Neutron Imaging Research Articles

The redesigned neutron imaging facility, NORMA at BNC, Budapest

The Budapest Neutron Center operates the cold neutron beam imaging station, Neutron Optics and Radiography for Material Analysis (NORMA), for non-destructive testing. For the NORMA station, there have been increasing requests to reach higher spatial resolution and the ability to follow time-dependent processes. Therefore, the system used successfully so far was completely redesigned and installed for a variety of tasks. The new system is based on the principle of three independent modules, allowing for highly configurable settings. It is to find the right balance between the necessary spatial resolution, a sufficiently shorter or longer temporal resolution, and a large enough field of view. The systematic study of the setups clearly shows the parameters’ effects, helping to make the right choice for the measurement tasks. Among the rarely investigated parameters, we studied both the effect of the pixel binning and the change in the lens f-stop value on the spatial resolution. The newly improved NORMA facility allows the acquisition of high-quality neutron images for planned observations, e.g., local water kinetics in fuel cells.

New Mini Neutron Tubes with Multiple Applications

Recent experimental investigations have demonstrated that a substantial amount of H−/D− ions can be formed by thermal desorption processes. Based on these new findings, new mini axial and coaxial-type neutron tubes have been developed for the production of high or low-energy neutrons via the d-d, d-10B, d-7Li or p-7Li nuclear reactions. By operating these mini neutron tubes with a high frequency AC high-voltage supply, short pulses of high intensity neutron beams can be generated. Multiple applications, such as carbon and well logging, neutron imaging, cancer therapy, medical isotope production, fission reactor start-up, fusion reactor material evaluation, homeland security and space exploration can be performed with the subcompact neutron generator system. It is shown that the performance of these new mini neutron tubes can exceed those of the conventional plasma-based neutron sources.

Model PEM water electrolyzer cell for studies of periodically alternating drainage/imbibition cycles

Investigating the counter-current two-phase flow within the anodic porous transport layer (PTL) of polymer electrolyte membrane water electrolyzers (PEMWEs) is a complex yet intriguing challenge. Until now, the gas-liquid invasion processes inside PTLs are only to a limited extent accessible under operation conditions, usually using sophisticated and expensive optical approaches, i.e., neutron imaging. We propose a model-supported experimental method with a fully operating microfluidic PEMWE, that allows to examine pore-scale oxygen-water distributions at the anode with high spatial and temporal resolution. The microfluidic cell is made of transparent Poly-Methyl-Methacrylate (PMMA), and the PTL is simplified by a quasi-2D pore network (PN) with a uniform pore-throat structure in the first preliminary study. The proposed setup is a significant advancement over previous studies, where gas was only injected at a constant flow rate from a single point. Test cases with current densities of 0.1, 1, and 2 A/cm2 and water flow rates of 1, 3, 5, and 10 ml/min were realized in the novel setup. We found periodically alternating invasion of oxygen (drainage) and water (imbibition), which were analyzed based on image sequences as well as voltage measurements. The experimental data is additionally supported by pore-scale Lattice Boltzmann (LB) and PN simulations. The preliminary results with the simplified PN structure are used to study the dominating transport mechanisms, revealing that drainage and imbibition occur simultaneously and are affected by evaporation and wetting liquid films formed in sharp pore corners. These phenomena are also expected to occur in more complex PTL structures. The preliminary results can, therefore, be regarded as an important basis for PTL studies, which are structurally more complex.

Design and Initial Tests of a Fast Neutron Radiography Detector Prototype with Silicon Photomultiplier Readouts

Among non-destructive testing (NDT) techniques, fast neutron radiography with a higher penetration capability has achieved rapid advancements. However, the application of the radiography detector in many fast neutron imaging systems is limited by unfavorable detection efficiency and imaging spatial resolution. In this paper, a fast neutron radiography detector was designed, which was composed of a pixelated EJ200 scintillator array, a 16 × 16 silicon photomultiplier (SiPM) array, and capacitive multiplexing network readout electronics. The main parameters of the detector were optimized using Monte Carlo simulations. In addition, the prototype of the detector was fabricated and tested under a 14 MeV D-T neutron source. The preliminary test results demonstrated that the spatial resolution of the prototype reached 1.2 mm. Moreover, the conflict between spatial resolution and detection efficiency could be mitigated by using a pixelated scintillator structure. Overall, SiPMs enabled the extensive application of the imaging system because of their excellent photon detection performance, relatively low price, and joint possibility for large areas.

Neutron imaging for cultural heritage at ANSTO

Neutron imaging for cultural heritage at ANSTO

Neutron tomography analysis of permeability‐enhancing additives in refractory castables

AbstractPolymeric fibers are often used as a drying additive for refractory castables because they can increase their permeability, reducing the risk of pressurization that is believed to trigger explosive spalling. Despite the potential of synthetic polymers to be engineered and obtain desired properties, the required parameters for inducing permeability enhancement remain unclear. This inhibits the development of novel designed drying additives and improvement of the numerical models. This work investigates the effect of polypropylene (PP), polyethylene (PE) and cellulose fibers on the water transport in refractory castables through rapid neutron tomography, enabling the in situ visualization of the water distribution, the drying front advance and the size, intensity and duration of moisture accumulation. PE and cellulose fibers accelerate drying fronts earlier than PP, in which PE exhibits larger moisture accumulation, residual moisture behind its drying front and a slower drying rate at higher temperatures despite the early water removal initiation. In contrast, cellulose emerged as a better candidate, due to a swelling–shrinkage based mechanism. The neutron tomography observations unveil the dynamic and intricate effect of fibers in the permeability, emphasizing that safer industrial processes require a deeper understanding of the underlying mechanisms to develop better fibers and accurate numerical models.

Application of Energy‐Resolving Neutron Imaging to Major‐Component Analyses of Materials Using Four‐Channel Superconducting Detector

We proposed a current‐biased kinetic inductance detector (CB‐KID) as a novel superconducting detector to construct a neutron transmission imager. The characteristics of a superconducting neutron detector have been systematically studied to improve a spatial resolution down to 10 in transmission imaging. In this study, we report the application of the energy‐resolving neutron imaging to investigate major components of materials by analyzing neutron transmission spectra from 1 meV to 500 keV. We succeeded in identifying that copper (Cu) and iron (Fe) are major components respectively in commercial nuts and screws as test samples with the aid of Rietveld imaging of transmission spectra (RITS) program in analyzing transmission spectra in longer wavelengths. The Ti screw was also confirmed by comparing the nuclear resonance absorption measurements and simulations in high‐energy regions. We demonstrated that our superconducting neutron detector is applicable to reveal the transmission spectra in the wide range from cold‐neutron energies to higher neutron energies even up to 500 keV. By selecting distinctive energy regions of pulsed neutrons, we succeeded in mapping the distribution of SmSn3 compound using the strong neutron absorption in samarium (Sm) and the selective nuclear‐resonance dips in Sm. By taking advantage of using CB‐KID in conducting neutron imaging, the CB‐KID method is extensively useful for various purposes in material sciences through energy‐selective neutron spectroscopy from 1 meV to 500 keV. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Developing a quantitative multimodal and multi-scale, fully non-destructive technique for the study of iron archaeological artefacts

This article presents the methodology and initial findings of the SNSF Sinergia project CORINT. The project's objective is to elucidate the corrosion mechanisms affecting iron-based structures entrapped in various porous media. This paper focuses specifically on iron archaeological artefacts (IAAs) in soil. A novel multimodal quantitative imaging technique, which integrates neutron and X-ray computed tomography (NX-CT), is under development for non-destructive examination of corrosion processes. The method involves registering and fusing neutron and X-ray tomography data, followed by Gaussian mixture model (GMM) clustering for phase segmentation. Imaging was conducted on two IAAs, Vrac C and BdC1. Additionally, random cross-sections of these samples underwent analysis through optical microscopy, µRaman spectroscopy, and SEM-EDS to characterize and correlate corrosion layers with NX-CT results. This study yields valuable insights into the corrosion of IAAs, enabling the non-destructive investigation of corrosion processes in porous media. The implications extend beyond the preservation of cultural heritage, to the examination of long-term corrosion behaviors in contemporary iron structures, steel within concrete, and nuclear waste disposal plans.

Investigating the flux pinning dependence on grain orientation in YBa2Cu3O7−δ using neutron tomography

In this study, we report the first case of non-destructive characterization of the dependence of the flux trapping mechanism on the grain properties of a bulk type II superconductor using a combination of polarized neutron tomography and diffraction contrast tomography. The high temperature superconductor, YBa2Cu3O7−δ, has been used in this study due to its viable commercial growth processes typically resulting in the production of polycrystalline specimens. The diffraction tomography revealed the pseudo-single crystal nature of the sample i.e. a polycrystalline sample with 47 composite grains having a maximum grain misorientation angle of 1.86°. Polarized neutron tomography was used for characterization of the flux trapped in the material after field cooling to 90.5 K in a field of 0.5 mT and switching off the field. A combination of the results from these two non-destructive characterization techniques indicate a correlation between the anisotropy of the trapped flux with the orientation of the grains in the material in addition to a preference for the flux trapping in the grain boundaries.

Mapping the elemental distribution in archaeological findings through advanced Neutron Resonance Transmission Imaging

This work highlights recent application of energy-selective neutron imaging at the ISIS Neutron and Muon Source, specifically focusing on the development of Neutron Resonance Transmission Imaging (NRTI) at the INES instrument. NRTI is a nuclear technique based on resonant neutron absorption reaction, which combines the sensitivity to elemental and isotopic composition with detailed morphological information, using the epithermal portion of the neutron flux available on the INES instrument at the ISIS facility. Unlike standard neutron radiography and tomography methods, NRTI preserves detailed time and energy information for each detector pixel, enabling enhanced visualisation of elemental distribution inside an object’s volume, with the potential for quantitative elemental analysis. These features combined with the non-destructiveness of NRTI make the method promising for applications in the field of Cultural Heritage, especially when it is employed in a multi-technique approach to provide complementary information about the composition and the crystalline structure of archaeological artefacts. A study related to Heritage Science is presented to demonstrate the effectiveness of NRTI in non-destructive investigations of inhomogeneous artefacts, specifically focusing on the excavation finds related to the first evidence of ancient brass production in Milan, Italy, during Roman times.

Source localization for neutron imaging systems using convolutional neural networks.

The nuclear imaging system at the National Ignition Facility (NIF) is a crucial diagnostic for determining the geometry of inertial confinement fusion implosions. The geometry is reconstructed from a neutron aperture image via a set of reconstruction algorithms using an iterative Bayesian inference approach. An important step in these reconstruction algorithms is finding the fusion source location within the camera field-of-view. Currently, source localization is achieved via an iterative optimization algorithm. In this paper, we introduce a machine learning approach for source localization. Specifically, we train a convolutional neural network to predict source locations given a neutron aperture image. We show that this approach decreases computation time by several orders of magnitude compared to the current optimization-based source localization while achieving similar accuracy on both synthetic data and a collection of recent NIF deuterium-tritium shots.

Polarized neutron imaging at NeXT (neutron and x-ray tomograph) at Institut Laue Langevin.

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

Neutron transmission imaging system with a superconducting kinetic inductance detector

Abstract We optimized the design and operating conditions of our superconducting neutron detector to improve spatial resolution. We obtained the best spatial resolution of 10 μm when a Gd Siemens star pattern was mounted in close contact with the detector. Although there is a trade-off between a spatial resolution and an easiness of replacing samples, we built our superconducting neutron imaging system for measuring in both the room-temperature samples with a proper collimation ratio L/D for achieving a reasonable spatial resolution and a cryogenic temperature with the best spatial resolution for certain purposes. In this study, we obtained neutron transmission images of various samples when they were cooled down with the superconducting neutron detector. We compared the effect of a different sample-detector distance on a spatial resolution when the samples were placed either at cryogenic temperature or at room temperature. We also confirmed that our CB-KID sensor was able to observe the neutron transmission coefficient over wider energies of pulsed neutrons. We found the appearance of clear Bragg dips by the measurements of natural FeS2 single crystals and succeeded in mapping the distribution of differently-oriented crystals by choosing several Bragg dips of the FeS2 crystals to compose the transmission images.

Characterization of a SiPM-based monolithic neutron scatter camera using dark counts

The Single Volume Scatter Camera (SVSC) Collaboration aims to develop portable neutron imaging systems for a variety of applications in nuclear non-proliferation. Conventional double-scatter neutron imagers are composed of several separate detector volumes organized in at least two planes. A neutron must scatter in two of these detector volumes for its initial trajectory to be reconstructed. As such, these systems typically have a large footprint and poor geometric efficiency. We report on the design and characterization of a prototype monolithic neutron scatter camera that is intended to significantly improve upon the geometrical shortcomings of conventional neutron cameras. The detector consists of a 50 mm×56 mm× 60 mm monolithic block of EJ-204 plastic scintillator instrumented on two faces with arrays of 64 Hamamatsu S13360-6075PE silicon photomultipliers (SiPMs). The electronic crosstalk is limited to < 5% between adjacent channels and < 0.1% between all other channel pairs. SiPMs introduce a significantly elevated dark count rate over PMTs, as well as correlated noise from after-pulsing and optical crosstalk. In this article, we characterize the dark count rate and optical crosstalk and present a modified event reconstruction likelihood function that accounts for them. We find that the average dark count rate per SiPM is 4.3 MHz with a standard deviation of 1.5 MHz among devices. The analysis method we employ to measure internal optical crosstalk also naturally yields the mean and width of the single-electron pulse height. We calculate separate contributions to the width of the single-electron pulse-height from electronic noise and avalanche fluctuations. We demonstrate a timing resolution for a single-photon pulse to be (128 ± 4) ps. Finally, coincidence analysis is employed to measure external (pixel-to-pixel) optical crosstalk. We present a map of the average external crosstalk probability between 2×4 groups of SiPMs, as well as the in-situ timing characteristics extracted from the coincidence analysis. Further work is needed to characterize the performance of the camera at reconstructing single- and double-site interactions, as well as image reconstruction.

Development of a phoswich imaging detector to simultaneously acquire neutron and gamma photon images

A neutron detector requires selectively detecting neutrons not detecting gamma photons. However, since gamma photons are commonly emitted from a neutron source, the separation of neutrons and gamma photons is sometimes difficult. To solve this problem, we developed a phoswich imaging detector that can simultaneously but independently acquire images of neutrons and gamma photons. The developed neutron imaging system consists of a lithium-containing silver doped zinc sulfide (Li–ZnS(Ag)) plate stacked on a cerium doped yttrium aluminum perovskite (YAP(Ce)) plate to form a phoswich detector, which is optically coupled to a position sensitive photomultiplier tube (PSPMT). Neutrons are detected by the Li–ZnS(Ag) plate while gamma photons are detected by the YAP(Ce) plate. The scintillation light from the Li–ZnS(Ag) and YAP(Ce) plates is detected by the PSPMT, and the position of interaction is calculated. Pulse shape discrimination is used to separate the images of neutrons and gamma photons. The spatial resolution of the imaging detector for neutrons is ∼2.6 mm FWHM, and the sensitivity for 252Cf neutrons at 2 cm from the source enclosed in 2-cm-thick polystyrene plates is 5.2 cps/MBq. The spatial resolution of the imaging detector for gamma photons is also ∼2.6 mm FWHM, and the sensitivity for 60Co gamma photons at 2 cm from the source within 2-cm-thick polystyrene plates is 375 cps/MBq. The contamination by gamma photons in the neutron window was negligible. The developed phoswich imaging detector can simultaneously and independently acquire the images of neutrons and gamma photons, and thus it will impact the relevant research and applications of neutron detectors and imaging.

Operando Neutron Imaging.

In the past, neutron imaging has been the little brother of advanced neutron spectroscopy techniques due to its apparent simplicity. However, this simplicity allows the studying of complex chemical and electrochemical processes and related devices even under harsh reaction conditions such as high pressure, high temperature, corrosive and/or air sensitive environments. We review a number of highly relevant case studies as archetypal examples of modern energy technology; that is heat storage, power-to-X, batteries, fuel cells, and catalysis. The promising results trigger the further development of neutron imaging towards a chemical imaging method.

Looking beyond X-ray: Neutron tomography analyses of Late Bronze Age weapons from the Somló Hill

Three spearheads and an arrowhead from the Somló Hill (Veszprém County, Hungary) Urnfield site are selected for X-ray radiography and neutron tomography analyses. The four weapons can be dated to the late phase of the Urnfield period between Ha B1 and Ha B2 and originate from different contexts: spearheads Nos. 1–2 from Hoard I, spearhead No. 3 from Hoard III, and an arrowhead (No. 4) as a stray find. Macroscopic characteristics of these newly discovered weapons attest to different stages of production and use, from as-cast to finished, used and heavily used products. The applied methods provide information on the inside of the objects, with special attention to the quality of the casting and traces of repair. Neutron tomography potentially offers an unbiased and quantifiable evaluation of the objects’ porosities and their levels from a modern industrial perspective. All three spearheads from Somló Hill showed different levels of porosity inside, the morphological characteristics of which suggest that they were probably caused by gas porosity. The long spearhead No. 1 from Somló Hill also shows traces of a misrun defect repaired by the cast-on technique. Traces of production and use suggest that except for one spearhead (No. 3), which was cast almost solid and showed high levels of porosity together with other types of defects, such as flashes and incomplete casting, all other studied objects were finished products used for combat and hunting.

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.

The importance of the adiabatic condition on polarized neutron imaging

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.

Phase-contrast neutron imaging compared with wave propagation and McStas simulations

Propagation-based phase contrast, for example in the form of edge enhancement contrast, is well established within X-ray imaging but is not widely used in neutron imaging. This technique can help increase the contrast of low-attenuation samples but may confuse quantitative absorption measurements. Therefore, it is important to understand the experimental parameters that cause and amplify or dampen this effect in order to optimize future experiments properly. Two simulation approaches have been investigated, a wave-based simulation and a particle-based simulation conducted in McStas [Willendrup &amp; Lefmann (2020). J. Neutron Res. 22, 1–16], and they are compared with experimental data. The experiment was done on a sample of metal foils with weakly and strongly neutron absorbing layers, which were measured while varying the rotation angle and propagation distance from the sample. The experimental data show multiple signals: attenuation, phase contrast and reflection. The wave model reproduces the sample attenuation and the phase peaks but it does not reproduce the behavior of these peaks as a function of rotation angle. The McStas simulation agrees better with the experimental data, as it reproduces attenuation, phase peaks and reflection, as well as the change in these signals as a function of rotation angle and distance. This suggests that the McStas simulation approach, where the particle description of the neutron facilitates the incorporation of multiple effects, is the most convenient way of modeling edge enhancement in neutron imaging.