of water usage and photosynthetic activity of plants exposed to simulate toxic auto-exhaust fumes (2ppm SO2 in air) were obtained. Branches of hibiscus trees were detached, placed into a tub with aerated water and used for the experiments after rooting. A CF image was taken before SO2 was applied for 1h. During the experiment, CNR and CF imaging were conduced. H2O and D2O in the plant container were exchanged every 30min to observe water uptake. D2O tracer clearly showed water uptake into the hibiscus stem during each treatment. When the atmosphere was changed from simulated auto-exhaust fumes to normal air again, the amount of D2O and, hence, water uptake increased. CF imaging was well suited to evaluate the effects of SO2 as simulated toxic auto-exhaust fumes on plants. The maximum photochemical efficiency (F v/F m), a sensitive indicator of the efficacy and the integrity of plants’ photosynthesis, immediately dropped by 30% after supplying the simulated auto-exhaust fumes. This indicates that toxic auto-exhaust fumes negatively affected the photosynthetic activity of hibiscus leaves. Simultaneous CNR and CF imaging successfully visualized variations of photosynthetic activity and water uptake in the sample. Thus, this combination method was effective to non-destructive analyze the physiological status of plants. [Copyright &y& Elsevier]

Zn–MnO2 alkaline batteries were investigated in situ at different stages of electric discharge by synchrotron tomography with monochromatic x rays and by neutron tomography. The spatial distribution and the changes in the morphology of different components of a battery caused by the reduction of MnO2, the dissolution of Zn, and the nucleation and growth of ZnO are investigated with high spatial resolution around several micrometers with x rays. Neutron tomography is used to monitor the changes in the spatial distribution of hydrogen in the MnO2 matrix and provides complementary information about the process. [ABSTRACT FROM AUTHOR]

Abstract: The new cold neutron radiography instrument CONRAD is a multifunctional facility for radiography and tomography with cold neutrons at Hahn–Meitner Institut, Berlin. It is located at the end of a curved neutron guide, which faces the cold-neutron source of the BER-II research reactor. The geometry provides a cold-neutron beam with wavelengths between 2 and 12Å. Two measuring positions are available for radiography and tomography investigations. The first one is placed at the end of the guide and it is optimized for in situ experiments in which a high neutron flux is required. The available flux at this position is approximately 108 cm−2 s−1. The second measuring position uses a pin-hole geometry which allows better beam collimation (L/D up to 1000) and higher image resolution in the range of 200μm in the CCD based detector system (10×10cm2). The use of cold neutrons for radiography purposes increases the image contrast and improves the sensibility e.g., the detection of small amounts of water and hydrogen-containing materials in metal matrixes. On the other hand the cold-neutron beam can be modified easily by using diffraction and neutron optical techniques. This enables to perform radiography and tomography experiments with more sophisticated measuring techniques. Recent examples of research and industrial applications will be presented. [Copyright &y& Elsevier]

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 Å/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. [ABSTRACT FROM AUTHOR]

This work describes the implementation of polarized neutron imaging capabilities at the neutron and x-ray tomograph (NeXT) imaging station of the Institut Laue Langevin. This development enhances the capacity of this instrument to study advanced magnetic materials, which are crucial in a variety of engineering applications. Here, the feasibility of polarized neutron imaging at NeXT is demonstrated by visualizing the magnetic field generated by a simple bar magnet. The use of a double-crystal monochromator for wavelength-resolved imaging is also shown to enable both quantitative and qualitative analyses of magnetic materials. This is demonstrated through the determination of magnetization strength in a sample of electric steel (FeSi) in addition to the distribution of its components. Polarimetric imaging is also implemented for the first time to characterize the magnetic field generated by a current-carrying cylindrical wire. These findings collectively underscore the value of incorporating polarized neutron imaging into the already cutting-edge imaging station. [ABSTRACT FROM AUTHOR]

Knowing the distribution of a magnetic field in bulk materials is important for understanding basic phenomena and developing functional magnetic materials. Microscopic imaging techniques employing X-rays, light, electrons, or scanning probe methods have been used to quantify magnetic fields within planar thin magnetic films in 2D or magnetic vector fields within comparable thin volumes in 3D. Some years ago, neutron imaging has been demonstrated to be a unique tool to detect magnetic fields and magnetic domain structures within bulk materials. Here, we show how arbitrary magnetic vector fields within bulk materials can be visualized and quantified in 3D using a set of nine spin-polarized neutron imaging measurements and a novel tensorial multiplicative algebraic reconstruction technique (TMART). We first verify the method by measuring the known magnetic field of an electric coil and then investigate the unknown trapped magnetic flux within the type-I superconductor lead. Mapping the distribution of magnetic fields inside bulk materials is challenging but crucial to understand and develop functional magnetic materials. Here the authors demonstrate the capability to visualize 3D vector magnetic fields inside materials using spin-polarized neutron tomography and tensorial reconstruction techniques. [ABSTRACT FROM AUTHOR]

In this study, we report the first case of non-destructive characterization of the dependence of the flux trapping mechanism on the grain properties of a bulk type II superconductor using a combination of polarized neutron tomography and diffraction contrast tomography. The high temperature superconductor, YBa 2 Cu 3 O 7 −δ , has been used in this study due to its viable commercial growth processes typically resulting in the production of polycrystalline specimens. The diffraction tomography revealed the pseudo-single crystal nature of the sample i.e. a polycrystalline sample with 47 composite grains having a maximum grain misorientation angle of 1.86°. Polarized neutron tomography was used for characterization of the flux trapped in the material after field cooling to 90.5 K in a field of 0.5 mT and switching off the field. A combination of the results from these two non-destructive characterization techniques indicate a correlation between the anisotropy of the trapped flux with the orientation of the grains in the material in addition to a preference for the flux trapping in the grain boundaries. • Non-destructive field & grain characterization in YBCO via neutron tomography • Grain reconstruction reveals pseudo-single crystal nature of sample. • Trapped field direction correlate with grain orientation. • Field trapping correlate with grain boundaries. [ABSTRACT FROM AUTHOR]

Abstract: 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 3He detector with a spatial resolution of 2×3mm2 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. [Copyright &y& Elsevier]

Patterns of vertebral variation across mammals have seldom been quantified, making it difficult to test hypotheses of covariation within the axial skeleton and mechanisms behind the high level of vertebral conservatism among mammals. We examined variation in vertebral counts within 42 species of mammals, representing monotremes, marsupials and major clades of placentals. These data show that xenarthrans and afrotherians have, on average, a high proportion of individuals with meristic deviations from species' median series counts. Monotremes, xenarthrans, afrotherians and primates show relatively high variation in thoracolumbar vertebral count. Among the clades sampled in our dataset, rodents are the least variable, with several species not showing any deviations from median vertebral counts, or vertebral anomalies such as asymmetric ribs or transitional vertebrae. Most mammals show significant correlations between sacral position and length of the rib cage; only a few show a correlation between sacral position and number of sternebrae. The former result is consistent with the hypothesis that adult axial skeletal structures patterned by distinct mesodermal tissues are modular and covary; the latter is not. Variable levels of correlation among these structures may indicate that the boundaries of prim/abaxial mesodermal precursors of the axial skeleton are not uniform across species. We do not find evidence for a higher frequency of vertebral anomalies in our sample of embryos or neonates than in post-natal individuals of any species, contrary to the hypothesis that stabilizing selection plays a major role in vertebral patterning. [ABSTRACT FROM AUTHOR]

Abstract: Water flow imaging may help to better understand various problems related to water stress of plants. It may help to fully understand the water relations of plants. The objective of this research was to estimate the velocity of water flow in plant samples. Cut roses (Rosa hybrida, var. ‘Milva’) were used as samples. Cold neutron radiography (CNR) was conducted at CONRAD, Helmholtz Center Berlin for Materials and Energy, Berlin, Germany. D2O and H2O were interchangeably injected into the water feeding system of the sample. After the uptake of D2O, the neutron transmission increased due to the smaller attenuation coefficient of D2O compared to H2O. Replacement of D2O in the rose peduncle was clearly observed. Three different optical flow algorithms, Block Matching, Horn–Schunck and Lucas–Kanade, were used to calculate the vector of D2O tracer flow. The quality of sequential images providing sufficient spatial and temporal resolution allowed to estimate flow vector. [Copyright &y& Elsevier]

Abstract: Differential phase contrast imaging resolves angular deviations of a beam due to phase shifts induced by a sample and thereby enables the visualisation and three-dimensional reconstruction of the refractive index distribution of a sample additional to the attenuation coefficient addressed by conventional radiography and tomography. Two instrumental techniques, namely double crystal diffractometers and a grating interferometer setup, are suitable to detect this kind of contrast. According to the high angular resolution of these methods they are suited to additionally detect dark field contrast, i.e. (ultra) small angle scattering contrast. Magnetic fields add to the refractive index for neutrons and consequently magnetic structures can in principle also be imaged by these methods. Relations between the methods will be discussed and an overview of current developments will be given. [Copyright &y& Elsevier]

Abstract: Improving the spatial resolution conditions in a neutron imaging experiment enables the detection of phase-based contrast in addition to attenuation contrast. Addressing not only the amplitude but also the phase of radiation in an imaging experiment allows for obtaining additional information about the sample. The so-called neutron phase contrast method improves imaging results mainly by edge enhancement which increases the visibility of sub-resolution structures and of low attenuation contrast materials. These effects have been found at high intensity synchrotron X-ray sources before and have been applied to neutron imaging recently. However, the excellent coherence conditions and spatial resolution of imaging instruments at state-of-the-art synchrotron sources can hardly be compared to neutron imaging. Nevertheless, edge enhancement has been found for increased resolution (coherence) conditions in neutron experiments as well. As for X-ray instruments the effects have been explained by diffraction, although typical interference fringes have never been recorded. In contrast this article will explain the effects measured with neutron radiation by refraction and total reflection. Both of these do not require high spatial coherence. Therefore improved resolution and not increased coherence will be considered as precondition to obtain the reported signals and to understand the results. Considerations concerning relaxed collimation requirements for improved detector resolutions will be presented as a consequence. [Copyright &y& Elsevier]

Abstract: It has been shown in earlier works that smallest beam deviations (μrad) caused by refraction can be used to reconstruct the macroscopic inner structure of samples by the means of tomography. Hence, structures of low contrast materials, i.e. materials with low values or differences of attenuation coefficients, could be imaged by tomographic reconstruction although the conventional attenuation contrast method failed. Such tomographic scans have mainly been performed in a bent crystal-type double crystal diffractometer (DCD) using a one-dimensional position sensitive detector (PSD). This setup provided only q-resolution in the PSD, while the spatial resolution was achieved by scanning the sample through a slit collimated beam. The first practical application of this method shall be introduced here and advantages compared to the conventional method will be discussed. The measurement of two samples, a test with a dummy sample and a measurement of a sample requested by a company, are the examples to be reported. [Copyright &y& Elsevier]

Abstract: Absorption is just one of a number of imaging signals used in neutron tomography. Within the last years, phase contrast, refraction and ultra small-angle scattering as imaging signals have been investigated as well as real-time radiography or energy-dispersive absorption. The use of cold neutrons () implies for many neutron tomograms a better absorption contrast, larger refraction angles, larger small-angle scattering angles and better phase contrast. The reconstruction procedures for refraction and ultra small-angle scattering tomographies are different from other signals, however, they can be transformed to data sets and then be reconstructed with well-known programs. Examples will be given of all these techniques. [Copyright &y& Elsevier]

Polarized neutron imaging has many applications through characterization of magnetic fields generated from currents or magnetic moments. If local magnetic field directions change slowly relative to its precession frequency, the angle between neutron polarization vector and the local field vector remains constant. Conversely, if the fields change rapidly relative to the precession frequency, this angle may vary. The transition between these scenarios follows the adiabatic condition. In this study, we analyze the effects of the adiabatic condition on a polarized neutron image. Two case studies are used for illustrating possible scenarios. The first case shows how an external field, due to the adiabatic condition, influences the symmetry of a polarized neutron image of a current carrying solenoid. The second case study shows how the adiabatic coupling of the beam polarization could lead to the loss of contrast in a polarized neutron image while studying field penetration in type II superconductors. Both case studies serve to highlight the importance of taking this phenomenon into account while interpreting polarized neutron imaging data given the rising importance of the technique as a characterization method in magnetism and superconductivity research. [ABSTRACT FROM AUTHOR]

[Display omitted] • Design and Implementation of Polarized Neutron Imaging for the first time on IMAT imaging station at ISIS Neutron and Muon Source. • Validation of the system via characterization of the homogeneous magnetic field produced from a solenoid. • Magnetic characterization of additively manufactured MnAl samples indicate their magnetic anisotropy can be engineered via optimization of scan parameters. In this study, we report the first case of design and implementation of a polarized neutron imaging option on the Imaging and Materials Science & Engineering Station (IMAT). This is a significant addition to the capabilities of the station that allows the characterization of advanced magnetic materials for different engineering applications. Combining its time-of-flight feature with a polarized beam yields data that facilitate both quantitative and qualitative analysis of magnetic materials. Using the simple field of an aluminium solenoid, we perform a characterization of the new setup. In addition, we present polarized measurements of additively manufactured (AM) MnAl samples where the magnetic anisotropy due to the fabrication process has been investigated as a first scientific application of the setup. The results indicate that the anisotropy of the material can be engineered through variation of the AM fabrication parameters. [ABSTRACT FROM AUTHOR]

Abstract: Spin-echo modulation small-angle neutron scattering (SEMSANS) is based on the detection of spatial beam modulation, which is induced by triangular spin echo precession regions and subsequent spin analyses. In order to detect such signal and exploit it for small angle scattering investigations neutron detection with sub-millimeter spatial resolution is required. Here an approach is reported where instead of a position sensitive detector an absorption grating is used to analyze the beam modulation stepwise. The spin-echo length scan in this case is performed by varying the sample-to-detector distance. The real space correlation functions of reference sample structures in the range 102 nm, i.e. giving rise to small-angle scattering in the very small-angle range, are recorded and analyzed successfully. [Copyright &y& Elsevier]

Abstract: We report an investigation of the phase transitions between water and ice using neutron imaging as a research tool. Because of the high scattering cross section of hydrogen for slow neutrons, very small amounts of water can easily be quantified by this technique. However, it is not easy to determine the aggregate state (liquid or solid) if the sample does not have a well defined size, as might happen in the case of water produced in PEM fuel cells. It is important to be able to judge the state of the water (or ice), particularly when it is not easily accessible or hidden by the surrounding structure. The neutron interaction properties of the two aggregates (water and ice) were investigated in dynamic series, in which light water and heavy water were frozen under controlled conditions; transmission images were taken continuously during the phase transition. In addition to the expected density reduction of the ice, some other features were also observed in the images, causing the derived neutron transmission data to differ from the tabulated nuclear data. Energy-selective experiments with thermally stabilized water (+10°C) and ice (−10°C) showed different interaction behaviors for the two aggregates in the neutron wavelength range of 2–6Å. We found clear differences in the absolute values of the attenuation cross-sections and the slopes of their energy dependencies. This result might be used in the future as a criterion to distinguish between the aggregate states in arbitrary water or ice assemblies. [Copyright &y& Elsevier]

The aim of this study is to characterize the microstructure and high temperature induced structural changes within fiber reinforced silicon carbide (SiC/SiC) composites by means of non-destructive techniques. In order to understand their properties, the characterization of the microstructure of SiC/SiC composites is the crucial issue. Porosity within composites is unavoidable with currently available manufacturing processes, and reduces significantly the life time and performance of the composites under harsh environments. Moreover, the internal pores, created in the manufacturing process cause the degradation most of the outstanding properties such as thermal conductivity, mechanical properties at high temperature, and radiation stability. Cold neutron tomography and diffusion structural diagnostic techniques were applied in the investigation of the microstructure of SiC/SiC composites to gain complementary information. One of the main obstacles to using these composites in fusion technology and other applications are a change of the porous structure and a swelling at high temperatures and in a severe radiation environment. Cold neutron tomography enables visualization of the microstructure of the composite and consequently the pore distributions within the SiC/SiC composite were observed with a suitable resolution. The diffusion structural diagnostic technique was used to characterize the thermal behavior of SiC/SiC composites on heating up to 1300 °C. [ABSTRACT FROM AUTHOR]