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Journal Articles

Development of a Gd$$_{2}$$Si$$_{2}$$O$$_{7}$$ (GPS) scintillator-based alpha imaging detector for rapid plutonium detection in high-radon environments

Morishita, Yuki; Izaki, Kenji; Kaneko, Junichi*; Yamamoto, Seiichi*; Higuchi, Mikio*; Torii, Tatsuo

IEEE Transactions on Nuclear Science, 67(10), p.2203 - 2208, 2020/10

 Times Cited Count:4 Percentile:68.2(Engineering, Electrical & Electronic)

We developed a Gd$$_{2}$$Si$$_{2}$$O$$_{7}$$ (GPS) scintillator-based alpha imaging detector and demonstrated its effectiveness by evaluating actual Pu particle and $$^{222}$$Rn progeny. The GPS scintillator plate was prepared by a sintering method. The outer dimensions of the GPS scintillator plate were 5 $$times$$ 5 cm, and the scintillator layer was approximately 50 $$mu$$m on a 3-mm-thick high-transparency glass. The plate was optically coupled to a position-sensitive photomultiplier tube with silicone grease. The developed imaging detector exhibited good uniformity. Pu particle activities were accurately evaluated at 14 different positions, and the difference in activity was within 6%. Radon-222 ($$^{222}$$Rn) progeny counts were reduced by 65.3% by applying an energy window. Although the Pu/$$^{222}$$Rn progeny activity ratio was 1/51, the Pu particle was successfully identified among $$^{222}$$Rn progeny within the 5 min-measurement time. The imaging detector has an excellent ability for detecting Pu among $$^{222}$$Rn progeny. Thus, this detector is useful for alpha contamination monitoring in high-radon-background environments.

Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.

Science, 364(6437), p.272 - 275, 2019/04

 Times Cited Count:170 Percentile:99.77(Multidisciplinary Sciences)

The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

Journal Articles

Optimization of thickness of GAGG scintillator for detecting an alpha particle emitter in a field of high beta and gamma background

Morishita, Yuki; Yamamoto, Seiichi*; Izaki, Kenji; Kaneko, Junichi*; Hoshi, Katsuya; Torii, Tatsuo

Radiation Measurements, 112, p.1 - 5, 2018/05

 Times Cited Count:10 Percentile:81.48(Nuclear Science & Technology)

To detect plutonium isotopes ($$^{238}$$Pu, $$^{239}$$Pu, and $$^{240}$$Pu) in a field of high beta and $$gamma$$ background, an alpha particle detector with low beta and $$gamma$$-ray sensitivity is required. Therefore, we optimized the thickness of the GAGG scintillator for alpha particle detection in a field of high beta and $$gamma$$ background. We prepared three GAGG scintillators with thicknesses of 0.05 mm, 0.07 mm, and 0.1 mm. Each of the GAGG scintillators was coupled optically to the SiPM array, which was used as the photodetector. Alpha, beta, and $$gamma$$ rays were irradiated onto the developed alpha particle detector, and their spectra were obtained. All GAGG scintillators used in this study were not sensitive to $$gamma$$ rays with a dose rate of 1 mSv/h. The beta count of the 0.05-mm-thick GAGG was only 1/100 that of the 0.1-mm-thick GAGG. Therefore, the 0.05-mm-thick GAGG scintillator is promising from the viewpoint of detecting plutonium contamination in a field with high beta and $$gamma$$ background.

Journal Articles

Development of a new detector system to evaluate position and activity of plutonium particles in nasal cavities

Morishita, Yuki; Yamamoto, Seiichi*; Momose, Takumaro; Kaneko, Junichi*; Nemoto, Norio

Radiation Protection Dosimetry, 178(4), p.414 - 421, 2018/03

 Times Cited Count:0 Percentile:0.01(Environmental Sciences)

Plutonium dioxide (PuO$$_{2}$$) is used to fabricate a mixed oxide fuel for fast breeder reactors. When a glove box containing PuO$$_{2}$$ fails, such as by rupture of a glove or a vinyl bag, airborne contamination of plutonium (Pu) can occur. If the worker inhale PuO$$_{2}$$ particles, they deposit in the lung and cause lung cancer. The nasal smear and nose blow methods are useful for checking workers for PuO$$_{2}$$ intake in the field. However, neither method can evaluate the quantitative activity of Pu. No alpha-particle detector that can be used for direct measurements in the nasal cavity has been developed. Therefore, we developed a nasal monitor capable of directly measuring the activity of Pu in the nasal cavity to precisely evaluate the internal exposure dose of a worker. Prismatic-shaped 2$$times$$2 acrylic light guides were used to compose a detector block, and a ZnS(Ag) scintillator was adhered to the surface of these light guides. Silicon photomultiplier (SiPM) arrays with 8$$times$$8 channels were used as a photodetector. Actual PuO$$_{2}$$ particles were measured using the nasal monitor. The nasal monitor could be directly inserted in the nasal cavities. The activity distribution of Pu was obtained by the nasal monitor. The average efficiencies in 4$$pi$$ were 11.43% and 11.58% for the left and right nasal cavities, respectively. The effect of $$gamma$$ and $$beta$$ rays on the detection of the alpha particles of Pu was negligible. The difference in the measured Pu activity between the ZnS(Ag) scintillation counter and the nasal monitor was within 4.0%. The developed nasal monitor can solve the uncertainty problem encountered with the nasal smear and the nose blow methods. We expect this monitor to be useful for accurately estimating the internal exposure dose of workers.

Journal Articles

The Applicability of SiC-SiC fuel cladding to conventional PWR power plant

Furumoto, Kenichiro*; Watanabe, Seiichi*; Yamamoto, Teruhisa*; Teshima, Hideyuki*; Yamashita, Shinichiro; Saito, Hiroaki; Shirasu, Noriko

Proceedings of 2017 Water Reactor Fuel Performance Meeting (WRFPM 2017) (USB Flash Drive), 10 Pages, 2017/09

Since 2015, Mitsubishi Nuclear Fuel (MNF) has joined in a Japanese R&D project of ATF founded by the Ministry of Economy, Trade and Industry (METI) as a subcontractor to Japan Atomic Energy Agency (JAEA) which is the prime contractor to METI. In this program, MNF plans to evaluate an influence of Silicon Carbide (SiC) composite cladding upon fuel rod behavior in current pressurized water reactors (PWR). This paper reports the evaluation result of the applicability of fuel rod with SiC composite cladding for a conventional PWR. For the applicability evaluations of SiC composite to conventional PWR, both of analytical evaluations and out-of-pile tests for SiC composite were conducted. Analytical evaluations were performed by Mitsubishi's own fuel rod design code and the fuel rod behavior evaluation code developed by JAEA. These codes were modified to evaluate the behavior of the fuel rod with SiC composite cladding. As out-of-pile tests, thermal diffusivity measurement and autoclave corrosion test for SiC composite samples were performed. Test apparatus were developed for evaluation of performance of SiC composite under the condition simulated design basis accident (DBA).

Journal Articles

Flexible alpha camera for detecting plutonium contamination

Morishita, Yuki; Yamamoto, Seiichi*; Izaki, Kenji; Kaneko, Junichi*; Nemoto, Norio

Radiation Measurements, 103, p.33 - 38, 2017/08

 Times Cited Count:13 Percentile:83.05(Nuclear Science & Technology)

Nuclear fuel materials, such as uranium and plutonium (Pu), are handled at nuclear fuel facilities. There are a contamination source of Pu in tight spaces that cannot be directly measured by a ZnS(Ag) scintillation detector, such as interspace between a glovebox window and a platform, pipe flange, port cover of vinyl bag, and filter interspaces. Therefore, we developed a new imaging detector called a flexible alpha camera that enables to identify the Pu contamination for tight spaces at work sites. The thickness of the flexible alpha camera was only $$sim$$1/5 of the ZnS(Ag) scintillation detector, and its efficiency for 4-pi direction was 42.7% for 5.5-MeV alpha particles. Minimal detectable activity (MDA) was 0.014 Bq. Four types of PuO$$_{2}$$ sample, removed from a duct, Bag-In/Bag-Out port, glovebox glove, and vinyl sheet, were measured by the flexible alpha camera and the PuO$$_{2}$$ particle was automatically identified. Using the flexible alpha camera, the Pu contamination source can be quickly detected, preventing the spread of contamination.

Journal Articles

Imaging of radiocesium dynamics in soybean by using a high-resolution gamma camera

Yin, Y.-G.; Kawachi, Naoki; Suzui, Nobuo; Ishii, Satomi; Yoshihara, Toshihiro*; Watabe, Hiroshi*; Yamamoto, Seiichi*; Fujimaki, Shu

JAEA-Review 2015-022, JAEA Takasaki Annual Report 2014, P. 112, 2016/02

Journal Articles

Development of a gamma camera system for high-energy gamma photon for quantitative observation of $$^{137}$$Cs movement in a plant body

Kawachi, Naoki; Yin, Y.-G.; Suzui, Nobuo; Ishii, Satomi; Yoshihara, Toshihiro*; Watabe, Hiroshi*; Yamamoto, Seiichi*; Fujimaki, Shu

JAEA-Review 2015-022, JAEA Takasaki Annual Report 2014, P. 94, 2016/02

Journal Articles

Imaging of radiocesium uptake dynamics in a plant body by using a newly developed high-resolution gamma camera

Kawachi, Naoki; Yin, Y.-G.; Suzui, Nobuo; Ishii, Satomi; Yoshihara, Toshihiro*; Watabe, Hiroshi*; Yamamoto, Seiichi*; Fujimaki, Shu

Journal of Environmental Radioactivity, 151(Part 2), p.461 - 467, 2016/01

 Times Cited Count:13 Percentile:47.24(Environmental Sciences)

Journal Articles

Monitoring of positron using high-energy gamma camera for proton therapy

Yamamoto, Seiichi*; Toshito, Toshiyuki*; Komori, Masataka*; Morishita, Yuki*; Okumura, Satoshi*; Yamaguchi, Mitsutaka; Saito, Yuichi; Kawachi, Naoki; Fujimaki, Shu

Annals of Nuclear Medicine, 29(3), p.268 - 275, 2015/04

 Times Cited Count:12 Percentile:54.33(Radiology, Nuclear Medicine & Medical Imaging)

Journal Articles

Ultra-high resolution of radiocesium distribution detection based on Cherenkov light imaging

Yamamoto, Seiichi*; Ogata, Yoshimune*; Kawachi, Naoki; Suzui, Nobuo; Yin, Y.-G.; Fujimaki, Shu

Nuclear Instruments and Methods in Physics Research A, 777, p.102 - 109, 2015/03

 Times Cited Count:3 Percentile:29.72(Instruments & Instrumentation)

Journal Articles

Performance comparison of scintillators for alpha particle detectors

Morishita, Yuki; Yamamoto, Seiichi*; Izaki, Kenji; Kaneko, Junichi*; Toi, Kohei*; Tsubota, Yoichi*; Higuchi, Mikio*

Nuclear Instruments and Methods in Physics Research A, 764, p.383 - 386, 2014/11

 Times Cited Count:27 Percentile:91.7(Instruments & Instrumentation)

Journal Articles

Development of a Si-PM based alpha camera for plutonium detection in nuclear fuel facilities

Morishita, Yuki; Yamamoto, Seiichi*; Izaki, Kenji; Kaneko, Junichi*; Toi, Kohei*; Tsubota, Yoichi*

Nuclear Instruments and Methods in Physics Research A, 747, p.81 - 86, 2014/05

 Times Cited Count:36 Percentile:95.87(Instruments & Instrumentation)

Alpha particles are monitored for detecting nuclear fuel material (i.e., plutonium and uranium) at nuclear fuel facilities. In this study, we developed a new alpha-particle imaging system by combining an Si-PM array, which is insensitive to noise, with a Ce-doped Gd$$_{3}$$Al$$_{2}$$Ga$$_{3}$$O$$_{12}$$ (GAGG) scintillator, and evaluated our developed system's fundamental performance. The scintillator was 0.1-mm thick, and the light guide was 3.0 mm thick. An $$^{241}$$Am source was used for all the measurements. We evaluated the spatial resolution by taking an image of a resolution chart. A 1.6 lp/mm slit was clearly resolved, and the spatial resolution was estimated to be less than 0.6-mm FWHM. The energy resolution was 13% FWHM. A slight distortion was observed in the image, and the uniformity near its center was within 24%. We conclude that our developed alpha-particle imaging system is promising for plutonium detection at nuclear fuel facilities.

Journal Articles

Three-layer GSO depth-of-interaction detector for high-energy gamma camera

Yamamoto, Seiichi*; Watabe, Hiroshi*; Kawachi, Naoki; Fujimaki, Shu; Kato, Katsuhiko*; Hatazawa, Jun*

Nuclear Instruments and Methods in Physics Research A, 743, p.124 - 129, 2014/04

 Times Cited Count:9 Percentile:62.45(Instruments & Instrumentation)

Journal Articles

RI imaging method to analyze a process of radiocesium contamination of plants and to develop phytoremediation techniques

Kawachi, Naoki; Yin, Y.-G.; Suzui, Nobuo; Ishii, Satomi; Watabe, Hiroshi*; Yamamoto, Seiichi*; Fujimaki, Shu

JAEA-Review 2013-059, JAEA Takasaki Annual Report 2012, P. 100, 2014/03

Journal Articles

Isolation of a novel UVB-tolerant rice mutant obtained by exposure to carbon-ion beams

Takano, Nao*; Takahashi, Yuko*; Yamamoto, Mitsuru*; Teranishi, Mika*; Yamaguchi, Hiroko*; Sakamoto, Ayako; Hase, Yoshihiro; Fujisawa, Hiroko*; Wu, J.*; Matsumoto, Takashi*; et al.

Journal of Radiation Research, 54(4), p.637 - 648, 2013/07

 Times Cited Count:11 Percentile:49.11(Biology)

Journal Articles

Tackling contamination of farmland by using NaI(Tl) spectrometer and gamma camera

Yin, Y.-G.; Suzui, Nobuo; Kawachi, Naoki; Yamaguchi, Mitsutaka; Tanoi, Keitaro*; Ishii, Satomi; Nakanishi, Tomoko*; Chino, Mitsuo*; Nakamura, Shinichi*; Watabe, Hiroshi*; et al.

Hoshasen To Sangyo, (133), p.45 - 48, 2012/12

no abstracts in English

Journal Articles

Detailed analyses of key phenomena in core disruptive accidents of sodium-cooled fast reactors by the COMPASS code

Morita, Koji*; Zhang, S.*; Koshizuka, Seiichi*; Tobita, Yoshiharu; Yamano, Hidemasa; Shirakawa, Noriyuki*; Inoue, Fusao*; Yugo, Hiroaki*; Naito, Masanori*; Okada, Hidetoshi*; et al.

Nuclear Engineering and Design, 241(12), p.4672 - 4681, 2011/12

 Times Cited Count:11 Percentile:67.45(Nuclear Science & Technology)

A five-year research project has been initiated in 2005 to develop a code based on the MPS (Moving Particle Semi-implicit) method for detailed analysis of key phenomena in core disruptive accidents (CDAs) of sodium-cooled fast reactors (SFRs). The code is named COMPASS (Computer Code with Moving Particle Semi-implicit for Reactor Safety Analysis). The key phenomena include (1) fuel pin failure and disruption, (2) molten pool boiling, (3) melt freezing and blockage formation, (4) duct wall failure, (5) low-energy disruptive core motion, (6) debris-bed coolability, (7) metal-fuel pin failure. Validation study of COMPASS is progressing for these key phenomena. In this paper, recent COMPASS results of detailed analyses for the several key phenomena are summarized. The present results demonstrate COMPASS will be useful to understand and clarify the key phenomena of CDAs in SFRs in details.

Journal Articles

COMPASS code development; Validation of multi-physics analysis using particle method for core disruptive accidents in sodium-cooled fast reactors

Koshizuka, Seiichi*; Morita, Koji*; Arima, Tatsumi*; Tobita, Yoshiharu; Yamano, Hidemasa; Ito, Takahiro*; Naito, Masanori*; Shirakawa, Noriyuki*; Okada, Hidetoshi*; Uehara, Yasushi*; et al.

Proceedings of 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-8) (CD-ROM), 11 Pages, 2010/10

In this paper, FY2009 results of the COMPASS code development are reported. Validation calculations for melt freezing and blockage formation, eutectic reaction of metal fuel, duct wall failure (thermal-hydraulic analysis), fuel pin failure and disruption and duct wall failure (structural analysis) are shown. Phase diagram calculations, classical and first-principles molecular dynamics were used to investigate physical properties of eutectic reactions: metallic fuel/steel and control rod material/steel. Basic studies for the particle method and SIMMER code calculations supported the COMPASS code development. COMPASS is expected to clarify the basis of experimentally-obtained correlations used in SIMMER. Combination of SIMMER and COMPASS will be useful for safety assessment of CDAs as well as optimization of the core design.

Journal Articles

Detailed analyses of specific phenomena in core disruptive accidents of sodium-cooled fast reactors by the COMPASS code

Morita, Koji*; Zhang, S.*; Arima, Tatsumi*; Koshizuka, Seiichi*; Tobita, Yoshiharu; Yamano, Hidemasa; Ito, Takahiro*; Shirakawa, Noriyuki*; Inoue, Fusao*; Yugo, Hiroaki*; et al.

Proceedings of 18th International Conference on Nuclear Engineering (ICONE-18) (CD-ROM), 9 Pages, 2010/05

A five-year research project has been initiated in 2005 to develop a code based on the MPS (Moving Particle Semi-implicit) method for detailed analysis of specific phenomena in core disruptive accidents (CDAs) of sodium-cooled fast reactors (SFRs). The code is named COMPASS (Computer Code with Moving Particle Semi-implicit for Reactor Safety Analysis). The specific phenomena include (1) fuel pin failure and disruption, (2) molten pool boiling, (3) melt freezing and blockage formation, (4) duct wall failure, (5) low-energy disruptive core motion, (6) debris-bed coolability, and (7) metal-fuel pin failure. Validation study of COMPASS is progressing for these key phenomena. In this paper, recent COMPASS results of detailed analyses for the several specific phenomena are summarized.

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