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Mikami, Satoshi; Tanaka, Hiroyuki*; Okuda, Naotoshi*; Sakamoto, Ryuichi*; Ochi, Kotaro; Uno, Kiichiro*; Matsuda, Norihiro; Saito, Kimiaki
Nihon Genshiryoku Gakkai Wabun Rombunshi, 20(4), p.159 - 178, 2021/12
In order to know the background radiation level where the area affected by the Fukushima Daiichi Nuclear Power Plant accident in 2011, terrestrial gamma rays had been measured by using portable germanium detectors repeatedly from 2013 through 2019, at 370 locations within 80 km radius area centered on the Fukushima Daiichi Nuclear Power Plant. Radioactive concentrations of Uranium 238, Thorium 232, Potassium 40 and kerma rates in air due to terrestrial gamma rays were obtained at those locations based on the method of ICRU report 53. Averaged concentrations of U, Th and K were 18.8, 22.7, 428 Bq/kg, respectively, and kerma rate in air over the area was found to be 0.0402 Gy/h. The obtained kerma rates in air were compared to those reported in literatures. It was confirmed that the data were correlated with each other, and were agreed within the range of their uncertainty. This is because the kerma rate in air due to terrestrial gamma rays is depend on geology. The similar trend to previous findings was observed that the kerma rate in air at locations geologically classified as Mesozoic era, Granite and Rhyolite were statistically significantly higher than the others.
Mikami, Satoshi; Tanaka, Hiroyuki*; Matsuda, Hideo*; Sato, Shoji*; Hoshide, Yoshifumi*; Okuda, Naotoshi*; Suzuki, Takeo*; Sakamoto, Ryuichi*; Ando, Masaki; Saito, Kimiaki
Journal of Environmental Radioactivity, 210, p.105941_1 - 105941_12, 2019/12
Times Cited Count:20 Percentile:67.75(Environmental Sciences)The deposition densities of radiocesium and the air dose rates were repeatedly measured in a large number of undisturbed fields within the 80km zone that surrounds the Fukushima Dai-ichi Nuclear Power Plant site between 2011 and 2016, and features of their temporal changes were clarified. The average air dose rate excluding background radiation in this zone decreased to about 20% of the initial value during the period from June 2011 to August 2016, which was essentially a result of the radioactive decay of Cs with a half-life of 2.06y. The air dose rate reduction was faster than that expected from the decay of radiocesium by a factor of about two, with most of this reduction being attributed to the penetration of radiocesium into the soil. The average deposition densities of Cs and Cs in fields that were not decontaminated were found to have decreased nearly according to their expected radioactive decay, which indicated that the movement of radiocesium in the horizontal direction was relatively small. The effect of decontamination was apparently observed in the measurements of air dose rates and deposition densities. Nominally, the average air dose rates in the measurement locations were reduced by about 20% by decontamination and other human activities, of which accurate quantitative analysis is and continue to be a challenge.
Ida, Katsumi*; Sakamoto, Yoshiteru; Inagaki, Shigeru*; Takenaga, Hidenobu; Isayama, Akihiko; Matsunaga, Go; Sakamoto, Ryuichi*; Tanaka, Kenji*; Ide, Shunsuke; Fujita, Takaaki; et al.
Nuclear Fusion, 49(1), p.015005_1 - 015005_7, 2009/01
Times Cited Count:13 Percentile:45.19(Physics, Fluids & Plasmas)Transport analysis during the transient phase of heating (a dynamic transport study) applied to the plasma with internal transport barriers (ITBs) in the Large Helical Device (LHD) heliotron and the JT-60U tokamak is described. In the dynamic transport study the time of transition from the L-mode plasma to the ITB plasma is clearly determined by the onset of flattening of the temperature profile in the core region and a spontaneous phase transition from a zero curvature ITB (hyperbolic tangent shaped ITB) or a positive curvature ITB (concaved shaped ITB) to a negative curvature ITB (convex shaped ITB) and its back-transition are observed. The flattening of the core region of the ITB transition and the back-transition between a zero curvature ITB and a convex ITB suggest the strong interaction of turbulent transport in space.
Saito, Shinzo*; Tanaka, Ryuichi*; Kume, Tamikazu; Inoue, Tomio*; Takahashi, Shoji*
Genshiryoku eye, 54(5), p.34 - 41, 2008/05
no abstracts in English
Ninomiya, Hiromasa; Akiba, Masato; Fujii, Tsuneyuki; Fujita, Takaaki; Fujiwara, Masami*; Hamamatsu, Kiyotaka; Hayashi, Nobuhiko; Hosogane, Nobuyuki; Ikeda, Yoshitaka; Inoue, Nobuyuki; et al.
Journal of the Korean Physical Society, 49, p.S428 - S432, 2006/12
To contribute DEMO and ITER, the design to modify the present JT-60U into superconducting coil machine, named National Centralized Tokamak (NCT), is being progressed under nationwide collaborations in Japan. Mission, design and strategy of this NCT program is summarized.
Kikuchi, Mitsuru; Tamai, Hiroshi; Matsukawa, Makoto; Fujita, Takaaki; Takase, Yuichi*; Sakurai, Shinji; Kizu, Kaname; Tsuchiya, Katsuhiko; Kurita, Genichi; Morioka, Atsuhiko; et al.
Nuclear Fusion, 46(3), p.S29 - S38, 2006/03
Times Cited Count:13 Percentile:41.84(Physics, Fluids & Plasmas)The National Centralized Tokamak (NCT) facility program is a domestic research program for advanced tokamak research to succeed JT-60U incorporating Japanese university accomplishments. The mission of NCT is to establish high beta steady-state operation for DEMO and to contribute to ITER. The machine flexibility and mobility is pursued in aspect ratio and shape controllability, feedback control of resistive wall modes, wide current and pressure profile control capability for the demonstration of the high-b steady state.
Tsuchiya, Katsuhiko; Akiba, Masato; Azechi, Hiroshi*; Fujii, Tsuneyuki; Fujita, Takaaki; Fujiwara, Masami*; Hamamatsu, Kiyotaka; Hashizume, Hidetoshi*; Hayashi, Nobuhiko; Horiike, Hiroshi*; et al.
Fusion Engineering and Design, 81(8-14), p.1599 - 1605, 2006/02
Times Cited Count:1 Percentile:9.98(Nuclear Science & Technology)no abstracts in English
Tamai, Hiroshi; Akiba, Masato; Azechi, Hiroshi*; Fujita, Takaaki; Hamamatsu, Kiyotaka; Hashizume, Hidetoshi*; Hayashi, Nobuhiko; Horiike, Hiroshi*; Hosogane, Nobuyuki; Ichimura, Makoto*; et al.
Nuclear Fusion, 45(12), p.1676 - 1683, 2005/12
Times Cited Count:15 Percentile:45.55(Physics, Fluids & Plasmas)Design studies are shown on the National Centralized Tokamak facility. The machine design is carried out to investigate the capability for the flexibility in aspect ratio and shape controllability for the demonstration of the high-beta steady state operation with nation-wide collaboration, in parallel with ITER towards DEMO. Two designs are proposed and assessed with respect to the physics requirements such as confinement, stability, current drive, divertor, and energetic particle confinement. The operation range in the aspect ratio and the plasma shape is widely enhanced in consistent with the sufficient divertor pumping. Evaluations of the plasma performance towards the determination of machine design are presented.
Takenaga, Hidenobu; Oyama, Naoyuki; Fujita, Takaaki; Yamada, Hiroshi*; Nishimura, Kiyohiko*; Tanaka, Kenji*; Sakamoto, Ryuichi*
Annual Report of National Institute for Fusion Science; April 2003 - March 2004, P. 12, 2003/10
no abstracts in English
Tanaka, Osamu*; Akiyama, Fumiaki*; Yamada, Akihisa*; Ando, Sada*; Uegaki, Ryuichi*; Kobayashi, Ryoei*; Kume, Tamikazu
Nihon Sochi Gakkai-Shi, 47(3), p.274 - 282, 2001/08
no abstracts in English
Ishii, Yasuyuki; Isoya, Akira*; Arakawa, Kazuo; Kojima, Takuji; Tanaka, Ryuichi*
Nuclear Instruments and Methods in Physics Research B, 181(1-4), p.71 - 77, 2001/07
Times Cited Count:13 Percentile:69.02(Instruments & Instrumentation)no abstracts in English
Kojima, Takuji; Tachibana, Hiroyuki; Haneda, Noriyuki; Kaneko, Hirohisa; Haruyama, Yasuyuki; Tanaka, Ryuichi*
Radioisotopes, 50(7), p.291 - 300, 2001/07
Plaque type Co -ray sources having wide radiation field with high absorbed dose rates ranging of about 10010,000Gy/h is widely used in radiation processing e.g. radiation sterilization of health care products. Calibration of such radiation processing doses or dose rates is not easy to be performed at the present standard dosimetry laboratories, since characteristics of most of their radiation field can provide collimated gamma-rays from a point source and/or lower dose rates, which are quite different from those of panoramic (uncollimated) radiation fields used in radiation processing. The high-dose calibration technique using a parallel-plate ionization chamber system has developed in the JAERI dose calibration facility. The facility equips two Co -ray plaque sources covering wide dose-rate range of 520,000 Gy/h which have overlapping dose-rate region with that at the National Institute of Advanced Industrial Science and Technology(AIST), the national standard Dosimetry laboratory in Japan. Consistency of dose calibration results at JAERI and those at AIST was verified without additional correction regarding to difference in characteristics of radiation fields involving current/exposure -rate conversion coefficients given in the dose rate level of 10100 Gy/h at the AIST and high-dose rates of 520,000 Gy/h at JAERI. It demonstrates our dose traceability to the AIST from the technical point of view. The dose calibration at JAERI covers the high-dose range of 0.5 to Gy with uncertainty of 2.2% at 95% confidence level.
Tanaka, Osamu*; Akiyama, Fumiaki*; Yamada, Akihisa*; Ando, Sada*; Uegaki, Ryuichi*; Kobayashi, Ryoei*; Kume, Tamikazu
Nihon Sochi Gakkai-Shi, 47(1), p.62 - 67, 2001/04
no abstracts in English
Ishii, Yasuyuki; Isoya, Akira*; Arakawa, Kazuo; Tanaka, Ryuichi*
JAERI-Conf 2000-019, p.117 - 120, 2001/02
no abstracts in English
Tanaka, Ryuichi*
Genshiryoku Shisutemu Nyusu, 11(1), p.14 - 20, 2000/06
no abstracts in English
Kojima, Takuji; Sunaga, Hiromi; Tachibana, Hiroyuki; Takizawa, Haruki; Tanaka, Ryuichi
IAEA-TECDOC-156, p.91 - 98, 2000/06
no abstracts in English
Sunaga, Hiromi; *; *; Takizawa, Haruki; Yotsumoto, Keiichi; *; Tanaka, Ryuichi; *
JAERI-Tech 99-046, 63 Pages, 1999/06
no abstracts in English
Tachibana, Hiroyuki; Kojima, Takuji; ; ; Yotsumoto, Keiichi; Tanaka, Ryuichi
Radioisotopes, 48(4), p.247 - 256, 1999/04
no abstracts in English
Tanaka, Ryuichi*; Yanagisawa, Kazuaki
Hoshasen Kyoiku, 3(1), p.51 - 57, 1999/00
no abstracts in English
Saido, Masahiro; Fukuda, Mitsuhiro; Arakawa, Kazuo; Tajima, Satoshi; Sunaga, Hiromi; Yotsumoto, Keiichi; Kamiya, Tomihiro; Tanaka, Ryuichi; Hirao, Toshio; Nashiyama, Isamu; et al.
Proceedings of 1999 IEEE Nuclear and Space Radiation Effects Conference, p.117 - 122, 1999/00
no abstracts in English