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Water retention curves are essential for understanding the hydrologic behavior of partially saturated porous media and modeling flow and transport processes within the vadose zone. We directly measured the main drying and wetting branches of the average water retention function obtained using two-dimensional neutron radiography. Flint sand columns were saturated with water and then drained and rewetted under quasi-equilibrium conditions using a hanging water column setup. Digital images (2048 by 2048 pixels) of the transmitted flux of neutrons were acquired at each imposed matric potential (∼10–15 matric potential values per experiment) at the National Institute of Standards and Technology Center for Neutron Research BT-2 neutron imaging beam line. Volumetric water contents were calculated on a pixel-by-pixel basis using Beer-Lambert’s law after taking into account beam hardening and geometric corrections. To account for silica attenuation and remove scattering effects at high water contents, the volumetric water contents were normalized (to give relative saturations) by dividing the drying and wetting sequences of images by the images obtained at saturation and satiation, respectively. The resulting pixel values were then averaged and combined with information on the imposed basal matric potentials to give average water retention curves. The average relative saturations obtained by neutron radiography showed an approximate one-to-one relationship with the average values measured volumetrically using the hanging water column setup. There were no significant differences (P < 0.05) between the parameters of the van Genuchten equation fitted to the average neutron radiography data and those estimated from replicated hanging water column data. Our results indicate that neutron imaging is a very effective tool for quantifying the average water retention curve.

Neutrons and X-rays provide excellent complementary, nondestructive probes to understand internal structure of systems across engineering and material science. With its sensitivity to hydrogen, neutrons excel at separating fluids, such as water or oil, from solid and gas phases in three-phase systems whereas X-rays excel at identifying the solid phase. To fully leverage the complementarity of the two methods, the National Institute of Standards and Technology (NIST) has developed the Neutron and X-ray Tomography (NeXT) system which orients a microfocus X-ray generator orthogonally to a reactor sourced thermal neutron beam. This orientation allows for truly simultaneous acquisition of both modalities so that the multi-modal data sets of samples that are evolving with time or undergoing stochastic processes can be directly correlated. The NeXT system has been available for external researchers since 2015 through the NIST Center for Neutron Research user facility program. Significant efforts have resulted in distributable software packages to facilitate image denoising, tomography reconstruction, volume registration, and bivariate histogram segmentation. This paper will give an overview of the NeXT system, explain the process for bivariate histogram segmentation, and provide several examples of use cases for the system.

Fatigue in selective laser melted (SLM) and conventionally manufactured stainless steel (SS) 316 dogbones was studied with neutron imaging methods for attenuation, diffraction, and scattering. Neutron attenuation tomography and Bragg edge imaging did not reveal crack formation. Conversely, to efficiently detect the microcrack evolution, two methods of grating-based neutron interferometry, Talbot-Lau and far-field, were employed. Both interferometry methods detect early crack formation via the dark-field (scattering) images, especially for porous microstructures in the range of 0.6 μm to 2 μm. The dark-field image combines sensitivity to micrometer-sized scattering centers at crack formation with sub-millimeter imaging resolution. The crack formation observed with neutron interferometry dark-field was validated post-imaging with additional fatigue cycles to fracture. Further inspection was performed by scanning electron microscopy (SEM) and optical photography. In the two fatigued dogbones, SLM and conventional crack formation was identified to within 1 mm. Keywords: Additive manufacturing, Neutron interferometry, Bragg edge spectroscopy, Fatigue

We report on efforts to improve the achievable spatial resolution in neutron imaging by centroiding the scintillation light from gadolinium oxysulfide scintillators. The current state-of-the-art neutron imaging spatial resolution is about 10 μm, and many applications of neutron imaging would benefit from at least an order of magnitude improvement in the spatial resolution. The detector scheme that we have developed magnifies the scintillation light from a gadolinium oxysulfide scintillator, calculates the center of mass of the scintillation event, resulting in an event-based imaging detector with spatial resolution of about 2 μm.

As a neutron scatters from a target nucleus, there is a small but measurable effect caused by the interaction of the neutron’s magnetic dipole moment with that of the partially screened electric field of the nucleus. This spin-orbit interaction is typically referred to as Schwinger scattering and induces a small rotation of the neutron’s spin on the order of 10(−4) rad for Bragg diffraction from silicon. In our experiment, neutrons undergo greater than 100 successive Bragg reflections from the walls of a slotted, perfect-silicon crystal to amplify the total spin rotation. A magnetic field is employed to insure constructive addition as the neutron undergoes this series of reflections. The strength of the spin-orbit interaction, which is directly proportional to the electric field, was determined by measuring the rotation of the neutron’s spin-polarization vector. Our measurements show good agreement with the expected variation of this rotation with the applied magnetic field, while the magnitude of the rotation is ≈40 % larger than expected.

The predominant geometry for a neutron imaging experiment is that of a pinhole camera. This is primarily due to the difficulty in focusing neutrons due to the weak refractive index, which is also strongly chromatic. Proof of concept experiments demonstrated that neutron image forming lenses based on reflective Wolter mirrors can produce quantitative, high spatial resolution neutron images while also increasing the time resolution compared to the conventional pinhole camera geometry. Motivated by these results, we report the design of a neutron microscope where two Wolter mirrors replace condensing and objective lenses, in direct analogy with typical visible light microscopes. Ray tracing results indicate that this system will yield 3 μm spatial resolution images with an acquisition time of order

Image-forming focusing mirrors were employed to demonstrate their applicability to two different modalities of neutron imaging, phase imaging with a far-field interferometer, and magnetic-field imaging through the manipulation of the neutron beam polarization. For the magnetic imaging, the rotation of the neutron polarization in the magnetic field was measured by placing a solenoid at the focus of the mirrors. The beam was polarized upstream of the solenoid, while the spin analyzer was situated between the solenoid and the mirrors. Such a polarized neutron microscope provides a path toward considerably improved spatial resolution in neutron imaging of magnetic materials. For the phase imaging, we show that the focusing mirrors preserve the beam coherence and the path-length differences that give rise to the far-field moiré pattern. We demonstrated that the visibility of the moiré pattern is modified by small angle scattering from a highly porous foam. This experiment demonstrates the feasibility of using Wolter optics to significantly improve the spatial resolution of the far-field interferometer. Keywords: neutron imaging; Wolter optics; polarized neutron imaging; far-field interferometer, National Institute of Standards and Technology (U.S.) (Award 60NANB15D361)

Neutron imaging applications exploit the power of neutrons to penetrate through metals and measure small concentrations of hydrogen and lithium with high sensitivity. Recent advances in digital ima...

The NIST neutron imaging program will build a new imaging instrument in the NCNR guide hall at the end of the neutron guide NG-6, beginning operation in summer of 2015. The NG-6 guide has a spectrum that is strongly peaked at a neutron wavelength of 0.5 nm, with a fluence rate of 2 × 10 9 cm -2 s -1 before a bismuth filter that is cooled by liquid nitrogen. The instrument will be developed in a phased manner and with an emphasis on maintaining a flexible space to conduct experiments and test new instrument concepts. In the initial phase of the instrument, the available space will permit a flight path of about 9 m, and will provide a platform for standard neutron radiography and tomography, wavelength selective imaging with a double crystal monochromator, and phase imaging based on a Talbot-Lau interferometer. The novel feature of the instrument will be the incorporation of Wolter optics to create a neutron microscope. Initially, prototype optics will be used in the microscope configuration to assess optic characteristics and image acquisition techniques. In the final form, the microscope will enable users to acquire images with ∼10 μm resolution 10-100x faster than current practice, and with a 10x magnifying optic to acquire images with ∼1 μm spatial resolution with image acquisition time similar to that for current images with ∼10 μm resolution.

Dual mode tomography using neutrons and X-rays offers the potential of improved estimation of the composition of a sample from the complementary interaction of the two probes with the sample. We have developed a simultaneous neutron and 90 keV X-ray tomography system that is well suited to the study of porous media systems such as fuel cells, concrete, unconventional reservoir geologies, limestones, and other geological media. We present the characteristic performance of both the neutron and X-ray modalities. We illustrate the use of the simultaneous acquisition through improved phase identification in a concrete core.

The phenomenon of interference plays a crucial role in the field of precision measurement science. Wave-particle duality has expanded the well-known interference effects of electromagnetic waves to massive particles. The majority of the wave-particle interference experiments require a near monochromatic beam which limits its applications due to the resulting low intensity. Here we demonstrate white beam interference in the far-field regime using a two-phase-grating neutron interferometer and its application to phase-contrast imaging. The functionality of this interferometer is based on the universal moir\'e effect that allows us to improve upon the standard Lau setup. Interference fringes were observed with monochromatic and polychromatic neutron beams for both continuous and pulsed beams. Far-field neutron interferometry allows for the full utilization of intense neutron sources for precision measurements of gradient fields. It also overcomes the alignment, stability, and fabrication challenges associated with the more familiar perfect-crystal neutron interferometer, as well as avoids the loss of intensity due to the absorption analyzer grating requirement in Talbot-Lau interferometer.

The uptake of hydrogen by lanthanum pentanickel (LaNi5) to form lanthanum nickel hydride (LaNi5H6) is followed with three-dimensional imaging by neutron tomography. The hydrogen absorption process is slower than the time needed for acquiring a single radiograph, about 10 s, but fast relative to the time to acquire a fully-sampled tomographic data set, about 6000 s. A novel data acquisition scheme is used with angles based upon the Greek Golden ratio, a scheme which allows considerable flexibility in post-acquisition tomography reconstruction. Even with tomographic undersampling, the granular structure for the conversion of LaNi5 particles to LaNi5H6 particles is observed and visually tracked in 3D. Over the course of five sequential hydrogen uptake runs with various initial hydrogen pressures, some grains are repeatedly observed.

Neutron scans of an operating air–water contactor were performed at the NIST Center for Neutron Research (NCNR). Averaged radiographs were used to determine local and average liquid holdup profiles...

Commonly in neutron image experiments, the interpretation of the point spread function (PSF) is limited to describing the achievable spatial resolution in an image. In this article it is shown that for various PSF models, the resulting blurring due to the PSF affects the quantification of the neutron transmission of an object and that the effect is separate from the scattered neutron field from the sample. The effect is observed in several neutron imaging detector configurations using different neutron scintillators and light sensors. In the context of estimation of optical densities with an algorithm that assumes a parallel beam, the effect of blurring fractionates the neutron signal spatially and introduces an effective background that scales with the area of the detector illuminated by neutrons. Examples are provided that demonstrate that the illuminated field of view can alter the observed neutron transmission for nearly purely absorbing objects. It is found that by accurately modeling the PSF, image restoration methods can yield more accurate estimates of the neutron attenuation by an object.

Neutron imaging was been widely used to study the water distribution in proton exchange membrane fuel cell flow fields and gas diffusion layer. However, due to the limitation of spatial resolution, there has been little focus on the water transport process in the membrane and catalyst layer. Here we report on measurements made on thick membranes under saturation gradients which show no “jump condition” and on thick cathode catalyst layers to understand the water transport issues in a non-precious metal catalyst. Finally, we speculate on the possibility of obtaining neutron images with ~1 µm spatial resolution.

An experimental investigation on a water filled 6-turn oscillating heat pipe (OHP) was conducted using neutron imaging. Using the neutron images, a method was developed to determine the volume fraction of liquid phase in different portions of the OHP while in operation. The results show that the volume fraction of liquid phase is highly nonuniform once the thermally excited fluid motion starts. Over the heat input range studied, during the steady state oscillating motion in an OHP, the volume fraction distribution of liquid phase was always less than 2.5% in the evaporator and greater than 80% in the condenser. Using this method, the startup behavior, pulsing and pause motions, circulation, and the relationship between the pulsing motion and circulation and temperature variations in the OHP were all determined as well. There is a notable synchronization between the entrance of liquid into the evaporator portion of the heat pipe and temperature oscillations.

Neutron radiography and tomography were used to study the transient and steady-state distributions, respectively, of hydrogen within a prototypical, LaNi 4.78 Sn 0.22 -based hydrogen-storage bed during and after various absorption and desorption steps. It was shown that using deuterium instead of hydrogen enabled the imaging of thicker beds. These measurements serve to demonstrate the unique utility of neutron imaging as an important diagnostic tool for in situ , real-time characterization of hydrogen-concentration profiles in practical hydrogen-storage systems.

Recently, it has been demonstrated that a shearing type interferometer, using precision silicon gratings, enables one to image the gradient of neutron phase shift through an object and retrieve the phase via a simple one-dimensional integration of the gradient. To fully explore this new technique for potential future cold neutron imaging stations at the National Institute of Standards and Technology and the Korea Atomic Energy Research Institute, we have developed a prototype phase imaging station at a monochromatic cold neutron beamline in the NCNR neutron guide hall. We have designed the silicon gratings for a neutron wavelength of 0.44 nm and fabricated them using the state-of-the-art nanofabrication facility at the NIST Center for Nanoscale Science and Technology. Here we will discuss the experimental apparatus, as well as the recent experimental results obtained with this prototype apparatus. We will also present the data analysis method used for the phase retrieval, and discuss the accuracy of the method as well as the measurement sensitivity obtained using this method.

Neutron imaging has proven an invaluable tool for water metrology in operating proton exchange membrane fuel cells. Due to limitations in scintillator-based detector resolution, neutron imaging has been applied only to assessing the in-plane water distribution, without being able to distinguish water in the anode from the cathode. A new detector technology, based on micro-channel plates, enables a near order of magnitude improvement in the image resolution. This new detector technology will enable direct measurement of the through-plane water distribution in the gas diffusion layer, and enable the determination of the relative water content on the anode and cathode sides of a proton exchange membrane fuel cell. We report on the initial measurements with this new detector and discuss future measurement possibilities.

A new type of high performance and compact neutron collimator can be manufactured from Gd- or B-doped microchannel plates (MCPs). Structures only a few mm thick have very narrow rocking curves and high out-of-angle rejection ratios, as observed previously with a cold neutron beam. In this paper we present the results of measurements with a collimated (L/D ratio ~280:1) thermal neutron beam. MCP collimators doped with 3 mole% of natGd2O3 as well as doped with 10 mole% of 10B2O3 were calibrated for transmission versus tilt angle. The MCPs used in this study were only 0.6 and 0.8 mm thick with ~8.5 mum circular pores on 11.5 mum centers. All the measured rocking curves agree well with the theoretically predicted performance. Both experimental and modeling results indicate that very efficient MCP collimators (with

We have performed high precision measurements of the zero-energy neutron scattering amplitudes of gas phase molecular hydrogen, deuterium, and $^{3}$He using neutron interferometry. We find $b_{\mathit{np}}=(-3.7384 \pm 0.0020)$ fm\cite{Schoen03}, $b_{\mathit{nd}}=(6.6649 \pm 0.0040)$ fm\cite{Black03,Schoen03}, and $b_{n^{3}\textrm{He}} = (5.8572 \pm 0.0072)$ fm\cite{Huffman04}. When combined with the previous world data, properly corrected for small multiple scattering, radiative corrections, and local field effects from the theory of neutron optics and combined by the prescriptions of the Particle Data Group, the zero-energy scattering amplitudes are: $b_{\mathit{np}}=(-3.7389 \pm 0.0010)$ fm, $b_{\mathit{nd}}=(6.6683 \pm 0.0030)$ fm, and $b_{n^{3}\textrm{He}} = (5.853 \pm .007)$ fm. The precision of these measurements is now high enough to severely constrain NN few-body models. The n-d and n-$^{3}$He coherent neutron scattering amplitudes are both now in disagreement with the best current theories. The new values can be used as input for precision calculations of few body processes. This precision data is sensitive to small effects such as nuclear three-body forces, charge-symmetry breaking in the strong interaction, and residual electromagnetic effects not yet fully included in current models., Comment: 6 pages, 4 figures, submitted to Physica B as part of the Festschrift honouring Samuel A. Werner at the International Conference on Neutron Scattering 2005

Since the first observation of the phase shift of a neutron de Broglie wave induced by Earth's gravity, a series of increasingly sophisticated and precise experiments were carried out at the University of Missouri Research Reactor over a period of 1980–1997, now collectively called COW experiments. This class of neutron experiments is unique in that it represents a test of the principle of equivalence on a microscopic scale and that the outcome depends upon both the gravitational acceleration g and Planck's constant h . After all these efforts, however, there is still a 0.6–0.8% discrepancy between theory and experiment. The main correction is due to the bending of the interferometer crystal blades. The goal of this new attempt is to eliminate this effect by performing a gravitationally induced quantum interference experiment with a floating interferometer crystal. This means that the crystal is immersed in a liquid of equal density, i.e. a mixture of D 2 O+ZnBr 2 . The experiment will be carried out at the Neutron Interferometer and Optics Facility of the National Institute of Standards and Technology. This paper will give an overview of the previous experiments and present the experimental technique of the floating COW experiment.

The National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) is a national center that provides thermal and cold neutrons beams for activities such as condensed matter physics, materials science, nuclear chemistry, and biological science. Four beams are currently in use for fundamental physics experiments. These include a high-intensity polychromatic beam, a 0.496 nm monochromatic beam, a 0.89 nm monochromatic beam, and a neutron interferometer and optics facility. Experiments focus primarily on studies of the weak interaction using neutrons. This paper provides a general overview of the facilities and highlights some current experiments.

The design objective of the thermal neutron radiography facility at the National Institute of Standards and Technology (NIST) Center for Neutron Research was to provide a large beam diameter and a high fluence rate in order to produce images of dynamic systems. A thermal neutron beam with a 14 cm diameter thimble was chosen. The beam was initially filtered by a 10 cm thick single crystal bismuth filter cooled with liquid nitrogen. The beam exiting the port is shaped using either a 1 cm or 2 cm diameter pinhole to form a uniform high fluence rate beam at the sample. The resulting neutron beam at the sample has an L / D ratio of 280 with a fluence rate of 1.84×10 7 cm −2 s −1 and 560 with a fluence rate of 4.75×10 6 cm −2 s −1 uniformly spread over a 26 cm diameter beam. To capture the neutron beam image a scintillator and CCD camera is used. The current neutron camera system is limited to a 2.5 s frame rate; however, a high frame rate detector system based on amorphous silicon will allow frame rates to meet the design goal. Samples can be rotated and translated in situ for radiography and tomography applications. This facility became operational in early 2003. Since then the facility has been translated backwards by ≈2.13 m and 5 cm of bismuth was added to the filter. The design of this facility and the impact of the later changes are discussed.

This paper explores the method of neutron imaging as an experimental tool to perform in situ non-destructive analysis on an operating polymer electrolyte membrane hydrogen fuel cell. Neutrons are ideal for the imaging of hydrogen fuel cells because of their sensitivity to hydrogen-containing compounds such as water. This research focused on using imaging techniques to develop methods for testing and evaluating the water management system of a fuel cell. A real-time radiography dataset consisting of 1000 images at 2-s intervals was used to create a movie which showed water production, transport, and removal throughout the cell. This dataset was also analyzed to quantify and calculate the amount of water present in the cell at any time and masking techniques were used to differentiate between water in the cell flow channels and in the gas diffusion layer. Additionally, a tomography dataset allowed for the creation of a digital 3-dimensional (3-D) reconstruction of the dry cell which can be analyzed for structural defects.

In this paper we present a feasibility study of the use of phase contrast radiography in the examination of components from the hot-section of gas turbine engines. These components are usually made from dense materials (nickel or cobalt based superalloys) and, consequently, radiographic examination requires either high energy X-rays (above 60 keV) or neutrons. The relative merits of employing X-rays and neutrons for phase contrast radiography are compared. It is shown that, for similar penetration, neutrons offer better sensitivity and that it should be possible to detect even micron-wide cracks orientated perpendicular to the incident rays. Simulation shows that, for cracks parallel to the incident rays, crack growth in increments of microns can be resolved by monitoring the development of the Fresnel diffraction pattern. Some preliminary experimental results are also presented that demonstrate an improvement over conventional neutron radiography.

We report the results of an experiment which observed the 4π-symmetry of the neutron wave function under space rotation by the use of a slowly rotating magnetic field which trapped the precessing neutron spin and turned it in space.

A wavelength independent neutron interferometry technique has been applied to measure the scattering length densities Nb of liquid mixtures of H{sub 2}O-D{sub 2} O near room temperature. The experimental data have been compared to the conventional theory based on two separate liquids, with no deviations greater than 0.4{percent} observed. These results are not consistent with the predicted deviations due to quantum entanglement between protons and deuterons, which are at least an order of magnitude larger than our measured values. {copyright} {ital 1999} {ital The American Physical Society}

The neutron-interferometry (NI) technique provides a precise and direct way to measure the bound, coherent scattering lengths $b$ of low-energy neutrons in solids, liquids, or gases. The potential accuracy of NI to measure $b$ has not been fully realized in past experiments, due to systematic sources of error. We have used a method which eliminates two of the main sources of error to measure the scattering length of silicon with a relative standard uncertainty of 0.005%. The resulting value, $b=4.1507(2)\mathrm{fm},$ is in agreement with the current accepted value, but has an uncertainty five times smaller.

During the last two decades more than 35 fundamental quantum interference experiments have been performed using the perfect-silicon-crystal neutron interferometer. About one-half of these experiments have been carried out at the University of Missouri Research Reactor Center (MURR). In this paper we describe in some detail the instrumentation and the neutron optics of the two neutron interferometry setups currently situated at this 10 MW reactor.

Here we introduce a new method for coherent, reciprocal space neutron imaging. This new method overcomes the limitations of existing neutron imaging methods due to the resolution of the position sensitive detectors. The method implements a spatial encoding similar to that used in nuclear magnetic resonance (NMR) imaging or neutron Fourier spectroscopy. Spatial information is encoded in the phase of neutrons. In this paper we develop the theory, present preliminary results obtained by applying and refocusing a spatial phase gradient on the neutron beam and show simulations based on the experimental parameters of the neutron interferometer setup at the National Institute of Standards and Technology (NIST).

We present results of the first experiment clearly demarcating geometric and dynamical phases. These two phases arise from two distinct physical operations, a rotation and a linear translation, respectively, performed on two identical spin flippers in a neutron interferometer. A reversal of the current in one flipper results in a pure geometric phase shift of \ensuremath{\pi} radians. This observation constitutes the first direct verification of Pauli anticommutation, implemented in neutron interferometry.

A striking spectral-modulation effect has been observed by means of a proper postselection procedure under conditions where the spatial shift of the wave trains greatly exceeds the coherence length of the neutron beams traversing an interferometer. It is shown that Schr\"odinger-cat-like states are created by the superposition of two coherent states generated in the interferometer. These entangled states exhibit, under certain circumstances, characteristic squeezing phenomena, indicating a highly nonclassical behavior. Analogies with optical experiments are discussed.

The quantum mechanical phase shift for a massive particle due to gravity has been observed in a series of neutron interferometry experiments using perfect crystal silicon interferometers. While the results of these measurements are in qualitative agreement with the predictions of non-relativistic quantum mechanics and Newtonian gravity, there remains a very significant discrepancy between theory and experiment. It has been suggested that this discrepancy is due to a systematic effect related to the elastic deformation of the monolithic interferometer. In this work we describe X-ray measurements which indicate that such a systematic effect was overlooked in previous measurements. We conclude that the magnitude of these effects is sufficiently large to account for the current discrepancy between theory and experiment.

Neutron imaging as a method to perform in situ studies of hydrogen fuel cells, hydrogen storage devices, heat pipes, and batteries has made tremendous progress in recent years. Neutrons are useful to study light elements mixed with heavy Z elements where penetration by other forms of radiation is either impossible or incapable of contrasting the light elements. Useful spatial resolution available at neutron imaging facilities is now approaching 10 micrometers. Complimentary time resolution of 30 fps or greater is also possible with a spatial resolution approaching 300 micrometers. Here we will provide an overview of the technique of neutron imaging and experimental studies with neutrons at the National Institute of Standards and Technology. Examples of in situ studies of fuel cells, hydrogen storage devices, heat pipes and batteries will be discussed.

The use of thermal neutrons in contact radiography and tomography [Schlenker and Baruchel, Physica B 137, 309 (1986)] provides a powerful nondestructive analysis technique for materials that are difficult to study with x rays [Kirz et al., Quart. Rev. Biophys. 28, 33 (1995)]. Since x rays are strongly absorbed by the heavier elements and neutrons are preferentially scattered by light elements, neutron radiography is well suited to the visualization of light elements in the interior of metallic objects. In this letter, we demonstrate neutron radiography using a number of different contrast mechanisms. We find we are able to obtain radiographs showing features hitherto unobservable.

Neutron imaging has been demonstrated to be a powerful tool to measure the in situ water content of commercial proton exchange membrane fuel cells (PEMFCs) in two and three dimensions. The National Institute of Standards and Technology neutron imaging facility was designed to produce a high intensity, highly collimated neutron imaging beam to measure the water content of operating fuel cells. The details of the neutron optics and neutron detection are discussed in terms of the random uncertainty in measuring the liquid water thickness that is typical of operating PEMFCs.

The development of fuel cells and hydrogen storage materials will be one of the highest global research and development priorities for the foreseeable future. The particular abilities of neutrons to penetrate materials and to image hydrogen will make neutron imaging a key technique, allowing the in-situ study of real operational devices. This chapter describes the current state of the art in this field.

The application of neutron interferometry to the measurement of the atom density of polymer thin films (

Publisher’s Note: This paper, originally published on 5/13/2015, was replaced with a corrected/revised version on 7/1/2015. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. Plants exhibit complex responses to changes in environmental conditions such as radiant heat flux, water quality, airborne pollutants, soil contents. We seek to utilize the natural chemical and electrophysiological response of plants to develop novel plant-based sensor networks. Our present work focuses on plant responses to high-energy radiation – with the goal of monitoring natural plant responses for use as benchmarks for detection and dosimetry. For our study, we selected a plants cactus, Arabidopsis, Dwarf mango (pine), Euymus and Azela. We demonstrated that the ratio of Chlorophyll a to Chlorophyll b of the leaves has changed due to the exposure gradually come back to the normal stage after the radiation die. We used blue laser-induced blue fluorescence-emission spectra to characterize the pigment status of the trees. Upon blue laser excitation (400 nm) leaves show a fluorescence emission in the red spectral region between 650 and 800nm (chlorophyll fluorescence with maxima near 690nm and 735 nm). Sample tree subjects were placed at a distance of 1m from NIST-certified 241AmBe neutron source (30 mCi), capable of producing a neutron field of about 13 mrem/h. This corresponds to an actual absorbed dose of ~ 1 mrad/h. Our results shows that all plants are sensitive to nuclear radiation and some take longer time to recover and take less. We can use their characteristics to do differential detection and extract nuclear activity information out of measurement results avoid false alarms produced environmental changes. Certainly the ultimate verification can be obtained from genetic information, which only need to be done when we have seen noticeable changes on plant optical spectra, mechanical strength and electrical characteristics.

The neutron is electrically neutral, but its substructure consists of charged quarks so it may have an internal charge distribution. In fact it is known to have a negative mean square charge radius (MSCR), the second moment of the radial charge density. In other words the neutron has a positive core and negative skin. In the first Born approximation the neutron MSCR can be simply related to the neutron-electron scattering length b_ne. In the past this important quantity has been extracted from the energy dependence of the total transmission cross-section of neutrons on high-Z targets, a very difficult and complicated process. A few years ago S.A. Werner proposed a novel approach to measuring b_ne from the neutron's dynamical phase shift in a perfect crystal close to the Bragg condition. We are conducting an experiment based on this method at the NIST neutron interferometer which may lead to a five-fold improvement in precision of b_ne and hence the neutron MSCR., Comment: 5 pages, 2 figures

A measurement of the $n\text{\ensuremath{-}}^{3}\mathrm{He}$ coherent scattering length using neutron interferometry is reported. The result, ${b}_{c}=(5.8572\ifmmode\pm\else\textpm\fi{}0.0072)\phantom{\rule{0.3em}{0ex}}\mathrm{fm}$, improves the measured precision of any single measurement of ${b}_{c}$ by a factor of eight; the previous world average, ${b}_{c}=(5.74\ifmmode\pm\else\textpm\fi{}0.04)\phantom{\rule{0.3em}{0ex}}\mathrm{fm}$, now becomes ${b}_{c}=(5.853\ifmmode\pm\else\textpm\fi{}0.007)\phantom{\rule{0.3em}{0ex}}\mathrm{fm}$. Measurements of the $n\text{\ensuremath{-}}p$, $n\text{\ensuremath{-}}d$, and $n\text{\ensuremath{-}}^{3}\mathrm{He}$ coherent scattering lengths have now been performed using the same technique, thus allowing one to extract the scattering length ratios: parameters that minimize systematic errors. We obtain values of ${b}_{n^{3}\mathrm{He}}∕{b}_{np}=(\ensuremath{-}1.5668\ifmmode\pm\else\textpm\fi{}0.0021)$ and ${b}_{nd}∕{b}_{np}=(\ensuremath{-}1.7828\ifmmode\pm\else\textpm\fi{}0.0014)$. Using the new world average value of ${b}_{c}$ and recent high-precision spin-dependent scattering length data also determined by neutron optical techniques, we extract new values for the bound singlet and triple scattering lengths of ${b}_{0}=(9.949\ifmmode\pm\else\textpm\fi{}0.027)\phantom{\rule{0.3em}{0ex}}\mathrm{fm}$ and ${b}_{1}=(4.488\ifmmode\pm\else\textpm\fi{}0.017)\phantom{\rule{0.3em}{0ex}}\mathrm{fm}$ for the $n\text{\ensuremath{-}}^{3}\mathrm{He}$ system. The free nuclear singlet and triplet scattering lengths are ${a}_{0}=(7.456\ifmmode\pm\else\textpm\fi{}0.020)\phantom{\rule{0.3em}{0ex}}\mathrm{fm}$ and ${a}_{1}=(3.363\ifmmode\pm\else\textpm\fi{}0.013)\phantom{\rule{0.3em}{0ex}}\mathrm{fm}$. The coherent scattering cross section is ${\ensuremath{\sigma}}_{c}=(4.305\ifmmode\pm\else\textpm\fi{}0.007)\phantom{\rule{0.3em}{0ex}}\mathrm{b}$ and the total scattering cross section is ${\ensuremath{\sigma}}_{s}=(5.837\ifmmode\pm\else\textpm\fi{}0.014)\phantom{\rule{0.3em}{0ex}}\mathrm{b}$. Comparisons of ${a}_{0}$ and ${a}_{1}$ to the only existing high-precision theoretical predictions for the $n\text{\ensuremath{-}}^{3}\mathrm{He}$ system, calculated using a resonating group technique with nucleon-nucleon potentials incorporating three-nucleon forces, have been performed. Neutron scattering length measurements in few-body systems are now sensitive enough to probe small effects not yet adequately treated in present theoretical models.

In this paper, we will discuss a phase-contrast imaging method that avoids the complications of interferometry to provide phase contrast in weakly absorbing samples. A transversely coherent neutron beam is used with the traditional radiography scheme. Images taken with this scheme show dramatic intensity variations due to sharp changes in the neutron wave refractive index. With some numerical processing these images may be used to reconstruct a quantitative phase radiograph of specimens imaged with this technique.

We have performed high-precision measurements of the coherent neutron scattering lengths of gas phase molecular hydrogen and deuterium using neutron interferometry. After correcting for molecular binding and multiple scattering from the molecule, we find ${b}_{\mathrm{np}}=(\ensuremath{-}3.7384\ifmmode\pm\else\textpm\fi{}0.0020)\mathrm{fm}$ and ${b}_{\mathrm{nd}}=(6.6649\ifmmode\pm\else\textpm\fi{}0.0040)\mathrm{fm}.$ Our results are in agreement with the world average of previous measurements, ${b}_{\mathrm{np}}=(\ensuremath{-}3.7410\ifmmode\pm\else\textpm\fi{}0.0010)\mathrm{fm}$ and ${b}_{\mathrm{nd}}=(6.6727\ifmmode\pm\else\textpm\fi{}0.0045)\mathrm{fm}.$ The new world averages for the $n\ensuremath{-}p$ and $n\ensuremath{-}d$ coherent scattering lengths, including our new results, are ${b}_{\mathrm{np}}=(\ensuremath{-}3.7405\ifmmode\pm\else\textpm\fi{}0.0009)\mathrm{fm}$ and ${b}_{\mathrm{nd}}=(6.6683\ifmmode\pm\else\textpm\fi{}0.0030)\mathrm{fm}.$ We compare ${b}_{\mathrm{nd}}$ with the calculations of the doublet and quartet scattering lengths of several nucleon-nucleon potential models and show that almost all known calculations are in disagreement with the precisely measured linear combination corresponding to the coherent scattering length. Combining the world data on ${b}_{\mathrm{nd}}$ with the modern high-precision theoretical calculations of the quartet $n\ensuremath{-}d$ scattering lengths recently summarized by Friar et al., we deduce a new value for the doublet scattering length of ${}^{2}{a}_{\mathrm{nd}}=[0.645\ifmmode\pm\else\textpm\fi{}0.003(\mathrm{expt})\ifmmode\pm\else\textpm\fi{}0.007(\mathrm{theory})]\mathrm{fm}.$ This value is a factor of 4, more precise than the previously accepted value of ${}^{2}{a}_{\mathrm{nd}}=[0.65\ifmmode\pm\else\textpm\fi{}0.04(\mathrm{expt})]\mathrm{fm}.$ The current state of knowledge of scattering lengths in the related $p\ensuremath{-}d$ system, ideas for improving by a factor of 5 the accuracy of the ${b}_{\mathrm{np}}$ and ${b}_{\mathrm{nd}}$ measurements using neutron interferometry, and possibilities for further improvement of our knowledge of the coherent neutron scattering lengths of ${}^{3}\mathrm{H},$ ${}^{3}\mathrm{He},$ and ${}^{4}\mathrm{He}$ are discussed.

The program in fundamental neutron physics at the National Institute of Standards and Technology (NIST) began nearly two decades ago. The Neutron Interactions and Dosimetry Group currently maintains four neutron beam lines dedicated to studies of fundamental neutron interactions. The neutrons are provided by the NIST Center for Neutron Research, a national user facility for studies that include condensed matter physics, materials science, nuclear chemistry, and biological science. The beam lines for fundamental physics experiments include a high-intensity polychromatic beam, a 0.496 nm monochromatic beam, a 0.89 nm monochromatic beam, and a neutron interferometer and optics facility. This paper discusses some of the parameters of the beam lines along with brief presentations of some of the experiments performed at the facilities.

We have performed the first high precision measurement of the coherent neutron scattering length of deuterium in a pure sample using neutron interferometry. We find b_nd = (6.665 +/- 0.004) fm in agreement with the world average of previous measurements using different techniques, b_nd = (6.6730 +/- 0.0045) fm. We compare the new world average for the nd coherent scattering length b_nd = (6.669 +/- 0.003) fm to calculations of the doublet and quartet scattering lengths from several modern nucleon-nucleon potential models with three-nucleon force (3NF) additions and show that almost all theories are in serious disagreement with experiment. This comparison is a more stringent test of the models than past comparisons with the less precisely-determined nuclear doublet scattering length of a_nd = (0.65 +/- 0.04) fm., Comment: 4 pages, 4 figures

The interaction of neutrons with matter enables neutron radiography1 to complement X-ray radiography in analysing materials. Here we describe a simple quantitative method that provides a new contrast mechanism for neutron radiography and allows samples to be imaged at low radiation doses. Large phase shifts can be measured accurately from detailed structures not amenable to conventional techniques.

The neutron interferometry technique provides direct access to phase of the neutron wave. If properly applied, the use ofphase information in imaging materials can provide an advantage over normal intensity techniques, which use absorption toprovide image contrast. The National Institute of Standards and Technology Neutron Interferometry and Optics Facility hasbeen working on new methods and devices to exploit the neutron phase information to image materials. We will present herethe latest results ofthis effort and an overview ofthe instruments available at NIST for Neutron Phase Contrast Imaging.Keywords: neutron imaging, phase contrast imaging, neutron interferometry 1. INTRODUCTION The non-destructive imaging methods of neutron radiography and tomography have been applied to numerous problemsinvolving the imaging of materials'. These methods rely on relative changes in the intensity of the scattered beam, due toabsorption and scattering in the imaging material. In some materials this change in intensity is too low to produce significantcontrast between components in the sample which is being imaged. In such cases it might be possible to use the phase of thecoherently scattered wave to greatly enhance the contrast in the sample. Other authors have used both neutrons35, and x-rays9, to image materials with phase contrast techniques.Here we are interested in how the neutron wave is phase shifted by materials. Neutrons passing through matter can bescattered coherently and incoherently as well as absorbed. Generally the macroscopic manifestation of this process may bedescribed by a complex index ofrefraction46 given by,n =