Development of a fast neutron radiography converter using wavelength-shifting fibers

A fluorescent converter for fast neutron radiography (FNR) comprising a scintillator and hydrogen-rich resin has been developed and applied to electronic imaging. The rate of the reaction between fast neutrons and the converter is increased by thickening the converter, but its opaqueness attenuates emitted light photons before they reach its surface. To improve the luminosity of a fluorescent converter for FNR, a novel type of converter was designed in which wavelength-shifting fibers were adopted to transport radiated light to the observation end face. The performance of the converter was compared with that of a polypropylene-based fluorescent converter in an experiment conducted at the fast-neutron-source reactor YAYOI in the University of Tokyo.     

Investigation of fuel cells using scanning neutron imaging and a focusing neutron guide

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.     

Simultaneous dynamic neutron and gamma radiography

Equipment for dynamic neutron and gamma radiography has been developed at the 4.6 MW research reactor in Budapest, using thermal neutrons and gamma radiation obtained from the reactor. Radiography images are detected by scintillator screens and by low-light-level TV cameras, providing the possibility of visualizing medium-speed movements inside the investigated objects. The images are displayed on monitors and stored on video recorders. Some applications for nondestructive investigations are given.     

Time-of-flight neutron imaging at a continuous source: Proof of principle using a scintillator CCD imaging detector

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.     

Measurements of water distribution in through-plane direction of PEFC by using neutron radiography

Fuel gas (hydrogen gas) and oxidant gas (air) are supplied to a polymer electrolyte fuel cell (PEFC). Protons pass through the electrolyte membrane, and combine with oxygen to form water in the cathode reaction site. The generated water must be supplied appropriately to the membrane for proton conduction. On the other hand, the generated water may affect the fuel cell performances because of the blocking of oxygen from reaching the cathode reaction site. Therefore, water management in the PEFC is important, and water distribution during the operation in the through-plane direction has been of wide concern. In order to obtain the water distributions in a membrane electrode assembly (MEA) and a gas diffusion layer (GDL), a borescope system was newly employed using neutron radiography. The system could obtain the water distribution in the MEA and the GDL, and pixel size of 6.5 μm was achieved. Furthermore, the system was applied for a tilted converter system. The pixel of 1.0 μm at an angle of 81° was achieved, and improvement of the spatial resolution was confirmed.     

Real time imaging of two-dimensional iron oxide spherulite nanostructure formation

Nano Research - The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of view. Spherulite...     

Accelerator-based neutron tomography cooperating with X-ray radiography

Neutron resonance absorption spectroscopy (N-RAS) using a pulsed neutron source can be applied to time-of-flight (TOF) radiography, and the obtained parameters from the peak shape analysis can be reconstructed as the tomograms of nuclide distributions using computed tomography (CT). The problem is that the available spatial resolution is not sufficient for radiography imaging. In this study, we combined neutron and X-ray radiographies to improve the quantitative reconstruction of the neutron tomogram. The accelerator-based neutron source emits X-rays (or gamma-rays) at the same time the neutron pulse is emitted. We utilized the X-ray beam from the neutron source to obtain X-ray radiogram on the same beam line with neutron radiography and then reconstructed the neutron tomogram quantitatively with the help of a detailed sample internal structure obtained from the X-ray radiogram. We calculated the nuclide number density distribution tomogram using a statistical reconstruction procedure, which was easy to include in the structure model during the reconstruction. The obtained result of nuclide number density distribution showed good coincidence with the original object number density.     

X-ray imaging plate using CsBr:Eu phosphors for computed radiography

It is shown that X-ray-irradiated Eu-doped CsBr (CsBr:Eu) exhibits intense photostimulated luminescence (PSL). The peak wavelengths of PSL emission and stimulation spectra of CsBr:Eu phosphor ceramic samples are 450 and 690 nm, respectively. The dependence of PSL properties on preparing conditions of phosphor ceramic samples, such as Eu concentration, sintering temperature and sintering time, is studied. It is found that the PSL intensity of CsBr:Eu phosphor ceramics fabricated under optimum preparation condition is higher than that of commercially available imaging plates (IP) using BaFBr:Eu and BaFI:Eu. The image quality of the IP using CsBr:Eu phosphor film is better than that of commercially available IP.     

Real time atomic force microscopy imaging during nanogap formation by electromigration

We present real time atomic force microscopy imaging during nanogap fabrication by feedback controlled electromigration of a gold nanowire. The correlated measurements of electrical resistance and atomic force microscopy reveal that the major structural changes appear at the early stage of the process. Moreover, despite important morphological changes, the resistance of the nanowire shows a weak increase of just a few ohms. The detailed analysis of the atomic force microscopy images clearly shows that the electromigration process is strongly influenced by the initial microstructure of the nanowire.     

Quantitative kinetic analysis in a microfluidic device using frequency-domain fluorescence lifetime imaging

A novel microfluidic approach for the quantification of reaction kinetics is presented. A three-dimensional finite difference numerical simulation was developed in order to extract quantitative kinetic information from fluorescence lifetime imaging experimental data. This approach was first utilized for the study of a fluorescence quenching reaction within a microchannel; the lifetime of a fluorophore was used to map the diffusion of a quencher across the microchannel. The approach was then applied to a more complex chemical reaction between a fluorescent amine and an acid chloride, via numerical simulation the bimolecular rate constant for this reaction was obtained.     

Study of hydrogen effusion in austenitic stainless steel by time-resolved in-situ measurements using neutron radiography

The purpose of the present study was to show the feasibility of measuring hydrogen effusion in austenitic stainless steel (1.4301) using neutron radiography at the facility ANTARES of the research reactor FRM II of the Technische Universität München. This method is appropriate to measure in-situ hydrogen effusion for hydrogen concentrations as small as 20 ppm_H. Experiments were carried out in the temperature range from room temperature up to 533 K. The measurement principle is based on the parallel comparison of electrochemically hydrogen charged specimen with hydrogen-free reference specimen at the same temperature. This allows the determination of the hydrogen concentration in the specimens as a function of time and temperature. Separate hot carrier gas extraction experiments using the same temperature-time profiles as the radiography experiments have been used to calibrate the grey values of the neutron transmission images into hydrogen concentrations. It can be stated that the hydrogen effusion correlates with the specimen temperature.     

First demonstration of neutron resonance absorption imaging using a high-speed video camera in J-PARC

The neutron resonance absorption imaging technique with a high-speed video camera was successfully demonstrated at the beam line NOBORU, J-PARC. Pulsed neutrons were observed through several kinds of metal foils as a function of neutron time-of-flight by utilizing a high-speed neutron radiography system. A set of time-dependent images was obtained for each neutron pulse, and more than a thousand sets of images were recorded in total. The images with the same time frame were summed after the measurement. Then the authors obtained a set of images having enhanced contrast of sample foils around the resonance absorption energies of cobalt (132 eV), cadmium (28 eV), tantalum (4.3 and 10 eV), gold (4.9 eV) and indium (1.5 eV).     

The review and prospect of neutron radiography in China

Neutron radiography is one of radiography ray non-destructive testing. It is a valuable complementary of X and γ rays radiography. This paper briefly describes the history of neutron radiography in China, and introduces the status of neutron radiography facilities and their development in China.     

NECTAR—A fission neutron radiography and tomography facility

NECTAR (Neutron Computerized Tomography and Radiography) is a versatile facility for radiographic and tomographic investigations as well as for neutron activation experiments using fission neutrons.The radiation sources for this facility are two plates of highly enriched uranium situated in the moderator vessel in FRM II. Thermal neutrons originating from the main fuel element of the reactor generate in these plates fast neutrons. These can escape through a horizontal beam tube without moderation. The beam can be filtered and manipulated in order to reduce the accompanying gamma radiation and to match the specific experimental tasks.A summary of the main parameters required for experimental set-up and (quantitative) data evaluation is presented. The (measured) spectra of the neutron and gamma radiations are shown along with the effect of different filters on their behavior. The neutron and gamma fluxes, dose rates, L/D-ratios, etc. and the main parameters of the actually used detection systems for neutron imaging are given, too.     

Review and prospects of neutron radiography in the FRG

Even though the first neutron radiographs were made in the FRG by Kallmann and Kuhn nearly 50 years ago, this NDT method has never found wide-spread application here. In the past there have been facilities in Karlsruhe and Jülich for nuclear fuel examination, Siemens and AEG have attempted to use neutron radiography in industry and neutron radiography using a LINAC source has been investigated at Bundesanstalt für Material prüfung (BAM). With the development and availability of more powerful mobile sources and real-time inspection systems with neutron image intensifiers, neutron radiography may find greater application in industry. New applications for mobile neutron radiography will be in aircraft inspection, the testing of fibre-reinforced polymers and certain types of ceramics, civil engineering (concrete, natural stone and bricks), corrosion and lubricating investigations. In addition, many previous solutions in neutron radiography will come alive with the availability of inexpensive testing facilities.     

First study of macroscopic neutron dark field imaging using scattering grids

Instead of using the phase grating concept for dark field imaging, macroscopic scattering grids were employed at the ANTARES neutron imaging facility. Two Cadmium grids with a 1 mm gap and 1.2 mm bar were adjusted in a distance of only a few cm in order to block the direct beam. Thus, by placing the samples between these two grids only neutrons that were scattered at the samples were transmitted. A linear motion of the coupled grids allowed scanning across the samples and obtaining complete scattering projections, which delivered surprisingly sharp images. The geometric relation between grids permits determination of the transmitted scattering angles.     

Scheme for radiography/tomography with a low-brilliance neutron source at the CPHS

A cold neutron radiography/tomography instrument was designed and will soon undergo construction at the Compact Pulsed Hadron Source (CPHS) of Tsinghua University, China. In this paper, we report the physical design of the instrument and propose a scheme to implement several techniques at a later phase to enhance the utilization of the flux on larger samples. This includes code-aperture, grating-based imaging, prompt gamma-ray analysis and 3D emission CT.     

Advances in neutron imaging

Imaging techniques based on neutron beams are rapidly developing and have become versatile non-destructive analyzing tools in many research fields. Due to their intrinsic properties, neutrons differ strongly from electrons, protons or X-rays in terms of their interaction with matter: they penetrate deeply into most common metallic materials while they have a high sensitivity to light elements such as hydrogen, hydrogenous substances, or lithium. This makes neutrons perfectly suited probes for research on materials that are used for energy storage and conversion, e.g., batteries, hydrogen storage, fuel cells, etc. Moreover, their wave properties can be exploited to perform diffraction, phase-contrast and dark-field imaging experiments. Their magnetic moment allows for resolving magnetic properties in bulk samples. This review will focus on recent applications of neutron imaging techniques in both materials research and fundamental science illustrated by examples selected from different areas.     

Coded source neutron imaging with a MURA mask

In coded source neutron imaging the single aperture commonly used in neutron radiography is replaced with a coded mask. Using a coded source can improve the neutron flux at the sample plane when a very high L/D ratio is needed. The coded source imaging is a possible way to reduce the exposure time to get a neutron image with very high L/D ratio. A 17×17 modified uniformly redundant array coded source was tested in this work. There are 144 holes of 0.8 mm diameter on the coded source. The neutron flux from the coded source is as high as from a single 9.6 mm aperture, while its effective L/D is the same as in the case of a 0.8 mm aperture. The Richardson-Lucy maximum likelihood algorithm was used for image reconstruction. Compared to an in-line phase contrast neutron image taken with a 1 mm aperture, it takes much less time for the coded source to get an image of similar quality.     

Study of geometric imaging in radiography

This paper studies geometric imaging in radiography by both theory and experiment. The study is based on perspective geometry and uses computer analogue calculations and graphs. The previous method of calculating geometric unsharpness is two-dimensional and cannot perfectly reflect the three-dimensional case. The present author proposes a general principle for the three-dimensional image on a plane by projecting a radiative source onto an object and classifies images as pinhole, objective and transitional. It is shown that the projected images on a plane generated by projecting a rectangular source onto a circular transmissive element vary with the condition of the geometric images. Some new criteria for determining the performance of geometric imaging in radiographic inspection, such as the maximum radius R_J for pinhole image formation, the minimum radius R₀ for circular image formation, etc, are also proposed.