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Abstract: The accuracy of quantitative neutron transmission radiography can be substantially decreased if highly scattering materials, such as water or plastics, exist in the sample. There are currently two main solutions to this problem: either performing experiments at a large distance between the detector and the sample or employ some numerical correction techniques. In the former case, the spatial resolution is substantially reduced by the limited beam divergence, while the latter correction requires a priori information about the sample and is limited to distances of above ∼2cm. We demonstrate the feasibility of another technique, namely the possibility to remove the scattered neutron component from the transmitted neutron beam by a very compact polycapillary collimator. These ∼1mm thick devices can be placed between the sample and the detector and remove most of the neutrons scattered at angles larger than the acceptance angle of the collimator (typically 1°). No image distortions above ∼10μm scales are introduced by these collimators. The neutron transmission of highly scattering samples (water and plexiglass) is measured in our experiments with and without scatter rejection. In the latter case, the accuracy of measured transmission coefficient was substantially improved by our collimators. [Copyright &y& Elsevier]

Abstract: We present the use of helium-3 spin filters for polarized neutron imaging of magnetic phenomena. These polarization devices allow improvements in both spatial (factor of 2–3) and temporal (factor of ∼5) resolution compared with previously used solid-state benders. This set-up has been used to visualize small-scale magnetic features in an Fe65.7Co18Si0.8B15.5 foil with a thickness of 21–22μm and a saturation magnetization of 1.7T, and trapped magnetic flux in a superconducting lead cylinder. [Copyright &y& Elsevier]

Abstract: An optimized detector system that allows high-resolution neutron imaging with desired flexibility is described. The presented system can be adapted and integrated with standard CCD-based neutron detectors. Novel neutron scintillating materials with good photon discrimination and optical lens components are tested and optimized for high-resolution neutron tomographic purposes. The presented detector system provides variable field of view and can be used in combination with different techniques, including dark-field, energy-selective, and neutron spin polarized imaging. [Copyright &y& Elsevier]

Abstract: During the last decade neutron imaging has seen significant improvements in instrumentation, detection and spatial resolution. Additionally, a variety of new applications and methods have been explored. As a consequence of an outstanding development nowadays various techniques of neutron imaging go far beyond a two- and three-dimensional mapping of the attenuation coefficients for a broad range of samples. Neutron imaging has become sensitive to neutron scattering in the small angle scattering range as well as with respect to Bragg scattering. Corresponding methods potentially provide spatially resolved and volumetric data revealing microstructural inhomogeneities, texture variations, crystalline phase distributions and even strains in bulk samples. Other techniques allow for the detection of refractive index distribution through phase sensitive measurements and the utilization of polarized neutrons enables radiographic and tomographic investigations of magnetic fields and properties as well as electrical currents within massive samples. All these advanced methods utilize or depend on wavelength dependent signals, and are hence suited to profit significantly from pulsed neutron sources as will be discussed. [Copyright &y& Elsevier]

Abstract: The neutron tomography instrument CONRAD has been in operation since 2005 at the Hahn-Meitner research reactor at Helmholtz-Zentrum Berlin (HZB). Over the last 5 years, significant developmental work has been performed to expand the radiographic and tomographic capabilities of the beamline . New techniques have been implemented, including imaging with polarized neutrons , Bragg-edge mapping , high-resolution neutron imaging and grating interferometry . These methods have been provided to the user community as tools to help address scientific problems over a broad range of topics such as superconductivity, materials research, life sciences , cultural heritage and paleontology . Industrial applications including fuel cell research have also been improved through these new developments. Descriptions and parameters of the developed options will be presented, along with prominent examples. [Copyright &y& Elsevier]

Abstract: The X-ray photon counting hybrid pixel camera XPAD3-S is a promising detector for small animal X-ray radiography and tomography. The increasing interest in neutron imaging as a complementary approach to X-ray imaging motivates the study of the potentialities of this device for neutrons. To investigate this issue, we have studied the response of XPAD3-S to alpha particles and cold neutrons. The neutron detection was obtained with passive converters placed in front of the sensor. This choice permits to easily assemble 2D neutron sensitive imagers without size constraints; it penalizes however the detector efficiency with respect to other solutions. In this paper, we first analyze the detector response to alpha particles under several conditions, then we investigate its imaging performances and its detection efficiency for cold neutrons. Finally, we present the first XPAD3-S neutron tomography. Most of the results are validated by Monte Carlo simulations that will also permit to extrapolate the detector response to thermal neutrons. [Copyright &y& Elsevier]

Abstract: Edge enhancement is the main effect measured by the so-called inline or propagation-based neutron phase contrast imaging method. The effect has originally been explained by diffraction, and high spatial coherence has been claimed to be a necessary precondition. However, edge enhancement has also been found in conventional imaging with high resolution. In such cases the effects can produce artefacts and hinder quantification. In this letter the edge effects at cylindrical shaped samples and long straight edges have been studied in detail. The enhancement can be explained by refraction and total reflection. Using high-resolution imaging, where spatial resolutions better than 50μm could be achieved, refraction and total reflection peaks – similar to diffraction patterns – could be separated and distinguished. [Copyright &y& Elsevier]

Abstract: Scattered neutrons cause distortions and blurring in neutron radiography pictures taken at small distances between the investigated object and the detector. This defines one of the most significant problems in quantitative neutron radiography. The quantification of strong scattering materials such as hydrogenous materials—water, oil, plastic, etc.—with a high precision is very difficult due to the scattering effect in the radiography images. The scattering contribution in liquid test samples (H2O, D2O and a special type oil ISOPAR L) at different distances between the samples and the detector, the so-called Point Scattered Function (PScF), was calculated with the help of MCNP-4C Monte Carlo code. Corrections of real experimental data were performed using the calculated PScF. Some of the results as well as the correction algorithm will be presented. [Copyright &y& Elsevier]

Abstract: Glass-fiber-reinforced plastic laminates used for the insulation of Toroidal Field (TF) magnet-coils and fiber-reinforced silicon carbide ceramic composites used as structural material for the self-cooled Pb-17Li blanket module are attractive candidate materials for fusion reactors because of their high performance under extreme conditions. Porosity, which depends on the manufacturing process, and swelling of fiber-reinforced materials due to the high flux of radiation are the main problems. The aim of this study is to describe the experimental procedures of different imaging methods, and also to decide the most efficient imaging method for the investigations of the complex microstructure of fiber-reinforced materials. In this work, the fiber-reinforced composites were inspected with neutron and X-ray radiographies at ATI-Vienna and also at PSI-Villigen. A contrast enhancement at the edges can be achieved by means of phase contrast neutron radiography (NR), which is based on the wave properties of neutrons and arises from the neutron refraction (rather than attenuation). Elements having different refractive index within a sample cause a phase shift between coherent neutron waves. The degree of coherence can be determined by means of the coherence pattern caused by the sample, when a point source (pinhole) is used and the distance between source and sample is varied. [Copyright &y& Elsevier]

Abstract: The phase-contrast radiography is an edge-enhancement technique which allows to visualize objects providing very low contrast with the conventional absorption radiography technique. The image formation in this case is based on the phase variations transformed to intensity variations in a beam with a high lateral coherence by its transmission of the object. Due to the fact that neutrons could not be easily focused in a spot with a micrometric size like X-rays we need a small diaphragm and a large distance between the diaphragm and the sample in order to achieve a good lateral coherence length for the neutron phase-contrast radiographic experiments. The main beam parameters which generate some differences between the different beam facilities and influence the phase-contrast effect are the beam divergences and the beam spectra of each beam lines. Various examples of phase-contrast imaging performed at neutron beam lines with different beam parameters will be shown. The combination of the phase-contrast effect with the effect of image magnification due to the beam divergence which leads to an improvement in the image contrast and resolution will be presented in detail. [Copyright &y& Elsevier]

Abstract: The new cold neutron radiography and tomography facility at the Hahn-Meitner-Institut Berlin is suited for the investigation of components and materials from different industrial fields. The high-flux measuring position of the facility allows real-time imaging of fast dynamical processes. Cold neutrons interact stronger with the matter compared to thermal neutrons, which leads to a much better radiography contrast. Some examples of different industry applications like investigations on discharging of a Lithium battery or on oil sediments in a vent pipe are presented. [Copyright &y& Elsevier]

The phase-contrast imaging is based not only on the absorption contrast like in the conventional radiography but also on the contributions of the phase shifts induced by the propagation of a coherent radiation through the investigated sample. The strong phase changes on the borders between two media can be observed as sharp intensity variations on the radiography image. So the phase-contrast method is an edge-enhancement method which allows to visualize very fine structures where the conventional radiography provides unsatisfactory results.For the aims of the phase-contrast imaging a radiation with a high spatial but not necessarily chromatic coherence is required. In this way phase-contrast radiography experiments with a polychromatic thermal neutron beam possessing a high spatial transversal coherence can be performed. The reported results show that the developed phase-contrast neutron radiography can be used as a standard non-destructive investigation method. [Copyright &y& Elsevier]

The neutron attenuation coefficient drops for many solid materials quite drastically at a defined cold neutron energy known as a Bragg-cut-off in the cross-section diagrams. In many cases, the drop in attenuation for the corresponding elements is significant and this behavior can be exploited to change the material contrast in radiography and tomography images by modifying the spectrum of the applied neutron beam.The energy-dependent experiments were performed at the Prompt Gamma-ray Activation beam line where the irradiation position is at the end of a curved neutron guide, which delivers cold neutrons from the spallation source SINQ (PSI, Switzerland). This beam position gave the opportunity to perform radiography and tomography at low neutron energies. An effective monochromatization of the primary neutron beam was obtained by using a neutron velocity selector. The intensity of the modified beam was still reasonable for radiography images at different neutron energies and the experiments were performed in relatively short measuring times.A variety of samples were studied to illustrate possible applications of energy-selective radiography and tomography. This new neutron imaging technique provided encouraging results and projects of developing permanent facilities for such investigations at PSI and FRM II are under study. [Copyright &y& Elsevier]

The tomography setup developed at the PGA facility of the Swiss spallation source SINQ has provided encouraging results in the field of cold neutron imaging. Performances of the detection system based on a CCD camera and a converter screen have been recently improved using 6LiF/ZnS:Ag scintillators with different thickness. Indeed, reducing the layer of the scintillator improved considerably the spatial resolution while keeping a reasonable efficiency. Furthermore, a neutron velocity selector was temporarily added to the setup to perform radiography and tomography experiments with monochromatic neutron beams. Basic properties of transmitted beams were studied to assess the applicability of this device in neutron imaging. Of interest was the enhancement of the L/D-ratio by selecting neutron beams of short wavelengths. Cold neutron tomography demonstrated to be a useful technique in various spheres of activity, such as aerospatial industry or radioactive waste storage. Various applications of the neutron velocity selector are described in the second part, namely, New features in cold neutron radiography and tomography—Part II: Applied energy-selective neutron radiography and tomography. [Copyright &y& Elsevier]

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]

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]

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]

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]

Abstract: The investigation of soot sediments can be crucial for the development of improved components for combustion engines and for the identification of potential hazards. Here we present a number of exemplary studies of soot sediments in such components, which demonstrate the potential of neutron tomography in this field. Neutrons are well suited for imaging massive metal parts, which they can penetrate easily, allowing for imaging entire components with volumes of tens to hundreds of cubic centimeters non-destructively, whilst still being sensitive to lighter elements, in this case hydrogen-containing soot. Up-to-date techniques such as high-resolution and monochromatic neutron tomography have been applied in order to investigate soot sediments from fine particles in the pores of SiC diesel soot filters to massive structures in vent tubes of an aircraft. [Copyright &y& Elsevier]

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: 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]

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]

Abstract: We present two different methods to increase the size of available neutron beams in order to allow for the investigation of large objects. Application of these methods is demonstrated for radiographic imaging of fuel cells. The first approach is a scanning procedure based on the coordinated translation of detector and sample through the beam. Further advancement was achieved by installing a focusing neutron guide, which offers an expanded neutron beam size after diverging from a focused point source. [Copyright &y& Elsevier]

Abstract: Energy resolved imaging has recently gained attention for the potential of spatially resolved texture, crystallographic phase and strain investigations. Especially a time-of-flight (TOF) approach that takes maximum advantage of the new generation of pulsed spallation neutron sources is currently in the focus of investigations. Here, we present results of corresponding TOF measurements recorded at the continuous source of Helmholtz Center Berlin. The critical component for TOF imaging is however the availability of a high resolution imaging detector capable of the required time resolution. Here, a gated time-integrating detector without the corresponding continuous time resolution has been used and the measurements therefore have to be interpreted as proof-of-principle experiments as will be discussed. Measurements of different series of samples revealing structural differences related to their crystalline structure will be presented as well as a strain measurement on a dieless drawn wire. [Copyright &y& Elsevier]

Abstract: In the past, neutron imaging investigations have been mostly performed in “integrating mode”, which averages over the full applied neutron energy spectrum. This article describes four different methods and devices of obtaining energy selectivity in the thermal to cold energy range, which allow a new approach in neutron imaging. Two principles have been used and tested: (a) selection of neutrons by suppression of contribution of other spectral parts; (b) using the flight-time information in distance from the source. For the (a) option, three different devices have been exploited practically. Information about material properties can be revealed that cannot be obtained in integrating mode. The energy-dependent transmission measurements make use of the Bragg edges in the total cross-sections of materials. Energy-selective radiography has vast potential for contrast variation, and for mapping structural properties such as crystallographic texture and residual strains with high spatial resolution. The obtained images highlight new opportunities in materials and engineering research, in comparison and complementary to what can be obtained by neutron scattering. There is likely to be an increasing need for implementing time-of-flight neutron imaging at present and future pulsed spallation sources, where the energy range can be selected almost without limitations. In this paper we attempt to give an overview over the current state of the art of energy-selective imaging and the experimental configurations required. [Copyright &y& Elsevier]

The cold neutron tomography station operated at SINQ (Paul Scherrer Institute, Switzerland) is reviewed. The high neutron flux together with a set-up based on a scintillator screen and a CCD camera yielded fast and effective results with resolution down to 250 μm: tomography of small samples (up to 2 cm large) could be performed in less than an hour. The use of a velocity selector improved the contrast discrimination and allows dichromatic tomography. The station is moving to the new research reactor FRM-II (Garching, Germany) where its performances will be increased by the availability of a 5-times-higher cold neutron flux. [Copyright &y& Elsevier]