Energy-resolved Neutron Imaging Research Articles

The energy-resolved neutron imaging instrument at the China spallation neutron source

The energy-resolved neutron imaging instrument (ERNI) is built on the number 13 beamline at the China Spallation Neutron Source (CSNS), which is the first instrument dedicated to pulsed neutron imaging in China. ERNI is designed as a multi-scale, multi-dimensional, multi-modality characterization platform. The analytical techniques will include conventional neutron radiography and tomography, Bragg-edge neutron imaging, neutron grating imaging, neutron resonance imaging, neutron diffraction, and complementary X-ray tomography. The spatial resolution for conventional neutron imaging is about 15 μm; the maximum field of view could achieve 200 mm × 200 mm; the spectral resolution is better than 0.5%. ERNI is expected to serve the growing multidisciplinary imaging user community from materials science, engineering, energy, cultural heritage, biology, geosciences, industry, and so on.

Development of a dual-mode energy-resolved neutron imaging detector: High spatial resolution and large field of view

Energy-resolved neutron imaging is an effective way to investigate the internal structure and residual stress of materials. Different sample sizes have varying requirements for the detector's imaging field of view (FOV) and spatial resolution. Therefore, a dual-mode energy-resolved neutron imaging detector was developed, which mainly consisted of a neutron scintillator screen, a mirror, imaging lenses, and a time-stamping optical fast camera. This detector could operate in a large FOV mode or a high spatial resolution mode. To evaluate the performance of the detector, the neutron wavelength spectra and the multiple spatial resolution tests were conducted at CSNS. The results demonstrated that the detector accurately measured the neutron wavelength spectra selected by a bandwidth chopper. The best spatial resolution was about 20 μm in high spatial resolution mode after event reconstruction, and a FOV of 45.0 mm × 45.0 mm was obtained in large FOV mode. The feasibility was validated to change the spatial resolution and FOV by replacing the scintillator screen and adjusting the lens magnification.

An energy resolved neutron imaging detector based on boron doped nMCP coupled with a time stamping optical camera

Energy resolved neutron imaging has developed rapidly due to its advantage on testing the inner structure of crystal samples. Neutron detector is one of the key components to determine the imaging results quality. The neutron sensitive microchannel plate (nMCP) has been widely used in energy resolved neutron imaging experiments because of the high spatial and timing resolution. However, the ability to adjust field-of-view (FOV) and spatial resolution has not been realized in the nMCP detector, which is an attractive capability in energy resolved neutron imaging experiments. In this paper, an energy resolved neutron imaging detector was developed by coupling nMCP with a time stamping camera. The neutrons were absorbed by nMCP and converted into light through a phosphor screen. Then the light was focused on the camera by optical lens. A data algorithm was designed to improve the data quality. By changing the magnification of the optical lens, large FOV (46mm diameter) and high spatial resolution (26 μm) were realized in the experiments at CSNS beamline 20. The energy resolved ability was demonstrated by a Bragg-edge transmission imaging experiment for aluminum and stainless-steel samples. The performance of this detector makes it a promising candidate used in energy resolved neutron imaging.

Tomographic reconstruction with Mantid Imaging

Mantid Imaging has been developed to provide a graphical reconstruction process for users of neutron imaging instruments to eliminate the need to fall back on commercial software. Mantid Imaging builds on algorithms provided by libraries including Astra Toolbox and Tomopy to offer noise reduction, artifact removal, alignment, filtered back projection and iterative reconstruction methods. Extra functionality was added by using algorithms from ALGOTOM for ring removal and from the Core Imaging Library (CIL) for regularised 3D reconstruction.Mantid Imaging 2.4 has recently been released. It is an open source Python GUI, runs under Linux and Windows and can easily be installed on end user systems. Mantid Imaging is aimed at users with no programming background and with little image processing experience. At ISIS Mantid Imaging runs on the ISIS-Data-Analysis-as-a-Service (IDAaaS) platform, which is remotely accessible with any modern web browser and gives users access to sufficient hardware resources to handle large datasets. Extensions of Mantid Imaging for energy-resolved neutron imaging are planned for the future.

Update of Bragg edge analysis software “GUI-RITS”

The energy-resolved neutron imaging system, RADEN at J-PARC, has been providing to users a Rietveld-type analysis code, RITS, for pulsed neutron Bragg-edge transmission (BET) imaging with a graphical user interface (GUI) version, for fitting spectral data obtained with this instrument. In the last year, we updated the computational platform of GUI-RITS software from Scientific Linux 6 (SL6) and Python 2 to Windows 10 and Python 3, and added some functions to improve usability. The license agreement for this updated software is the Berkeley Software Distribution (BSD) 2-Clause License (non-copyleft) and is currently available for download from the RADEN website.

In situ observation of crystal reorientation in polygranular graphite by synchrotron X-ray diffraction and neutron imaging

The capacity of polygranular graphite to accommodate strain is important to its use within structural components. This study has used in situ neutron and synchrotron X-ray experiments to demonstrate that reorientation of crystal domains accompanies the accommodation of applied mechanical strain in unirradiated Gilsocarbon (GCMB/IM24) graphite. Orientation changes were observed using 3D X-ray Diffraction, and local changes in neutron scattering were also observed with energy-resolved Bragg-edge neutron imaging. In both cases, this behaviour at the crystal level was partially recovered when the load was removed. This study provides new evidence for crystal deformation mechanisms that contribute to polycrystalline graphite's elastic non-linearity and the development of permanent set, which may also explain the effects of fast neutron irradiation on graphite elastic behaviour.

Silicon photomultiplier based scintillator thermal neutron detector for China Spallation Neutron Source (CSNS)

The energy-resolved neutron imaging spectrometer (ERNI) will be installed in 2022 according to the spectrometer construction plan of the China Spallation Neutron Source (CSNS). The instrument requires neutron detectors with the coverage area of approximately 4 m2 in 5°–170° neutron diffraction angle. The neutron detection efficiency needs to be better than 40% at 1 Å neutron wavelength. The spatial resolution should be better than 3 mm × 50 mm in the horizontal and vertical directions respectively. We develop a one-dimensional scintillator neutron detector which is composed of the 6LiF/ZnS (Ag) scintillation screens, the wavelength-shifting fiber (WLSF) array, the silicon photomultipliers (SiPMs), and the self-designed application-specific integrated circuit (ASIC) readout electronics. The pixel size of the detector is designed as 3 mm × 50 mm, and the neutron-sensitive area is 50 mm × 200 mm. The performance of the detector prototype is measured using neutron beam 20# of the CSNS. The maximum counting rate of 247 kHz, and the detection efficiency of 63% at 1.59 Å are obtained. The test results show that the performance of the detector fulfills the physical requirements of the ERNI under construction at the CSNS.

In Situ Observation of the Decomposition Process of Woodchips in Subcritical- and Supercritical Water by Neutron Imaging

In situ observation of the decomposition process of woodchips (cedar and Quercus acutissima) in subcritical- and supercritical water was performed by neutron imaging experiment. The woodchips and D2O were sealed into a stainless tube, and the tube was heated up to 500 °C by a block heater designed for neutron imaging. The neutron imaging experiment was performed in energy-resolved neutron imaging system (RADEN) of Japan Proton Accelerator Research Complex Material and Life Science Experimental Facility (J-PARC MLF). The decomposition processes of the woodchips in D2O solvent were visualized clearly in time-lapse images. The outside of the woodchips was partially broken at 300 °C. The woodchips have a porous structure at 450 °C, and D2O penetrates the pores. The skeleton of the woodchips remains even at 500 °C. The present study clarified the optimal temperature in the decomposition process to observe the status of the woodchips during the decomposition process. It has an advantage compared with a time-consuming of the batch process. It will be useful for the development of biomass processing technology using high-temperature and high-pressure water.

The multifunctional neutron imaging system at GPPD: Design, principles and applications

A multifunctional neutron imaging system (MNIS) has been built recently on the day-one instrument general purpose powder diffractometer (GPPD) at the China Spallation Neutron Source (CSNS). The sample position of MNIS is located three meters downstream of the diffraction sample position to maintain good imaging performance without changing the existing layout. MNIS can accommodate several significant neutron imaging technologies, including two-dimensional neutron radiation, three-dimensional computer tomography, neutron Talbot–Lau grating interferometer, and Bragg edge neutron imaging. The system has a largest field of view (FOV) of 6 × 6 cm2 and a best spatial resolution of 25μm by changing the magnification of the optical lens. The wavelength resolution is better than 0.2%. Additionally, MNIS serves as an initial validation for Energy-Resolved Neutron Imaging instrument (ERNI), a dedicated neutron imaging instrument currently under construction at CSNS.

Molecular specificity in neutron imaging: the case of hydrogen adsorption in metal organic frameworks.

Neutron imaging is the technique of choice for a number of in situ and operando applications, where a high penetration power is required. White-beam neutron imaging and energy-resolved Bragg edge imaging are successful techniques, the former for the detection of specific elements characterized by strong neutron attenuation and the latter for studying crystal structures. Here we discuss the capabilities of energy-selective neutron imaging taking advantage of the incoherent and inelastic scattering interactions in hydrogenous materials, as a way to obtain molecular-specific information about the composition of a given sample. While few examples from the available literature are discussed, a worked example is presented based on new experimental data on molecular-hydrogen adsorption and conversion in the HKUST-1 metal organic framework.

3D isotope density measurements by energy-resolved neutron imaging

Tools for three-dimensional elemental characterization are available on length scales ranging from individual atoms, using electrons as a probe, to micrometers with X-rays. However, for larger volumes up to millimeters or centimeters, quantitative measurements of elemental or isotope densities were hitherto only possible on the surface. Here, a novel quantitative elemental characterization method based on energy-resolved neutron imaging, utilizing the known neutron absorption cross sections with their ‘finger-print’ absorption resonance signatures, is demonstrated. Enabled by a pixilated time-of-flight neutron transmission detector installed at an intense short-pulsed spallation neutron source, for this demonstration 3.25 million state-of-the-art nuclear physics neutron transmission analyses were conducted to derive isotopic densities for five isotopes in 3D in a volume of 0.25 cm3. The tomographic reconstruction of the isotope densities provides elemental maps similar to X-ray microprobe maps for any cross section in the probed volume. The bulk isotopic density of a U-20Pu-10Zr-3Np-2Am nuclear transmutation fuel sample was measured, agrees well with mass-spectrometry and is evidence of the accuracy of the method.

Non-destructive characterization of the spatial variation of γ/γ′ lattice misfit in a single-crystal Ni-based superalloy by energy-resolved neutron imaging

Lattice misfit in nickel-based superalloys is one of the important microstructural parameters that control their mechanical properties, such as creep behaviour at high temperatures. Here, energy-resolved neutron imaging experiments are performed at a spallation neutron source to determine the spatial variation of lattice misfit on a second-generation nickel-based single-crystal superalloy specimen produced from a failed low-cycle fatigue specimen. The wavelength spectrum of the neutrons scattered by the specimen displays a large number of peaks, each corresponding to a spot in traditional Laue diffraction experiments. An analysis of the position and width of those Laue peaks in the transmission spectra allows determination of the lattice parameters of the γ and γ′ phases that compose the specimen, as well as the strain misfit and the misorientation between them. An analytical model is developed to describe the full wavelength pattern of Laue peaks arising from a specimen composed of two single crystals, and this model is used to perform least-squares refinements of the spectra measured at different positions of the specimen, with a spatial resolution of ∼500 × 500 µm. The local variations of the lattice parameter across the sample area were less than 4 mÅ for both phases, and the lattice misfit remains essentially constant at a value of 0.30 ± 0.03%, whilst the misorientation between the two phases is always smaller than 10′. By contrast, the relative misorientation between different parts of the specimen varies locally up to 1.5° on a scale of millimetres.

Energy-resolved neutron imaging with glass gas electron multiplier and dynamic time-over-threshold method

Energy-resolved neutron imaging with pulsed neutron source provides quantitative neutron imaging techniques such as Bragg-edge imaging, resonance absorption imaging, and polarized neutron imaging. Micro-pattern gaseous detectors (MPGDs) such as gas electron multipliers (GEMs) are widely used in neutron detection. In this research, we will report on the first demonstration of energy-resolved neutron imaging with a glass gas electron multiplier (G-GEM) and the dynamic time-over-threshold (dToT) signal processing method. We successfully performed energy-resolved neutron imaging at J-PARC MLF by measuring incident position and the Time-of-Flight (TOF) of each neutron simultaneously.

Investigation of radioactive samples for neutron capture reaction measurements using energy-resolved neutron imaging

To determine neutron capture cross-sections and elemental/isotopic compositions accurately via neutron capture reactions, shape effects caused by uniformity of samples must be considered. However, the estimation of shape effects is difficult to verify in some cases: sealed samples and valuable objects. In this study, the effects on sealed radioactive samples were estimated experimentally. A capability of energy-resolved neutron imaging enabled us to confirm significant localization of the sealed 129I sample non-destructively. It is revealed that shape effects should be corrected for obtaining accurate experimental results. Consequently, we conclude that energy-resolved neutron imaging will be effective to improve analytical accuracy.

(Invited) Synchrotron X-Ray and Pulsed Neutron Imaging of Water Transport Distribution in Fuel Cells

In order to realize a sustainable energy society, it is necessary to optimize energy and effectively utilize it by combining an electric grid and a hydrogen grid instead of the conventional fossil fuel-dependent type. Hydrogen has a high affinity with renewable energy and can be produced from various primary energies, so it is positioned as a promising energy in the future. We position fuel cell vehicles (FCVs) powered by hydrogen as the ultimate eco-friendly car, and are making vigorous efforts to develop high performance/reliability and low cost FCVs.Polymer electrolyte fuel cells (PEFCs) convert the chemical energy stored in hydrogen into electricity, with water as the only by-product. The inherent advantages of a PEFC include high electric energy efficiency and power density, low operating temperature and fast start-up, along with reduced environmental impact. PEFCs are regarded as a clean and efficient powertrain technology for automotive applications, serving as replacements for conventional internal combustion engines.PEFCs consist of an electrolyte membrane sandwiched between an anode and a cathode, and both the anode and cathode have laminated structures composed of a catalyst layer (CL) and gas channels in contact with a gas diffusion layer (GDL). When hydrogen and oxygen flow through the gas channels, an electrochemical reaction occurs in the CL, producing a by-product of water in addition to electrical power. The water generated by power generation then passes through the cathode GDL to the gas channel, and is finally discharged to the outside of the vehicle.The performance of fuel cells is greatly affected both by materials such as catalysts and electrolytes, and by how efficiently water generated by power generation is discharged, that is the essential role in water management function. To achieve a high-power density, it is really important to design sophisticated water management from water generation on the catalyst of FC to drainage outside the vehicle. Regarding the water management in PEFCs, it is necessary to manage it on a very wide scale from nanometer to millimeter. Based on the viewpoint that FC multiscale analysis linking materials, devices and vehicles is essential to achieve high performance by water management, we are currently constructing our original multiscale analysis combining quantum beam analysis using X-ray and neutron which enables liquid water visualization, as shown in Figure.In this presentation, I will exhibit two topics. First, I report improving water management in GDL through microporous layer (MPL) modifications [1]. Advanced 4D operando X-ray imaging (3D structure plus time) was employed to analyse the water content in GDLs, and demonstrated that the superior performance of cells with large MPL pores is due to the efficient formation of water pathways. The second is pulsed neutron imaging for differentiation of ice and liquid water distribution [2]. Energy-resolved neutron imaging is a methodology capable of distinguishing between liquid water and ice, and is effective for investigating ice formation in PEFCs operating in a subfreezing environment. We have enabled the observation of liquid water/ice distributions in a large field of view (300 mm × 300 mm) by manufacturing a sub-zero environment chamber that can be cooled down to -30 oC, as a step towards in situ visualition of full-size fuel cells.We hope that these studies will lead to the development of next generation FCVs. Figure 1

Monitoring residual strain relaxation and preferred grain orientation of additively manufactured Inconel 625 by in-situ neutron imaging

Microstructures produced by Additive Manufacturing (AM) techniques determine many characteristics of components produced by this particular manufacturing technique. Residual stress and texture are among those characteristics, which need to be optimized to meet dimensional and strength requirements. Post-build heat treatments are necessary to relief residual stresses, homogenize the microstructure and to develop the necessary microstructures (precipitation or solution hardening) for strength. Our focus in this study is the measurement of residual stresses during a vacuum stress relief (VSR) heat treatment. We employ the energy-resolved neutron imaging to investigate, in-situ, the uniformity of the as-built texture and to map the residual strain distributions within samples of Inconel 625 (IN625). The samples used in this study were printed using the powder-bed metal laser melting additive manufacturing technique. Strain and texture variations were measured at room temperature for the as-built samples as well as their changes during stress relief annealing at 700 °C and 875 °C in a vacuum furnace. The uniformity of crystalline plane distribution, from which texture can be inferred, was imaged with sub-mm spatial resolution for the entire sample area exceeding several square centimeters. Despite the limited accuracy of in-situ lattice strain reconstruction during sample annealing, the results indicate that most of the strain relaxation occurs at 700 °C within the first 2–3 h. Relaxation of the strain at 875 °C happened at a much faster rate. In addition, energy-resolved neutron imaging demonstrates the possibility to correlate the uniformity of grain orientation and the degree of texture variations with printing parameters, in particular the laser translation speed. Simulations of the AM build process were carried out to predict the residual stress distributions within the samples as a function of the build process parameters. Comparisons of the simulation results to the room temperature experimental measurements show good agreements when the simulation data are averaged over the volume of the part confirming the usefulness of the experiments for validating simulation results. The neutron imaging technique described in this study can be helpful for the evaluation of bulk crystallographic characteristics in AM printed materials and can be used as a guide for developing the heat treatment cycle and for validations of VSR simulation results.

In Situ Mechanical Loading and Neutron Bragg-edge Imaging, Applied to Polygranular Graphite On IMAT@ISIS

BackgroundBragg edge imaging have seen significant developments in the last decade with the availability of new time-resolved detectors, however, there have been no studies of changes in local coherent scattering from grain reorientation and deformation with load. Such damage accommodation mechanism may occur in (quasi)-brittle materials.ObjectiveWe developed a novel method using in-situ Bragg imaging at the ISIS spallation neutron and muon source on the IMAT (Imaging and MATerials science and engineering) instrument using an energy-resolved detector setup. We collected and analysed data of a proof-of-concept experiment demonstrating the use of the method.MethodsWe have developed a loading apparatus that addresses the constraints posed by Bragg imaging, allowing us to resolve features in the material microstructure. We use energy-resolved neutron imaging to obtain images in energy bins and we have developed a set of codes to register and correlate these images, as well as detect changes in local coherent scattering, in situ.ResultsPreliminary results from this method on Gilsocarbon nuclear graphite allow qualitative observation of local changes in Bragg contrast, which may be due to deformation or grain reorientation.ConclusionsWe have demonstrated that we can track changes in local coherent scattering under mechanical load, with sufficient resolution to track features with a size above 100 microns. This method, apparatus and accompanying codes may be used on the IMAT instruments by users interested to better understand deformation in their materials.

On the origin of mosaicity in directionally solidified Ni-base superalloys

This article addresses the formation of low angle grain boundaries which give rise to mosaicity, a phenomenon that has only recently received attention in the single crystal Ni-base superalloy field. In this work, post-mortem advanced microscopy characterisation techniques are employed to deduce the dendrite tip growth kinetics from transverse sections of a single crystal turbine blade. As a result, it has been possible to highlight the role of isotherm curvature in inducing lateral macro-segregation parallel to a growing solidification front. Using crystallographic data from time-of-flight energy-resolved neutron imaging and novel Bragg-dip post processing, it is established that lateral macro-segregation induces small angle grain boundaries which gives rise to mosaicity within single crystal Ni-base superalloys. Mosaicity demonstrates good correlation with the local primary spacing, where faster growing dendrites demonstrate greater deviation of 〈001〉 from the casting direction, as compared with those growing at a slower rate. In light of these findings, the origin of mosaicity and its implication to secondary grain formation is discussed.

The bandwidth chopper system design of the energy-resolved neutron imaging instrument at CSNS

An imaging beam line, Energy-Resolved Neutron Imaging instrument (ERNI) is under construction at China Spallation Neutron Source (CSNS). Here we describe the design of its bandwidth chopper system, such as the operation modes and the determination of the chopper parameters by theoretical calculations. The Monte Carlo simulations using McStas are performed to check the design of the bandwidth choppers system. The results of the theoretical calculations and the Monte Carlo simulations agree well in this work.

First neutron Bragg-edge imaging experimental results at CSNS* *Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFB0701903 and 2016YFA0401502), the National Natural Science Foundation of China (Grant No. 12041202), the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. 2017023), the Guangdong Natural Science Foundation, China (Grant No. 2016A030313129), and the Department

The neutron Bragg-edge imaging is expected to be a new non-destructive energy-resolved neutron imaging technique for quantitatively two-dimensional or three-dimensional visualizing crystallographic information in a bulk material, which could be benefited from pulsed neutron source. Here we build a Bragg-edge imaging system on the General Purpose Powder Diffractometer at the China Spallation Neutron Source. The residual strain mapping of a bent Q235 ferrite steel sample has been achieved with a spectral resolution of 0.15% by the time-of-flight neutron Bragg-edge imaging on this system. The results show its great potential applications in materials science and engineering.