Neutron CT Research Articles

G206 中性子ラジオグラフィを用いたダイナミックCT計測によるPEFC内水分布の三次元可視化・計測(OS5 水素・燃料電池)

Visualization of dynamic three-dimensional water behavior in a PEFC stack was carried out by neutron CT for clarifying water effects on performances of a Polymer Electrolyte Fuel Cell (PEFC) stack. Neutron radiography system at JRR-3 in Japan Atomic Energy Agency was used. An operating stack with three cells based on Japan Automobile Research Institute standard was visualized. A consecutive CT reconstruction method by rotating the fuel stack continuously was developed by using a neutron image intensifier and a C-MOS high speed video camera. The dynamic water behavior in channels in the operating PEFC stack was clearly visualized 15 sec in interval by the developed dynamic neutron CT system. From the CT reconstructed images, evaluation of water amount in each cell was carried out. It was shown that the water distribution in each cell was correlated well with power generation characteristics in each cell.

Visualization of Water Behavior in an Operating PEFC by Neutron Radiography

It is important to understand behavior of water which is generated by fuel cell operation to improve pelformance of the fuel cell. Neutron rays are transparent to most of metals and are attenuated by water. Therefore, neutron radiography is suitable to observe the water behavior in the fuel cell. The visualized and measurement results by using new neutron radiography techniques developed for the fuel cell researches were presented. Thmporal quantitative water thickness distributions in a JARI standard cell were measured. A network model was developed to simulate the gas flow velocity and the pressure distribution based on the measured results. Dynamic neutron CT was applied to 3-cell stack based on the JARI standard and the dynamic 3-D water behavior was observed every 15 seconds. The water distribution through plane in MEA and GDL in a small size fuel cell was measured by an imaging system using a bore-scope.

Reconstruction of limited computed tomography data of fuel cell components using Direct Iterative Reconstruction of Computed Tomography Trajectories

CT (computed tomography) reconstructions of fuel cell components of a yet unrivaled spatial resolution and quality are presented. This is achieved by application of the novel DIRECTT (Direct Iterative Reconstruction of Computed Tomography Trajectories) algorithm. We focus on two different key issues which essentially rule the fuel cell's durability on different length scales and physical interactions. On the resolution scale of some 100 μm agglomerations of condensed water in flow-field channels are detected by means of quasi- in situ neutron CT (after operation). Five orders of magnitude below nanometer sized Ru catalyst particles on carbon black support are visualized by electron tomography. Both types of experiments are especially adapted to the type of material involved but they are accompanied by severe deviations from ideal CT measuring conditions, as well. In order to overcome the tremendous reconstruction artifacts of standard algorithms, we employ DIRECTT which is described in detail. Comparisons of DIRECTT reconstructions to the conventional filtered back projection, prove the significant improvements in both experimental methods.

Dynamic neutron computer tomography technique forvelocity measurement in liquid metal flow- Fundamental PTV experiment -

The aim of this development is to visualize and measure the velocity distribution inliquid metal flow using the neutron beam with the high-speed imaging technique, computertomography (CT) technique and particle tracking velocimetry (PTV). Final research purpose isto obtain the velocity distribution and flow profile data of liquid metal flow in a heated rodbundle for development of the advanced fast breeder reactor (FBR) core. In this paper,visualization and measurement method using the high intensity and large size neutron beamport of the research reactor JRR-4, design and manufacturing of the experimental apparatus,spring model PTV method for this technique and results of the fundamental PTV experimentwere reported. The test section for the fundamental experiment was a revolving aluminumcolumn with cadmium tracers which simulated the liquid metal flow. As the result, cadmiumtracers buried in the column with the speed of 1.5 revolving per second could be visualized asthe 3D movie under 125Hz and 250Hz sampling conditions, the profile of the tracer could betraced, and fundamental velocity distribution measurement method could be conformed.

Three-dimensional observation of water distribution in PEFC by neutron CT

A polymer electrolyte fuel cell (PEFC) consists of a membrane electrode assembly (MEA), gas diffusion layers (GDL), hydrogen and oxygen supply channels. At the anode, protons and electrons are generated, while at the cathode the protons and electrons combine to form water. The condensed water may affect the fuel cell performance. In order to clarify the effect of water distribution on the PEFC performance, three-dimensional water distribution in the PEFC was visualized by using a neutron radiography facility at JRR-3 in JAEA. For observing the detailed water distribution, a small sized PEFC was designed. Size of the gas channel is 1 mm width and 0.5 mm depth. Thickness of the MEA and the GDL are about 50 and 200 μm. The electrode area is 0.35×3.5 cm 2. The PEFC was set on an automatic rotating stage, and a picture was taken every 2.25° by using a cooled CCD camera with grey scale of 16 bit. The exposure time was set at 15 s. Using the 80 pictures which correspond to 180°, a computed tomography (CT) was carried out. In order to observe water distribution with high spatial resolution, the LiF scintillator with a thickness of 50 μm was used. From the water distributions parallel and perpendicular to the MEA, existence of water around O-ring can be confirmed. However, the detailed distribution in the PEFC is difficult to obtain from the two-dimensional pictures. On the other hand, CT pictures make possible to obtain the three-dimensional water distribution. In this study, the spatial resolution of 76.5 μm was achieved, and existence of water in the PEFC could be confirmed.

Thermal Neutron Computed Tomography of Soil Water and Plant Roots

Neutron radiography is a noninvasive imaging technique that measures the attenuation of thermal neutrons, as is done with x‐ray and γ‐ray radiography, to characterize the internal composition of materials. Neutron and x‐ray imaging are complementary techniques, with neutron imaging especially well suited for materials containing H atoms and other low‐atomic‐weight attenuating materials. Although neutron computed tomography (NCT) techniques are routinely used in engineering, relatively little is known about their application to soils. We developed new techniques that use thermal neutron attenuation to measure the spatial and temporal distribution of water in soils and near roots at near 0.5‐mm spatial resolution or higher. The neutron source was a Mark II Triga Reactor at McClellan Nuclear Radiation Center in Sacramento, CA. After calibration using both deuterated and regular water, the effects of beam hardening and neutron scattering could be corrected for, provided that the total path length for a soil–water mixture does not exceed 1.0 cm, limiting soil sample thickness to about 2.5 cm. Using regular water, for a wide range of soil water content values, experiments demonstrated that NCT is sensitive to small changes in soil volumetric water content, allowing estimation of the spatial distribution of soil water, roots, and root water uptake. Although the spatial resolution of the applied NCT system was 80 μm, an error analysis showed that the averaging measurement volume should be not less than about 0.5 mm for the uncertainty in volumetric water content to be minimized to near 0.01 m3 m−3 A single root water uptake experiment with a corn (Zea mays L.) seedling demonstrated the successful application of NCT, with images showing spatially variable soil water content gradients in the rhizosphere and bulk soil.

Neutron CT enhancement by iterative de-blurring of neutron transmission images

It is well known that neutron radiography lags behind in terms of image spatial resolution compared to X-ray radiography. The reason for this is a combined effect of the beam line geometry, limited detector spatial resolution, scattering… etc. Although a lot of effort has been spent in the last 30 years to improve the resolution of classical digital images, the improvement of radiographic data is hardly ever done. In this paper, we explain why this is the case and come up with an approach to sharpen radiographs. An iterative, accelerated, damped algorithm has been developed to reduce blur artefacts in images obtained from neutron radiography facilities. In this technique, estimates of the radiographic data are convoluted with the detector response function and compared with the original blurred image. Successive iterated estimates of the un-blurred image are obtained by minimizing the square of the difference in pixel count between the original and blurred predicted image. This kind of Lucy–Richardson approach can be used effectively when the point-spread function PSF (blurring operator) is known, but little or no information is available for the noise. Additional optical system (e.g. camera) characteristics can be used as input parameters to improve the quality of the image restoration.

Application of very low energy neutron radiography with energy selection system using 4Qc(4m) supermirror

A high contrast neutron CT system is installed in the VCN/PF2 port of Institut Laue-Langevin and VCN port of Kyoto University Reactor (KUR). A converter+C-CCD system is used for the image detection. This system has an option of the energy selection system by neutron reflection on a 4Qc (4m) supermirror. The critical angle of the neutron reflection on this mirror is four times larger than that of natural nickel and the diameter is 20 cm. As the neutron reflection on a mirror removes faster neutrons, it can be used as a low pass filter of the neutron energy. The upper limit of the reflected neutron energy can be easily changed by the rotation of the mirror. As the application of this high contrast imaging system, the density nonuniformity of an aluminum welding sample can be shown by the refraction effect of very cold neutrons in VCN/PF2/ILL.

Application of neutron imaging plate and neutron CT methods on nuclear fuels and materials

Advanced neutron radiography techniques such as the neutron imaging plate (NIP) and neutron computed tomography (NCT) methods have been investigated in the practicability for the postirradiation examination (PIE). In current works, an unirradiated fuel rod was examined by NIP and NCT methods in order to collect the fundamental data for applying these techniques to the PIE. A fuel rod used is composed of seven-enriched UO/sub 2/ and two-natural UO/sub 2/ pellets with controlled sizes and shape that are loaded into a Zircaloy tube. The neutron radiography tests were performed by NIP and NCT methods at the 2nd Thermal Neutron Radiography Facility (TNRF-2) in the Japan Research Reactor (JRR)-3. In the NIP image of the fuel rod, the difference in the size, shape, and enrichment between the UO/sub 2/ pellets is obviously recognized. In the case of NCT method, the images clearly show the detailed shape of the cross section in both enriched and natural pellets; and difference in the enrichment between those pellets is also observed. In addition, size difference between fuel parts of specifications and those in NCT images is evaluated.

Comparison of X-ray and neutron tomography investigations of geological materials

This paper describes X-ray and neutron computer tomography (CT) experiments made on selected samples from geology. It gives a preliminary assessment of the utility of neutron tomography as a nondestructive means of examining geological materials, particularly as it complements X-ray tomography. Both methods show some advantages compared to the traditional two-dimensional analysis based on thin-sections of geologic samples. It is possible to obtain complete three-dimensional information with a resolution magnitude of tenths of a millimeter on the size and distribution of individual crystals within rock samples several centimeters in dimension. Due to basic differences of neutron and X-ray interaction with material the contrast variation between both imaging modalities highlights different structural information about the object.

Analysis of lithium and hydrogen movement in functional solid materials by neutron radiography

The principle and availability of Neutron Radiography are demonstrated. The technique is actually applied to obtain the images as to lithium in the oxide lithium ion conductors and/or hydrogen in the hydrogen storage alloys. From analysis of the lithium or hydrogen distribution, the ionic transport number and the diffusion coefficient can be calculated and the hydrogenation process is discussed. In the case imaging the special cross-section in the sample, Neutron Computed Tomography is more favorable. Here, it will be demonstrated using our actual experimental results that the NCT technique is also useful in the field of Solid State Ionics to clarify the ion distribution and movement.

Application of neutron radiography for estimating concentration and distribution of hydrogen in Zircaloy cladding tubes

Practicability of neutron imaging plate (IP) and computed tomography (CT) for estimating the distribution of the hydrogen concentration in Zircaloy tubes was investigated. Zircaloy tubes with controlled amount of hydrogen which is segregated at the periphery were prepared. The width of the hydrogen region is small around 0.1 mm. In IP image the small segregated hydrogen region is recognized, and the distribution of the hydrogen in the Zircaloy tubes is displayed. The hydrogen region is also recognized in a CT image of the tube containing large amount of hydrogen. These results show that both neutron IP and CT methods are applicable tools to estimate hydrogen distribution. A quantitative evaluation of the hydrogen concentration by those images is also discussed.

Analysis of lithium ion distribution in electrolyzed Li 1.33Ti 1.67O 4 by Neutron Computed Tomography

The principle and availability of Neutron Computed Tomography (NCT) were demonstrated. The technique was actually applied to visualize cross-sectional images as to lithium in electrolyzed spinel-type oxide, Li 1.33Ti 1.67O 4. From the analysis of the lithium distribution, the electric field formed in the oxide was figured. It was suggested that the electric field is the same as that formed in metal.

A preliminary study of CT imaging of water in a carnation flower

We present the trial to determine the water deletion part in a carnation flower tissue while drying by neutron computer tomography (CT). The flower part was fixed on a rotating disk and thermal neutrons were irradiated for 4 s per projection. The total neutron dose was 6.0×10 8 n/cm 2 per projection. The neutrons penetrating the sample were converted to photons by a fluorescence converter. The photon image was guided to a cooled CCD camera using two mirrors. The sample was rotated, stepwise, every 1°, up to 180°, i.e. 180 images were obtained for the CT construction. Horizontal CT images of several slices of the flower were taken before and after the drying treatment. Vertical CT images of the flower were also constructed based on horizontal CT images. It was found that the water around the ovule was selectively removed by the drying treatment.

3D neutron tomography:: recent developments and first steps towards reverse engineering

The 3D Neutron CT facility at FRM Garching is now operating successfully at a new cold beam line. The higher flux, improved motion control and new image processing software have reduced the time from exposure to 3D model down to one working day. For the first time, reverse engineering techniques have been applied to data generated by neutron CT from metal machine parts. Both 3D models and inverse moulds were created using selective laser sintering, and an exact replica was cast in aluminum.

Correction of scattering neutron effects on neutron CT

Correction of the scattering neutron effects in neutron computed tomography (CT) has been carried out. By subtracting the component of scattering neutrons in CT projection data, only the corrected direct transmitting component through objects is treated. By using the correction of the scattering component on neutron CT, the relatively low contrast on them by neutron electronic imaging method (TV) has been improved. Quantitative analyses with neutron CT have shown a better linear relationship between the neutron macroscopic cross sections and the CT outputs of metal objects.

Improvement of reconstructed image quality in neutron CT : Matsumoto, G.; Sendo, T.; Honda, S.; Ohkubo, K.; Ikeda, Y. neutron radiography, proceedings of the second world conference, Paris (France), 16–20 Jun. 1986. pp. 745–752. D. Reidel Publishing Company

Improvement of reconstructed image quality in neutron CT : Matsumoto, G.; Sendo, T.; Honda, S.; Ohkubo, K.; Ikeda, Y. neutron radiography, proceedings of the second world conference, Paris (France), 16–20 Jun. 1986. pp. 745–752. D. Reidel Publishing Company

中性子ＣＴの改良研究

The images of neutron radiography (NRG) have been able to be digitally analyzed recently. Following it, neutron computed tomography (NCT) attracts people's attention of non-destructive testing field. In our laboratory, the study of NCT technology has been carried out for 5 years. We utilize NRG as a method to obtain projection data. One of the NRG's demerits is to take a long time for measuring film density, and to input it into a computer system. Then, by making use of the image input equipment, instead of micro-densitometer, the data proceeding time is amazingly shortened.This makes it possible to increase the number of projections remarkably. We made an experiment, in which the number of angular projections is 200 (0.9) degree interval, at Kyoto University Reactor (KUR). The quality of obtained CT images is sufficiently good. FWHM of the line spread function for air-stainless steel was 130μm. Resolution power was 400μm for both airstainless steel and aluminum-paraffin. By using image input equipment, it became easy to chase the 3-dimensional shape of an inspected object. We obtained 41 CT images for one object axially at interval of 120-240μm, attempted 3-dimensional reconstruction of the object. Comparing to the real object, the 3-dimensional reconstructed images were satisfactory on shape and dimension.

An application of the neutron television fluoroscopic system to neutron computed tomography

Recently the real-time neutron radiography system of the Kyoto University Reactor (KUR) has been developed and practically applied to penetrating the side plates of the MTR type reactor fuels and investigation of moving objects. In this paper an application of the KUR neutron TV system to neutron computed tomography (NCT) is described. By using the NTV system, projection data can be acquired in a single measurement and simultaneously the projection image can be observed on a CRT monitor. The Fourier-convolution technique is used to produce the reconstructed image and its image has a good enough quality for revealing water in a small hole of 1.5 mm in diameter.

Application of iron-filtered neutrons to radiography of a copper step within a large iron block and to computer tomography of metallic cylinders

A time-of-flight technique and iron-filtered neutrons were applied to neutron radiography and to computer tomography. By making use of iron-filtered neutrons, the existence of 1 mm thick copper within an iron block of 20 cm thickness could be clearly distinguished. To investigate the possibility of neutron computer tomography using iron-filtered neutrons, two cylindrical metallic samples made of CuFePb and CuFeAl were used. From the reconstructed image of the samples, we could clearly see the internal structures.