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Abstract: A device for evaluating the spatial resolution of a neutron imaging system was developed. Using laser processes, line- pair patterns were fabricated on a 0.005-mm-thick Gd film evaporated on a glass plate. Large line pairs of widths ranging from 0.2 to 2mm were machined using an Nd:YVO4 laser (0.03mm spot size) and displayed on a brightness field, while small line pairs of widths ranging from 0.01 to 0.1mm were created using an eximer laser on a dark field. A scanning electron microscope (SEM) observation determined that, although the large line pairs machined using the Nd:YVO4 laser were chipped on the corners of the Gd bars, the difference between the measured and designed line- pair widths was controlled absolutely within 0.02mm. In the small line pairs of less than 0.1mm width processed using the eximer laser, edges sharper than those of the large line pairs were formed. In neutron imaging tests using a LiF/ZnS(Ag) scintillator and a CCD camera system, good contrast images were obtained with the brightness field, even at 0.005mm thickness. The small line pairs on the dark field were observed using a LiF single crystal detector having an ultra-high spatial resolution of approximately 0.005mm. Splits in the small line pairs of as little as 0.01mm wide were shown with good contrast on the images. [Copyright &y& Elsevier]

Abstract: In neutron imaging, enhancing the brightness of a neutron detector is an important factor for shortening the imaging time and improving the image quality. Recently, we devised a technique for increasing the light intensity received on a camera by adding brightness enhancement films (BEFs) on the output surface of a scintillator. Using a BEF (BEF II 90/24, Vikuiti 3M), the brightness was enhanced, but the spatial resolution was reduced. In this study, we investigated the brightness and spatial resolution using several types of BEFs with different thicknesses and prism pitches. No correlation between the brightness and the film thickness, and between the brightness and the prism pitch, was recognized. For the spatial resolution, however, when the film thickness was reduced, the spatial resolution was observed to improve. [Copyright &y& Elsevier]

Abstract: Japan Atomic Energy Agency has developed the neutron scintillator jointly with Chichibu Fuji Co., Ltd. In this study, we evaluated the new ZnS(Ag):Al/6Li scintillator developed for neutron imaging. It was confirmed that the brightness increased by about double while maintaining equal performance for the spatial resolution as compared with a conventional scintillator. High frame-rate imaging using a high-speed video camera system and this new scintillator made it possible to image beyond 10000 frames per second while still having enough brightness. This technique allowed us to obtain a high-frame-rate visualization of oil flow in a running car engine. Furthermore, we devised a technique to increase the light intensity of reception for a camera by adding brightness enhancement films on the output surface of the scintillator. It was confirmed that the spatial resolution degraded more than double, but the brightness increased by about three times. [Copyright &y& Elsevier]

Abstract: Neutron radiography is one of the useful tools for visualizing water behavior in operating fuel cells. In order to observe the detailed information about the water distribution in membrane electrode assembly (MEA) and gas diffusion layer (GDL) in fuel cells, a high performance neutron imaging system is required. A neutron color image intensifier (NCII) is a high spatial resolution and high sensitivity neutron image detector. We have developed an imaging system using an NCII for visualizing the behavior of water in fuel cells. The pixel size of the imaging system is around 4.7μm in the small view field. By using this system, water distribution of a small sized fuel cell was observed continuously every 20s at the Thermal Neutron Radiography Facility (TNRF). In the results, the water area appears from the GDL and MEA regions, and expanded to the cathode side channel with time. However, the voltage was gradually reduced with time, and steeply dropped. It is considered that the reduction and the drop of voltage were caused by a blockage of gas flow due to accumulation of water in the GDL and the gas flow channel in the cathode side. [Copyright &y& Elsevier]

Abstract: Neutron imaging by color center formation in LiF crystals was applied to a sensitivity indicator (SI) as a standard samples for neutron radiography. The SI was exposed to a 5mm pinhole-collimated thermal neutron beam with an LiF crystal and a neutron imaging plate (NIP) for 120min in the JRR-3M thermal neutron radiography facility. The image in the LiF crystal was read out using a laser confocal microscope. All gaps were clearly observed in images for both the LiF crystal and the NIP. The experimental results showed that LiF crystals have excellent characteristics as neutron imaging detectors in areas such as high spatial resolution. [Copyright &y& Elsevier]

Abstract: A multi-pinhole collimator system, which is effective for enlarging imaging area with high spatial resolution, has been demonstrated on Cold Neutron Radiograph Facility at JRR-3M in JAEA. The multi-pinhole collimator system consists of a multi-pinhole aperture and an overlap-cutter. On neutron beam from the multi-pinhole aperture, neutrons from each pinhole overlap at the sample position due to beam divergence. In the overlap area, sample images from each pinhole are obtained at a detector and these images look like split images. The overlap-cutter works to cut neutrons contribute to overlap at sample position and enable us to get an image without split. Imaging area was enlarged and sharp image without split was successfully obtained by using the multi-pinhole collimator system. [Copyright &y& Elsevier]