Neutron Imaging Facility 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.

Stochastic modeling of a neutron imaging center at the Brazilian Multipurpose Reactor

Neutron imaging is a non-destructive technique for analyzing a wide class of samples, such as archaeological or industrial material structures. In recent decades, technological advances have had a great impact on the neutron imaging technique, which has meant an evolution from simple radiographs using films (2D) to modern tomography systems with digital processing (3D). The 5 MW research nuclear reactor IEA-R1, which is located at the Instituto de Pesquisas Energéticas e Nucleares (IPEN) in Brazil, possesses a neutron imaging instrument with 1.0×106n/cm2s in the sample position. IEA-R1 is over 60 years old and the future of neutron science in Brazil, including imaging, will be expanded to a new facility called the Brazilian Multipurpose Reactor (RMB, Portuguese acronym), which will be built soon. The new reactor will house a suite of instruments at the Neutron National Laboratory, including the neutron imaging facility, viz., Neinei. Inspired by recent author’s works, we model the Neinei instrument through stochastic Monte Carlo simulations. We investigate the sensitivity of the neutron imaging technique parameter (L/D ratio) with the neutron flux, and the results are compared to data from the Neutra (PSI), Antares (FRM II), BT2 (NIST) and DINGO (OPAL) instruments. The results are promising and provide avenues for future improvements.

Investigation of Buddhist and Bon votive statues at the Very low power reactor VR-1

The nuclear analytical techniques are excellent tools for the investigation in various research disciplines, i.e. cultural heritage preservation, archaeology or anthropology. Most of these radioanalytical techniques require sufficient sources of radiation. So far, neutron imaging has mostly been used at high-power neutron sources, i.e. high-power research reactors. On the other hand, small nuclear research reactors can provide more options for investigations in multidisciplinary research. Since the development of the NIFFLER neutron imaging facility in 2020, neutron imaging has been one of the nuclear analytical methods used at the very low-power research reactor VR-1 of the Czech Technical University in Prague. This paper deals with the investigation of the internal structures of Buddhist and Bon votive statues from Central Asia at the Training reactor VR-1. The experimental investigation was conducted to explore the possibilities of using neutron imaging for cultural heritage research at very low-power research reactors such as the VR-1 reactor. The results of these unique experiments clearly showed the potential of the VR-1 reactor or possibly other very low-power research reactors in neutron imaging for multidisciplinary research, which can provide important data for anthropologists, archaeologists or experts in cultural heritage preservation.

Characterization of Transport Pathways in Electrolyzers Using Neutron and X-Ray Tomography

Electrolysis is a critical component to realizing a true green hydrogen economy. The performance and efficiency of an electrolyzer is directly tied to the multiphase transport that occurs within the porous transport layer (PTL). The PTLs must allow sufficient water transport to the catalyst layer to maintain the reaction while removing the product gases. PTLs are typically created from titanium foams or sintered from titanium powders or fibers. The resultant structure is heterogenous and requires 3D imaging to properly capture the pore structure and transport pathways. The use of titanium for the PTL can make it difficult to track the multiphase flow using X-rays alone as the X-ray energy required to penetrate 1 cm or more reduces the contrast between water and oxygen without the use of contrast agents that could affect the reaction. Neutrons provide a penetrating probe capable of imaging through titanium while having extreme sensitivity to water. Combing neutrons and high energy X-rays provides an easy way to identify all components in the PTL, i.e., the solid structure, oxygen, and water. The National Institute of Standards and Technology provides the Neutron Imaging Facility to the larger research community through the Center for Neutron Research facility user program. This instrument provides the ability to perform simultaneous neutron and X-ray tomography. Moving from 2D radiography to 3D tomography is critical to fully understand the influence of the PTL pore structure on the multiphase transport. This talk will give an overview of the instrument capabilities, showcase past success for neutron imaging of electrolyzers, and provide current progress on development of hardware and data reduction methods for simultaneous neutron and X-ray tomography of electrolyzers.

Evaluation of the delayed hydrogen cracking behavior and the hydrogen diffusion coefficient for different microstructures of the Zr-2.5%Nb alloy

The susceptibility of delayed hydride cracking (DHC) in the Zr-2.5%Nb alloy was evaluated in six microstructures produced from an extruded tube of Zr-2.5%Nb, which underwent different thermomechanical treatments, divided into two separate groups: Low temperature samples (LT) were heat-treated below the monotectoid temperature in the α-Zr + β-Nb field, and included pressure tube sample of CANDU-type material obtained through two different cold deformation methods, rolling and drawing, and stress-relieved at 400 °C for 24 h, and heat-treated samples at 600 °C/4 h. High-temperature samples (HT) were heat-treated in the β-Zr field at 900 °C/3 h, and two different cooling sequences up to room temperature.The increase in the ultimate tensile strength (UTS) and hardness due to metallurgical processing in LT materials made them more susceptible to DHC, reducing the stress intensity, KIH, from 11.8 to 8.5 MPa m0.5, together with an increase in crack propagation velocity from 1.6 10−8 to 4.5 10−8 m/s.In situ hydrogen diffusion experiments were performed at ANTARES, the cold neutron imaging facility at the FRM-2 reactor, on LT materials. These experiments demonstrated that the recrystallization treatment-induced discontinuity of the β-Zr phase in the parent material has a significant impact on hydrogen diffusion. It results in a 35% reduction in the diffusion coefficient compared to the parent material and a decrease in the terminal solid solubility (TSS) was observed. This resulted in a slight increase in KIH (7%), an increase in the hydride incubation time, and a decrease of about 20% in the crack propagation velocity. Under identical testing conditions, HT specimens were not susceptible to DHC phenomenon.

Development of a Neutron Imaging Facility at the Very Low Power Reactor VR-1

The paper describes the design and construction of a new neutron imaging facility at the very low-power research reactor VR-1. Neutron imaging has been under development at the VR-1 reactor as a new possible field of utilisation since 2020. The paper describes the main parts of the NIFFLER – “Neutron Imaging Facility for Learning and Research”. The detector system was designed in collaboration with the Technical University of Munich. The radial beam line modifications include different collimation ratios L/D, additional moderator configurations and the basic concept and design of the instrumentation. The paper also includes calculations of thermal neutron flux at the detector position for different radial beamline configurations. The results achieved at the training reactor VR-1 showed the potential of using neutron imaging at other low and very-low-power research reactors worldwide.

Hydrogen diffusion in Zr-2.5Nb pressure tubes specimens between 300°C-400°C by in-situ neutron imaging experiments

Zirconium (Zr) alloys are widely used in nuclear power plants as fuel cladding and are susceptible to hydrogen (H) degradation. For long operational service, Zr-based components can suffer a mechanism known as Delayed Hydride Cracking (DHC) associated to an increase of the crack propagation velocity by the re-orientation and precipitation of Zr hydride. In this process, the H mobility has a great influence. In the present work, the isothermal diffusion of H in Zr-2.5%Nb specimens obtained from a CANDU pressure tube were studied at consecutive temperatures of 300°C, 350°C, 375°C and 400°C. H content and mobility were quantified by in-situ neutron imaging experiments performed on ANTARES, the cold neutron imaging facility of FRM II. The time evolution of the H concentration across the specimen allowed the determination of diffusion coefficients, and an assessment of the limitations of existing models commonly used to describe H diffusion.

Failure characterization by pull-out test on structural inserts in sandwich panels used in the aerospace industry applying neutron imaging

In the present work, the failure of the inserts potted on the structural sandwich panel used in satellites was analysed. Inserts were tested by pull-out test to evaluate the strength of the joint between the potting mass and the sandwich panel. Neutron experiments were performed in NECTAR, the thermal neutron imaging facility at FRM II. Two series of specimens with dimensions of 10x10x2.5 cm3 and 5x5x2.5 cm3 were tested by applying different normal loads to detect singular points in the load-displacement curves. Images were acquired using thermal neutrons and filtering the beam obtaining images formed by gamma rays and epithermal neutrons. The filter was formed by a cadmiun (Cd) layer on the neutron beam. The results determined the usefulness of this characterization technique to analyse the dynamics failure of the insert union by the use of in-situ experiments in future studies.

Upgrading Neutron Imaging Facility at TRR-1/M1 Reactor

The neutron imaging system at Thai Research Reactor 1/Modification 1 (TRR-1/M1) is located at Thailand Institute of Nuclear Technology, Bangkok. It has been developed for research on non-destructive investigation using radiography and tomography techniques. The main instruments of the system consist of a neutron camera, a sample rotation system operated by in-house developed software, and a neutron shutter remotely controlled via a WIFI switch. In the first half of 2022, the TRR-1/M1 was temporarily shut down for annual maintenance. Meanwhile, additional shielding was installed in the imaging room for improving radiation safety. The current neutron camera was replaced with a new one to improve the imaging system performance. The camera performance, such as brightness and image quality, were investigated by varying the exposure time and imaging of the resolution test pattern, Siemens star, respectively. The results showed that the new camera set has higher brightness than the old one about 41% when compared to 70% grey value of 16 bit-format. The spatial resolution of 2D and 3D images were 0.59 mm and 1.37 mm, respectively. Moreover, the additional shields could reduce the radiation level around the reactor hall about 6-7 times. Then, neutron tomography using a new camera will be conducted to present the 3D visualization of various samples.

Development of in-situ Delayed Hydride Cracking tests using neutron imaging to study the H redistribution in Zr-2.5%Nb

Delayed Hydride Cracking (DHC) is a failure mechanism that occurs in Zr alloys under certain conditions of hydrogen concentration, temperature and stress gradient. In service, hydrogen produced by corrosion reaction can be incorporated in Zr alloys and if the solid solubility is exceeded, hydrogen precipitates as zirconium hydride. The presence of a stress concentrator, such as a crack, generates the hydrogen diffusion and precipitation to the high stress zone beginning the DHC process. In this work, in-situ DHC tests in air at 250°C were performed at ANTARES, the neutron imaging facility of the FRM-II reactor. Samples of Zr2.5%Nb produced from extruded tubes and pressure tubes were studied using a stress rig specially modified to perform DHC tests in the neutron beam. H redistribution during mechanical testing was followed in-situ by registering the changes in neutron transmission. The results were compared with the images obtained by light optical microscopy after the tests. The results highlight the capabilities of neutron imaging to analyze time-dependent H distribution during DHC crack growth.

New detector design of STORNI neutron imaging facility at RA-6 research reactor

The paper describes an upgrade of the neutron imaging facility at the RA-6 research reactor in Argentina. The RA-6 reactor is mainly used for education and training. Still, it is also equipped with several research facilities such as a neutron boron capture therapy facility, neutron activation analysis facility and neutron imaging facility. In 2022, the detection system of the neutron imaging facility was upgraded with the use of an astronomical CMOS camera and a 3D-printed housing. The upgrade was focused on improvements to the optical components resulting in better image quality and spatial resolution.

Evaluation of Neutron‐Radiation Tolerance of Lithium Indium Diselenide Semiconductors

Lithium indium diselenide (LISe) is a semiconductor that holds promise for neutron imaging sensor technologies because of its high neutron absorption efficiency and its corresponding ability to discriminate between gamma rays and neutrons. However, being a semiconductor, LISe may not be sufficiently radiation hard for practical application in radiation hard environments. Therefore, a systematic evaluation of the changes in material and electronic properties of LISe after high neutron fluence exposures is investigated. Herein, the characterization methods are utilized which included UV–vis, X‐ray diffraction, radioluminescence, Raman, fourier transform infrared spectroscopy (FTIR), current–voltage, and neutron sensing. Characteristics of LISe material that appeared in the literature are identified herein along with several that are expected to appear based on theoretical analyses. The results obtained show clear changes in the material properties of LISe after neutron exposure up to a fluence of 1016 n cm−2. However, LISe is still able to sense neutrons above the background at 1016 n cm−2, suggesting that LISe may be suitable for use in neutron imaging sensors at neutron imaging facilities.

The new INFN-CHNet neutron imaging facility

In this paper, NICHE (Neutron Imaging for Cultural HEritage), the new neutron imaging facility of the Italian National Institute of Nuclear Physics (INFN) is shortly presented. We report on the main features of the beamline, the specifications of the detection set-up, and the performances of the imaging system. NICHE is installed at the TRIGA reactor of LENA (Laboratorio Energia Nucleare Applicata) Pavia University laboratory (Italy). The imaging facility was designed during 2020, installed in the spring 2021, and has been in operation since May 2021. NICHE is the first Italian neutron imaging station open to national external users through the INFN-CHNet network application system. NICHE allows users to obtain neutron radiographies and tomographies, thus allowing for morphological characterisation of samples. First results to highlight the potential of the facility are reported. In particular, we show the first results about spatial resolution measurement and 3D reconstruction to provide morphological analysis capabilities.

New Neutron Imaging Facility NIFFLER at Very Low Power Reactor VR-1.

The paper describes the construction of the neutron imaging facility at the very low-power research reactor VR-1. The training reactor VR-1 is operated by the Czech Technical University in Prague, Czech Republic. It is mainly used for the education of students in the field of nuclear engineering as well as for the training of professionals. Neutron imaging is the new field of VR-1 reactor utilisation currently under development. Extremely low reactor power at the level of 100 W brought many challenges that were necessary to overcome to build and commission a sustainable neutron radiography facility. The paper describes the reactor's neutron flux verification and the basic concept and design of the neutron imaging instrumentation. The first experimental results were mainly dedicated to testing the detection system for different radial beam port configurations, different L/D ratios, and different exposure times. Preliminary results of neutron radiography and tomography measurements at VR-1 clearly showed the potential of using neutron imaging in low-power reactors such as the VR-1 reactor.

Neutron phase contrast imaging of PbWO4 crystals for G experiment test masses using a Talbot-Lau neutron interferometer

The use of transparent test/source masses can benefit future measurements of Newton’s gravitational constant G. Such transparent test mass materials can enable nondestructive, quantitative internal density gradient measurements using optical interferometry and allow in-situ optical metrology methods to be realized for the critical distance measurements often needed in a G apparatus. To confirm the sensitivity of such optical interferometry measurements to internal density gradients it is desirable to conduct a check with a totally independent technique. We present an upper bound on possible internal density gradients in lead tungstate (PbWO4) crystals using a Talbot-Lau neutron interferometer on the Cold Neutron Imaging Facility at NIST. We placed an upper bound on a fractional atomic density gradient in two PbWO4 test crystals of cm−1. This value is about two orders of magnitude smaller than required for G measurements. We discuss the implications of this result and of other nondestructive methods for characterization of internal density inhomogeneties which can be applied to test masses in G experiments.

Pore Segmentation Techniques for Low-Resolution Data: Application to the Neutron Tomography Data of Cement Materials.

The development of neutron imaging facilities provides a growing range of applications in different research fields. The significance of the obtained structural information, among others, depends on the reliability of phase segmentation. We focused on the problem of pore segmentation in low-resolution images and tomography data, taking into consideration possible image corruption in the neutron tomography experiment. Two pore segmentation techniques are proposed. They are the binarization of the enhanced contrast data using the global threshold, and the segmentation using the modified watershed technique—local threshold by watershed. The proposed techniques were compared with a conventional marker-based watershed on the test images simulating low-quality tomography data and on the neutron tomography data of the samples of magnesium potassium phosphate cement (MKP). The obtained results demonstrate the advantages of the proposed techniques over the conventional watershed-based approach.

Characterization of neutron imaging facility at Penn State Breazeale Nuclear Reactor

Characterization of neutron imaging facility at Penn State Breazeale Nuclear Reactor

TITAN neutron imaging facility performance

This paper presents the results of experiments on the TITAN facility to assess the quality of neutron imaging. A set of references samples developed by the Paul Scherrer Institute with the support of the IAEA was used. The results obtained demonstrated that the spatial resolution of the facility is 239μm for radiography and 358μm for tomography. The linear attenuation coefficients were determined for six materials. The maximum difference between the experimental values and the theoretical ones was 38%. The difference between the linear attenuation coefficients of neutron radiation from theoretical values is associated with the spectral dependence, due mainly to scattering and beam hardening that leads to deviation of the linear attenuation coefficient from the Beer–Lambert law. Tomography images were demonstrated that individual copper balls larger than 0.8 mm in diameter can be clearly recognized in a vial filled with balls.

Results from neutron imaging phase change experiments with LH2 and LCH4

Predicting evaporation and cryo-storage behavior of liquid hydrogen poses a challenge for both terrestrial energy infrastructure and long term space missions. The current understanding of cryogenic phase change and subsequent boil-off is limited, in part, because the values of accommodation coefficients (inputs to phase change models) are still lacking and experimental data to compute them are severely limited. In order to determine the accommodation coefficients, a new cryo/neutron imaging experiment was developed. Tests were conducted in the BT-2 Neutron Imaging Facility at the National Institute of Standards and Technology (NIST) by introducing propellant vapor into cylindrical aluminum (Al 6061) and stainless steel (SS 316) cells placed inside a 70 mm cryostat. Saturation points between 80 kPa - 230 kPa were tested for liquid H2 and CH4. Phase change was induced through precise control of pressure and/or temperature. Neutron imaging was used to visualize the liquid and evaporation/condensation rates were determined through image processing. Both hydrogen and methane are perfectly wetting fluids as evidenced by the formation of micro-scale thin film at the onset of condensation and varies in thickness with rate of phase change. The rates of phase change are a function of both the size of the container and the degree of offset from saturation. The unique experimental data, made available through a data repository, have the potential to serve as a bench mark for future studies or serve as a dataset for model validation.

A Preliminary Neutron Imaging Study of Moisture Transport in Cement-Based Materials on PKUNIFTY (A Compact Accelerator Based Neutron Imaging Facility at Peking University)

Understanding moisture transport is an important step in the study of the durability of cement-based materials. A neutron imaging detection method for water transport in cement-based materials, based on a compact neutron source is provided. We visualize the moisture transport and obtain the capillarity coefficients for different cement-based materials using PKUNIFTY.