High Resolution Neutron Imaging Research Articles

Unlocking high spatial resolution in neutron imaging through an add-on fibre optics taper.

The demand for high resolution neutron imaging has been steadily increasing over the past years. The number of facilities offering cutting edge resolution is however limited, due to (i) the design complexity of an optimized device able to reach a resolution in the order of ≈ 10 μm and (ii) limitations in available neutron flux. Here we propose a simple addition, based on a Fibre Optics Taper (FOT), that can be easily attached to an already existing scintillator-camera imaging detector in order to efficiently increase its spatial resolution and hence boost the capability of an instrument into high resolution applications.

In-situ investigation of water distribution in polymer electrolyte membrane fuel cells using high-resolution neutron tomography with 6.5 µm pixel size

In this feasibility study, high-resolution neutron tomography is used to investigate the water distribution in polymer electrolyte membrane fuel cells (PEMFCs). Two PEMFCs were built up with two different gas diffusion layers (GDLs) namely Sigracet® SGL-25BC and Freudenberg H14C10, respectively. High-resolution neutron tomography has the ability to display the water distribution in the flow field channels and the GDLs, with very high accuracy. Here, we found that the water distribution in the cell equipped with the Freudenberg H14C10 material was much more homogenous compared to the cell with the SGL-25BC material.

Towards high-resolution neutron imaging on IMAT

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.

Neutron Imaging with Timepix Coupled Lithium Indium Diselenide

The material lithium indium diselenide, a single crystal neutron sensitive semiconductor, has demonstrated its capabilities as a high resolution imaging device. The sensor was prepared with a 55 μ m pitch array of gold contacts, designed to couple with the Timepix imaging ASIC. The resulting device was tested at the High Flux Isotope Reactor, demonstrating a response to cold neutrons when enriched in 95% 6 Li. The imaging system performed a series of experiments resulting in a <200 μ m resolution limit with the Paul Scherrer Institute (PSI) Siemens star mask and a feature resolution of 34 μ m with a knife-edge test. Furthermore, the system was able to resolve the University of Tennessee logo inscribed into a 3D printed 1 cm 3 plastic block. This technology marks the application of high resolution neutron imaging using a direct readout semiconductor.

Determining Water Content and Distribution in PEMFCs to Predict Aging While in Storage

Proton Exchange Membrane Fuel Cells (PEMFCs) known for their use as portable energy-conversion devices have become increasingly more popular as backup power sources. Some backup power source applications require PEMFCs to startup within seconds after being stored for many years without any external aid. The ability to reach maximum power with a quick startup time in our design comes from the PEMFC being stored with water saturated membranes and catalyst layers. For the lowest overall resistance needed for an immediate startup, the water content of the membrane and catalyst layer ionomer should be maximized, which requires direct contact with liquid water i.e. Schroeder’s paradox. [1] However, any water collecting in the flow-fields or gas diffusion layers (GDLs) is detrimental, as it can obstruct reactant access. Consequently, the water distribution throughout the PEMFC during long-term storage is of critical interest for quick startup times. Previous studies have shown that water content and its distribution within a PEMFC is a good indicator of performance during both normal operation and accelerated stress testing. These studies have been mainly done using neutron imaging. [2,3] The measurements and analysis can be applied to PEMFCs hermetically sealed in storage. Before a PEMFC is stored, neutron imaging can be used to measure the water content and its distribution within the cell. It can then be measured and mapped for a series of identical PEMFCs stored for different lengths of time. Storage experiments have been performed by humidifying and hermetically sealing two identical single cells. Both cells were humidified by controlling the current using dry H2/O2 until a power of 2 W was reached and maintained for 60 seconds. It should be noted that for future experiments the cells will be stored in N2 to prevent any membrane permeation. Cell 1 was stored over night while cell 2 was stored for 14 days. For these cells, the goal was instant startup of at least 1.25 W at 0.5 V with 50 psig H2/O2 and maintaining that power output for at least 60 seconds. Figure 1 shows the results of both startups after storage. Cell 1 (solid grey line) after being stored overnight reached a peak power of 2 W in 1 second and maintained a power of 1.75 W for 120 seconds. Cell 2 (solid blue line) after being stored for 14 days reached a peak power of 3.25 W in 1 second however its power dropped rapidly and after 120 seconds reached the minimum power output of 1.25 W. Water movement within the cell during storage contributed to the different startup behaviors observed. With the use of high resolution neutron imaging in the z-direction (See Figure 2) the water content and distribution can be imaged through all components. The goal of this work is to store identical cells for varying lengths of time, compare the water content distribution in each cell and how it relates to the startup performance, and extrapolate how a cell will startup after multiple years in storage. Acknowledgments: This work is supported by the NNSA Engineering Campaign with long term funding from the Fuel Cell Technologies Office References T.A. Zawodzinski et al. Journal of The Electrochemical Society, 1993. 140 (4) 1041-1047.Spernjak, D. et al. Journal of The Electrochemical Society, 2009. 156 (1) B109-B117.Macauley, N. et al. Journal of The Electrochemical Society, 2016. 163 (13) F1317-F1329. Figure 1

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

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

(Invited) Imaging Fuel Cell Components: From Flow Field Channels to Catalyst Layers

Commercially viable polymer electrolyte membrane fuel cell (PEMFC) systems for transportation and stationary power applications require optimal combination of performance and durability at a competitive cost. Optimized water management across a fuel cell is key to improving performance and maintaining high conductivity of the ionomer in PEM and catalyst layers (CLs), while preventing excessive flooding in CLs, gas diffusion layers (GDLs), channels, and manifolds. Durability is also greatly affected by water transport as certain degradation mechanisms are accelerated depending on the humidity levels. As well, catalyst layers that suffered carbon corrosion due to long operation and/or high number of starts/stops are more susceptible to flooding. Imaging in situ and ex situ enables crucial insight into the microstructure of the fuel cell components and materials, associated water transport, and their effect on cell performance, dynamic response, and degradation mechanisms. Several case studies are presented to highlight the use of optical imaging, neutron imaging, and micro X-ray computed tomography (microXCT) to investigate fuel cell components across a range of length scales. Laboratory-scale microXCT instruments are used ex situ to resolve the three-dimensional structure of the GDL and electrodes, before and after various accelerated stress tests. Optical imaging in operating fuel cells offers a cost-effective combination of high temporal resolution (tens of frames per second) and high spatial resolution (several µm). The imaging requires special cell design with visual access to the imaged area (GDL surface and channels [1] or catalyst layer surface [2]). We employed optical visualization in a variety of studies, such as to visualize liquid water dynamics in the cathode and anode flow fields, or at the interface between the CL and the GDL. Besides water transport studies, optical imaging can quantify in-plane gas distribution in the flow fields during startups and shutdowns [3]. Neutron imaging is a powerful tool to visualize and quantify water transport in operating fuel cells. It has a high sensitivity to small amounts of water inside a cell, while having high transmission through the common fuel cell hardware. At a lower spatial resolution of 250 µm, neutron imaging is used to measure in-plane water distribution with high temporal resolution and large field of view of up to 20 cm by 20 cm. We studied the performance with novel NSTF (nano structured thin film) electrodes and GDL materials [4], and also visualized water and ice formation when cell was subjected to repeated starts at sub-freezing temperatures [5]. Since neutron imaging provides water content integrated along the neutron beam, we combined neutron imaging with the optical visualization to study water transport in different flow field geometries [6] as well as in an operating electrolyzer [7]. Such approach with simultaneous imaging provides additional information about the water location, and in certain situations allows distinguishing between channel and GDL water, or between anode and cathode channels and manifolds. High-resolution neutron imaging is able to measure water distribution across the cell thickness at spatial resolution as high as 10 µm. Image processing procedure is developed to measure the water uptake and observe Schroeder’s paradox in situ in PEMs [8,9]. Further, properties of the microporous layer (MPL) of the GDL were manipulated to prevent excessive flooding in cathode catalyst layers. Anode flooding is evidenced by optical visualization, simultaneous imaging, and high-resolution neutron imaging. Increased water transport across the membrane, from cathode to anode, can be detrimental as liquid water on the anode side may cause localized fuel starvation and cause irrecoverable degradation, similar to accelerated carbon corrosion during unassisted startups and shutdowns. However, for certain novel cathodes, which are prone to flooding, e.g. nano-structured thin film (NSTF) electrodes and non-precious group metal (non-PGM) catalysts, water removal through the anode has proven to be a viable option to improve the performance by reducing cathode water content. The authors acknowledge support from US Department of Energy EERE FCTO, Los Alamos National Laboratory LDRD (Laboratory Directed Research and Development) program, Federal Transit Administration, US Department of Commerce, and NIST Center for Neutron Research.

Progress in High-resolution Neutron Imaging at the Paul Scherrer Institut - The Neutron Microscope Project

Here we report the recent advances in the Neutron Microscope project at the Paul Scherrer Institut. We demonstrate the recent improvement on the capability of neutron imaging that allows us to acquire neutron images with isotropic spatial resolution of about 5 micrometres.

Acceleration of Liquid Water Removal from Cathode Electrode of PEFC by Combination of Channel Hydrophilization and Diffusion Medium Perforation

Water flooding at cathode catalyst layer (CL) is a critical issue for high power density and long-term operation of polymer electrolyte fuel cells (PEFCs). Especially, at high current densities, excessive water produced by oxygen reduction reaction (ORR) on cathode side is rapidly condensed and accumulated inside porous electrode. When open pores in CL and gas diffusion layer (GDL) are filled with liquid water, oxygen cannot be sufficiently fed to reaction sites. To alleviate this issue, it is necessary to design the optimum channel/GDL structure for accelerating through-plane water removal. Turhan et al. [1] investigated the through-plane liquid storage, transport and flooding mechanism as a function of channel wall wettability with the use of high-resolution neutron imaging. Results revealed that hydrophilization of cathode channel forms liquid film layers around channel walls, which is difficult to purge. However, hydrophilic channel effectively enhances liquid water suction from under-land locations into gas channels. Nishida et al. [2] also demonstrated that the through-plane water transport from GDL to channel is encouraged by channel hydrophilization, and the voltage drop due to flooding is reduced. On the other hand, several researchers presented a concept of perforated GDL structure to secure sufficient water passages through porous electrode. Gerteisen et al. [3] developed the customized GDL which is structured with water transport pathways by laser perforation, and revealed that this modified GDL improves the limiting current density of 8-22%. The perforated GDL structure beneficially enhances in-plane water discharge from porous media toward large penetration holes. However, the laser perforations may act as water pooling locations under high-current and high-humidity conditions because of the removal of PTFE coating, leading to performance degradation [4].This study proposes the novel channel/GDL combinational structure of channel hydrophilization and GDL perforation as shown in Fig. 1, in order to promote water removal through cathode electrode.Liquid water accumulated at the CL is discharged into the large penetration hole. Subsequently, the water droplets gathered in the hole gradually grow up and reach the hydrophilic channel. When these droplets are attached to the channel sidewall, they are immediately spread out on the hydrophilic surface and liquid films are moved upward along the sidewall. This water suction through the penetration hole effectively alleviates water flooding near the cathode CL. In this experiment, the liquid droplet behavior inside the cathode channel of an operating PEFC is firstly observed based on a cross-sectional visualization technique, and the effect of hydrophilic treatment of cathode channel on the enhancement of through-plane water transport and the performance improvement is investigated. Secondly, the impact of combinational structure of channel hydrophilization and GDL perforation on the reduction of water flooding is demonstrated under high-current and high-humidity conditions. The GDL perforation is carried by two different methods of electric discharge machining (EDM) and manual micro-drilling technique. The EDM method has the disadvantage of removing the PTFE coating of GDL, resulting in local water flooding. In contrast, the micro-drilling technique does not damage the hydrophobic treatment of GDL.Fig. 2 shows the changes of cell voltage during startup for two different channel/GDL structures. The red line denotes the result for the untreated channel/GDL structure; the blue line denotes the combinational structure with hydrophilized channel and perforated GDL. The effective electrode area of the cell is 2.88 cm2. The width, depth and total length of the gas channel are 1.0, 1.0 and 88.5 mm. The contact angle of water of the hydrophilized channel is 17 deg. In the modified cell, 35 penetration holes (Hole diameter: 0.3 mm) are installed into the cathode electrode by the micro-drilling method. The fuel cell operation is performed at 0.73 A/cm2 for 1000 s. The inlet gas temperature and humidity are 45 deg. C and 80% RH, respectively. As shown in the figure, in the case of the untreated structure, the cell voltage drastically drops after starting due to water flooding. On the other hand, the modified channel/GDL structure gradually recovers the voltage after t=150 s, because liquid water is removed from the cathode CL.

3D visualisation and dating of an embedded chert artefact from Barrow Island

This paper presents 3D visualisations of a non-local chert manuport embedded in a dune-deposited calcrete on Barrow Is., North West Australia. The use of non-destructive high-resolution neutron tomography provides critical visual evidence of any fracture surfaces on the embedded section of the chert, and of likely weathering before the chert manuport finally became cemented within the calcrete. Uranium-series dating of the calcrete and luminescence dating of the overlying dune sands indicates a likely age of ~41–14.5ka for the manuport, corresponding with the antiquity of the archaeology elsewhere on the island. The results highlight the potential of neutron tomography to resolve and document structural and morphological features of embedded archaeological materials without the need for invasive procedures.

CONRAD-2: the new neutron imaging instrument at the Helmholtz-Zentrum Berlin

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.

100 Hz neutron radiography at the BOA beamline using a parabolic focussing guide

The recent developments in scientific complementary metal oxide semiconductor (sCMOS) detector technology allow for imaging of relevant processes with very high temporal resolution with practically negligible readout time. However, it is neutron intensity that limits the high temporal resolution neutron imaging. In order to partially overcome the neutron intensity problem for the high temporal resolution imaging, a parabolic neutron focussing guide was utilized in the test arrangement and placed upstream the detector in such a manner that the focal point of the guide was positioned slightly behind the scintillator screen. In such a test arrangement, the neutron flux can be increased locally by about one order of magnitude, albeit with the reduced spatial resolution due to the increased divergence of the neutron beam. In a pilot test application, an in-situ titration system allowing for a remote delivery of well-defined volumes of liquids onto the sample stage was utilized. The process of droplets of water (H2O) falling into the container filled with heavy water (D2O) and the subsequent process of the interaction and mixing of the two liquids were imaged with temporal resolution of 0.01s.•Combination of neutron focussing device and use of sCMOS detector allows for very high temporal resolution neutron imaging to be achieved (albeit with reduced spatial resolution and field of view).•In-situ neutron imaging titration device for liquid interaction experiments.•Interaction of otherwise indiscernible liquids (H2O and D2O) visualized using neutron radiography with 0.01s temporal resolution.

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

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

Non-invasive archaeometallurgical approach to the investigations of bronze figurines using neutron, laser, and X-ray techniques

In the present work, structural imaging and non-invasive compositional analysis have been successfully combined in order to investigate three bronze figurines from the antiquarian collection of the Egyptian Museum of Florence. High-resolution neutron tomography was exploited for a thorough reading of the technological features of the mentioned copper alloy statuettes. At the same time portable XRF–XRD, Raman spectroscopy, laser-induced plasma spectroscopy, as well as time-of-flight neutron diffraction provided a powerful complementary analytical set for achieving reliable surface, depth profile, and bulk analyses. The proposed multi-analytical and non-invasive approach, involving neutron, X-ray, and laser techniques, allowed exhaustive identification of the raw materials and interpretation of the crafting processes used by ancient bronze smiths.

From nanopores to macropores: Fractal morphology of graphite

We present a comprehensive structural characterization of two different highly pure nuclear graphites that compasses all relevant length scales from nanometers to sub-mm. This has been achieved by combining several experiments and neutron techniques: Small Angle Neutron Scattering (SANS), high-resolution Spin Echo SANS (SESANS) and neutron imaging. In this way it is possible to probe an extraordinary broad range of 6 orders of magnitude in length from microscopic to macroscopic length scales. The results reveal a fractal structure that extends from ∼0.6nm to 0.6 mm and has surface and mass fractal dimensions both very close to 2.5, a value found for percolating clusters and fractured ranked surfaces in 3D.

Water Management in PEM Fuel Cells with Non-Precious Metal Catalyst Electrodes

The cost of polymer electrolyte membrane (PEM) fuel cells is a key challenge to developing commercially viable systems for transportation and stationary power applications. Non-precious group metal (non-PGM) catalysts offer a promising solution to lowering the system cost by eliminating the use of costly Pt-based catalysts. Recent studies have reported non-PGM catalysts with promising performance in fuel cells with Nafion® membranes and Nafion® as ionomer in electrodes [1]. Optimizing the electrode structure to improve transport and mitigate flooding is an ongoing task. The three-dimensional structure of the membrane-electrode assemblies (MEAs) was imaged using X-ray computed tomography (XCT), Figure 1. MEA 1 had conventional Pt/C cathode, while MEAs 2 and 3 had PANI-derived cathodes (with Fe salt also involved in the synthesis [1]). Cathode thickness was ~60 mm for all MEAs shown in Figure 1. All anodes were Pt/C based (bright regions in Figure 1 correspond to Pt in the electrodes). MEAs 1 and 2 had carbon-cloth gas diffusion layers (GDL), with microporous layer (MPL). MEA 3 had carbon-fiber-mat based GDLs with MPLs. Water distribution was recorded in situ, i.e. in H2/air operating fuel cells. We employed high-resolution neutron imaging at NIST [2], and small single-serpentine 2.5 cm2 cells [3], designed for the imaging of water profiles across the cell thickness (Figure 2). Cathode catalyst layer of non-PGM MEA2 had significantly higher (roughly double) water content compared to the Pt/C cathode in MEA 1. Pt and non-PGM electrodes were deliberately made with the similar thickness for straightforward comparison of the water content. The severe flooding in non-PGM cathode was correlated with the lower performance and higher mass-transport resistance measured from electrochemical impedance spectroscopy (EIS). Thus water management is critical to performance in fuel cells with non-PGM electrodes. Figure 1 also depicts an improvement in the fabrication of non-PGM MEAs, going from gas-diffusion electrodes (GDEs), MEAs 1 and 2, to the more recent MEAs with catalyst-coated membrane (CCM), MEA 3. The latter enables the use of modern GDL materials, with the goal to improve water management in non-PGM MEAs. To alleviate the cathode flooding levels, we employed novel GDL materials, known to help reduce water content in the cathode [4, 5] or to enhance water removal from cathode through the anode side [6]. Finally, we compare water management and fuel cell performance with varying non-PGM cathode thickness. The authors acknowledge funding from LANL Laboratory Directed Research and Development (LDRD) program, and US DOE EERE FCTO program. NIST authors were supported by the U.S. Department of Commerce, the NIST Radiation and Physics Division, the Director's office of NIST, the NIST Center for Neutron Research, and the Department of Energy interagency agreement No. DE_AI01-01EE50660.

Effect of Hydrophilic Treatment of Cathode Channel on Liquid Water Transport through Gas Diffusion Layer and Performance of PEFC

Water flooding and plugging on cathode side of polymer electrolyte fuel cells (PEFCs) lead to severe concentration overpotential due to oxygen transport limitation. To alleviate these issues, it is necessary to elucidate liquid water transport through cathode gas diffusion layer (GDL) and design the optimum structure of GDL and gas channel. In the previous works, many experimental efforts to visualize two-phase flow in operating PEFCs have been carried out by neutron [1], X-ray [2] and optical [3] techniques. However, most of the conventional visualization studies investigated only the water behavior along the flow direction of a PEFC. The through-plane behaviors of liquid droplets inside the cathode channel, including the emergence, growth and coalescence of droplets on the GDL surface and the attachment to the channel sidewall, cannot be exactly grasped. Turhan et al. [4] analyzed the through-plane liquid storage, transport and flooding mechanism as a function of channel wall hydrophobicity with the use of high-resolution neutron imaging. Results revealed that the channel wettability significantly affects the water transport from the diffusion media to the gas flow channels. Hydrophilic channel walls enhance the liquid water suction from under-the-land locations into the channels. In this study, the dynamic behaviors of liquid droplets inside the cathode channel are directly observed using a cross-sectional visualization cell, and the effect of hydrophilic treatment of cathode channel on the water transport through the GDL and the cell performance is investigated under operating conditions. The cross-sectional visualization technique is very useful to evaluate the growth and attachment behaviors of liquid droplets and the channel blockage owing to liquid water in the gas channel. In the experiment, the cell voltage and differential pressure between the cathode inlet and outlet are simultaneously measured, and the correlation between the liquid water behavior and the performance characteristics is discussed. Fig. 1 presents the time-series variation of the cell voltage and differential pressure of an operating PEFC for two different wettabilities of cathode channel wall. The contact angles of water of uncoated and hydrophilized channels are 76o and 17o, respectively. The fuel cell operation is performed at 0.5 A/cm2 for 1000 s. In the case of uncoated channel, the cell voltage remarkably decreases for the first 350 s at low air stoichiometry, because water flooding proceeds inside the cathode catalyst layer (CL) and GDL. Subsequently, both the voltage and pressure frequently fluctuate due to water plugging in the channels. On the other hand, the hydrophilic treatment of the cathode channels reduces the voltage drop due to flooding. Water droplets emerged from the GDL surface immediately attach to the hydrophilized channel sidewall and spread out on the wall surface. Therefore, the liquid water removal through the GDL is accelerated, and the water accumulation at the CL/GDL interface is alleviated. In addition, since the hydrophilic treatment of channels does not cause water plugging frequently, it drastically reduces the amplitude of voltage fluctuation. Hydrophilization of cathode channel effectively controls through-plane water transport and decreases both water flooding and plugging.

(Invited) Accurate Measurement of the Water Content of Proton-Exchange Membrane Fuel Cells Using Neutron Radiography

The water sorption of proton-exchange membranes (PEMs) was measured in situ using high-resolution neutron imaging in small-scale fuel cell test sections. A detailed characterization of the measurement uncertainties and corrections associated with the technique is presented. With high-resolution neutron-imaging detectors, the water distributions across N1140 and N117 Nafion membranes are resolved in vapor-sorption experiments and during fuel cell and hydrogen-pump operation and measurements are in reasonable agreement with a 1-D macrohomogeneous model. The measured in situ water content of a restricted membrane at 80 °C is shown to agree with ex situ gravimetric measurements of free-swelling membranes over a water activity range of 0.5 to 1.0 including at liquid equilibration. Schroeder’s paradox was verified by in situ water-content measurements which go from a high value at supersaturated or liquid conditions to a lower one with fully saturated vapor. At open circuit and during fuel cell operation, the measured water content indicates that the membrane is operating between the vapor- and liquid-equilibrated states.

Isotopically-enriched gadolinium-157 oxysulfide scintillator screens for the high-resolution neutron imaging

We demonstrate the feasibility of the production of isotopically-enriched gadolinium oxysulfide scintillator screens for the high spatial-resolution neutron imaging. Approximately 10g of 157Gd2O2S:Tb was produced in the form of fine powder (particle size approximately 2µm). The level of 157Gd enrichment was above 88%. Approximately 2.5µm thick 157Gd2O2S:Tb scintillator screens were produced and tested for the absorption power and the light output. The results are compared to the reference screens based on natGd2O2S:Tb. The isotopically enriched screens provided increase by a factor of 3.8 and 3.6 for the absorption power and the light output, respectively. The potential of the scintillator screens based on 157Gd2O2S phosphor for the purpose of the (high-resolution) neutron imaging is discussed.

IMAGINE: A Cold Neutron Imaging Station at the Laboratoire Léon Brillouin

A second cold neutron imaging station has been open to users at the Laboratoire Léon Brillouin. The station is designed for high resolution neutron imaging and tomography. The typical field of view is 100x100 mm2 with a spatial resolution of 100μm. Betterspatial resolutions (∼50μm) can be achieved when reducing the field of view down to 30x30mm2. The L/D ratio can be varied from 200 to1000with pinhole sizes ranging from 20 to7mm. Future upgrades will provide capabilities for energy resolved measurements using either a velocity selector or a double crystal monochromator. The possibility to perform polarized neutron experiments will also be provided next year.