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Summary of temporal changes in air dose rates and radionuclide deposition densities in the 80 km zone over five years after the Fukushima Nuclear Power Plant accident

斎藤 公明; 三上 智; 安藤 真樹; 松田 規宏; 木名瀬 栄; 津田 修一; 吉田 忠義; 佐藤 哲朗*; 関 暁之; 山本 英明*; et al.

Journal of Environmental Radioactivity, 210, p.105878_1 - 105878_12, 2019/12

 被引用回数:7 パーセンタイル:25.42(Environmental Sciences)

We summarized temporal changes in air dose rates and radionuclide deposition densities over five years in the 80 km zone based on large-scale environmental monitoring data obtained continuously after the Fukushima Nuclear Power Plant (NPP) accident. The air dose rates in environments associated with human lives decreased at a considerably faster rate than expected for radioactive decay. The average air dose rate originating from the radiocesium deposited in the 80 km zone was lower than that predicted from radioactive decay by a factor of 2-3 at five years after the accident. The causes of this rapid reduction were discussed quantitatively considering the characteristics of radiocesium migration in the environment.


Temporal change in radiological environments on land after the Fukushima Daiichi Nuclear Power Plant accident

斎藤 公明; 三上 智; 安藤 真樹; 松田 規宏; 木名瀬 栄; 津田 修一; 佐藤 哲朗*; 関 暁之; 眞田 幸尚; Wainwright-Murakami, Haruko*; et al.

Journal of Radiation Protection and Research, 44(4), p.128 - 148, 2019/12

Massive environmental monitoring has been conducted continuously after the Fukushima accident with different monitoring methods having different features together with migration studies of radiocesium in diverse environments. At three months after the accident, multiple radionuclides were detected at many places; while it was confirmed that radiocesium was most important from the viewpoint of long-term exposures. The air dose rates in environments related to human living have decreased faster than expected from radioactive decay by a factor of 2-3 on average. An empirical model for predicting air dose rate distribution was developed based on statistical analysis of massive car-borne survey data. Some trials were performed to integrate different types of contamination maps to obtain an integrated map of better quantity. Annual external exposure doses for residents who would return to their home were estimated to less than a few mSv as a whole. The environmental data and knowledge have been provided for diverse-spectrum of people in different ways.


Radiation response of silicon carbide metal-oxide-semiconductor transistors in high dose region

大島 武; 横関 貴史; 村田 航一; 松田 拓磨; 三友 啓; 阿部 浩之; 牧野 高紘; 小野田 忍; 土方 泰斗*; 田中 雄季*; et al.

Japanese Journal of Applied Physics, 55(1S), p.01AD01_1 - 01AD01_4, 2016/01

 被引用回数:9 パーセンタイル:42.97(Physics, Applied)

In this study, we report the effects of $$gamma$$-ray irradiation and subsequent annealing on the electrical characteristics of vertical structure power 4H Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) with the blocking voltage of 1200 V. The MOSFETs were irradiated with $$gamma$$-rays up to 1.2 MGy in a N$$_{2}$$ atmosphere at room temperature (RT). During the irradiation, no bias was applied to each electrode of the MOSFETs. After the irradiation, the MOSFETs were kept at RT for 240 h to investigate the stability of their degraded characteristics. Then, the irradiated MOSFETs were annealed up to 360 $$^{circ}$$C in the atmosphere. The current-voltage (I-V) characteristics of the MOSFETs were measured at RT. By 1.2 MGy irradiation, the shift of threshold voltage (V$$_{T}$$) for the MOSFETs was -3.39 V. After RT preservation for 240 h, MOSFETs showed no significant recovery in V$$_{T}$$. By annealing up to 360 $$^{circ}$$C, the MOSFETs showed remarkable recovery, and the values of V$$_{T}$$ become 91 % of the initial values. Those results indicate that the degraded characteristics of SiC MOSFETs can be recovered by thermal annealing at 360 $$^{circ}$$C.


Fabrication of Pt nanoparticle incorporated polymer nanowires by high energy ion and electron beam irradiation

佃 諭志*; 高橋 亮太*; 関 修平*; 杉本 雅樹; 出崎 亮; 吉川 正人; 田中 俊一郎*

Radiation Physics and Chemistry, 118, p.16 - 20, 2016/01

 被引用回数:1 パーセンタイル:82.75(Chemistry, Physical)

ヘキサクロロ白金(IV)酸を添加したポリビニルピロリドン(PVP)薄膜に高エネルギーイオンビームを照射することによってPVP-Ptナノ粒子ハイブリッドナノワイヤを作製した。一個のイオンを照射するとその飛跡に沿って、PVPの架橋反応とPt $$^{4+}$$の還元反応によるPt粒子の析出が同時に起こるため、現像処理後、基板にPtナノ粒子を包含するPVPナノワイヤを得ることができた。ヘキサクロロ白金(IV)酸の添加量を増加するとナノワイヤの直径が減少し、ナノワイヤの単離が困難となることが明らかになったが、イオン照射後、電子線を照射することによってナノワイヤの直径の制御およびナノワイヤの単離が可能であることを見出した。


A Development of super radiation-hardened power electronics using silicon carbide semiconductors; Toward MGy-class radiation resistivity

土方 泰斗*; 三友 啓*; 松田 拓磨*; 村田 航一*; 横関 貴史*; 牧野 高紘; 武山 昭憲; 小野田 忍; 大久保 秀一*; 田中 雄季*; et al.

Proceedings of 11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-11) (Internet), p.130 - 133, 2015/11

In order to develop semiconductor devices with MGy radiation resistivity, we are developing power metal-oxide-semiconductor field-effect-transistors (MOSFETs) based on silicon carbide (SiC) semiconductors. The $$gamma$$-ray irradiation responses of power SiC-MOSFETs were studied under various irradiation temperatures and humidity with various gate-bias conditions. Making comparisons between these responses, the optimum device operating condition and a better device structure were derived and MGy resistivity was achieved. Besides, $$gamma$$-ray irradiation tests for a motor-driver circuits consisting of SiC-MOSFETs were carried out, and as a result, their continuous operation up to 2 MGy was confirmed.


22A beam production of the uniform negative ions in the JT-60 negative ion source

吉田 雅史; 花田 磨砂也; 小島 有志; 柏木 美恵子; Grisham, L. R.*; 畑山 明聖*; 柴田 崇統*; 山本 崇史*; 秋野 昇; 遠藤 安栄; et al.

Fusion Engineering and Design, 96-97, p.616 - 619, 2015/10

 被引用回数:9 パーセンタイル:24.34(Nuclear Science & Technology)



Progress in long-pulse production of powerful negative ion beams for JT-60SA and ITER

小島 有志; 梅田 尚孝; 花田 磨砂也; 吉田 雅史; 柏木 美恵子; 戸張 博之; 渡邊 和弘; 秋野 昇; 小又 将夫; 藻垣 和彦; et al.

Nuclear Fusion, 55(6), p.063006_1 - 063006_9, 2015/06

 被引用回数:28 パーセンタイル:8.03(Physics, Fluids & Plasmas)



福島周辺における空間線量率の測定と評価,4; 環境中における空間線量率測定の実際

津田 修一; 吉田 忠義; 安藤 真樹; 松田 規宏; 三上 智; 谷垣 実*; 奥村 良*; 高宮 幸一*; 佐藤 信浩*; 関 暁之; et al.

Radioisotopes, 64(4), p.275 - 289, 2015/04




秋野 昇; 遠藤 安栄; 花田 磨砂也; 河合 視己人*; 椛澤 稔; 菊池 勝美*; 小島 有志; 小又 将夫; 藻垣 和彦; 根本 修司; et al.

JAEA-Technology 2014-042, 73 Pages, 2015/02




Development of a rapid analytical method for $$^{129}$$I in the contaminated water and tree samples at the Fukushima Daiichi Nuclear Power Station

島田 亜佐子; 小澤 麻由美; 亀尾 裕; 安松 拓洋*; 根橋 宏治*; 新山 拓也; 関 周平; 梶尾 政利; 高橋 邦明

Nuclear Back-end and Transmutation Technology for Waste Disposal, p.311 - 317, 2015/00

汚染水中のI分析におけるIの化学形態と希釈剤の影響を調べるために、3M NaOH溶液とHCl溶液(pH=2)に$$^{129}$$I $$^{-}$$$$^{127}$$IO$$_{3}$$ $$^{-}$$を添加し、還元剤(NaHSO $$_{3}$$)の有無によるIのAnionSRへの吸着ついて調べた。その結果、3M NaOH溶液では還元剤の有無にかかわらず$$^{127}$$Iは抽出されず$$^{129}$$Iは抽出されたことから、3M NaOH溶液中ではI$$^{-}$$は抽出され、IO$$_{3}$$$$^{-}$$は抽出されないこと、還元剤が働かないことが示された。他方、HCl溶液では、$$^{127}$$Iと$$^{129}$$Iが同じ挙動を示し、還元剤なしでは抽出されず、還元剤ありでは抽出されたことから、このHCl溶液中でIは主にIO$$_{3}$$$$^{-}$$として存在し、還元剤によりI$$^{-}$$に還元されたと考えられる。以上によりI$$^{-}$$とIO$$_{3}$$$$^{-}$$を分析するためにはHCl溶液条件が必要であることが分かった。次に、伐採木の分析のために燃焼試験を行った。その結果、100$$^{circ}$$Cから300$$^{circ}$$Cの領域において、段階的にゆっくり昇温することで異常燃焼を避けられること、有機物は酸化剤により分解可能であること、I$$^{-}$$もIO$$_{3}$$$$^{-}$$も約90%がアルカリトラップに回収可能なことを明らかにした。


Fabrication of enzyme-degradable and size-controlled protein nanowires using single particle nano-fabrication technique

大道 正明*; 麻野 敦資*; 佃 諭志*; 高野 勝昌*; 杉本 雅樹; 佐伯 昭紀*; 酒巻 大輔*; 小野田 晃*; 林 高史*; 関 修平*

Nature Communications (Internet), 5, p.3718_1 - 3718_8, 2014/04

 被引用回数:31 パーセンタイル:15.79(Multidisciplinary Sciences)



Current-induced spin polarization on metal surfaces probed by spin-polarized positron beam

Zhang, H.; 山本 春也; 深谷 有喜; 前川 雅樹; Li, H.; 河裾 厚男; 関 剛斎*; 齊藤 英治*; 高梨 弘毅*

Scientific Reports (Internet), 4, p.4844_1 - 4844_5, 2014/04

 被引用回数:30 パーセンタイル:16.91(Multidisciplinary Sciences)

Current-induced spin polarization (CISP) on the outermost surfaces of Au, Cu, Pt, Pd, Ta, and W nanoscaled films were studied using a spin-polarized positron beam. The Au and Cu surfaces showed no significant CISP. In contrast, the Pt, Pd, Ta, and W films exhibited large CISP (3 to 15% per input charge current of 10$$^{5}$$ A/cm$$^{2}$$) and the CISP of Ta and W were opposite to those of Pt and Pd. The sign of the CISP obeys the same rule in spin Hall effect suggesting that the spin-orbit coupling is mainly responsible for the CISP. The magnitude of the CISP is explained by the Rashba-Edelstein mechanism rather than the diffusive spin Hall effect. This settles a controversy, that which of these two mechanisms dominates the large CISP on metal surfaces.


Improvement of uniformity of the negative ion beams by Tent-shaped magnetic field in the JT-60 negative ion source

吉田 雅史; 花田 磨砂也; 小島 有志; 柏木 美恵子; Grisham, L. R.*; 秋野 昇; 遠藤 安栄; 小又 将夫; 藻垣 和彦; 根本 修司; et al.

Review of Scientific Instruments, 85(2), p.02B314_1 - 02B314_4, 2014/02

 被引用回数:10 パーセンタイル:46.48(Instruments & Instrumentation)



化学形に着目した破損燃料からの核分裂生成物及びアクチニドの放出挙動評価; 溶融被覆管と照射済MOX燃料の反応による相状態とFP放出挙動

田中 康介; 三輪 周平; 佐藤 勇; 廣沢 孝志; 関根 伸一; 関 崇行*; 所 大志郎*; 大林 弘; 小山 真一

JAEA-Research 2013-022, 62 Pages, 2014/01




Origin of non-uniformity of the source plasmas in JT-60 negative ion source

吉田 雅史; 花田 磨砂也; 小島 有志; 井上 多加志; 柏木 美恵子; Grisham, L. R.*; 秋野 昇; 遠藤 安栄; 小又 将夫; 藻垣 和彦; et al.

Plasma and Fusion Research (Internet), 8(Sp.1), p.2405146_1 - 2405146_4, 2013/11

本研究では、JT-60負イオン源の端部から引き出される負イオンビームの密度が低い原因を明らかにするために、負イオン源内での負イオン生成の元となる水素イオン及び水素原子の密度分布を静電プローブ及び分光計測にて調べた。またフィラメントから電子の軌道分布を計算コードにて求めた。その結果、負イオンビームの密度が低くなる原因は、電子のB$$times$$grad Bドリフトによって負イオンが非一様に生成されるためであることがわかった。また、負イオンビームが電子数の多い端部では高密度の負イオンを、電子数の少ない反対側の端部では低密度の負イオンを引き出すために歪んでしまい、接地電極に当たっていることも明らかとなった。



津田 修一; 吉田 忠義; 中原 由紀夫; 佐藤 哲朗; 関 暁之; 松田 規宏; 安藤 真樹; 武宮 博; 谷垣 実*; 高宮 幸一*; et al.

JAEA-Technology 2013-037, 54 Pages, 2013/10




Visualization of a single cluster particle track in polystyrene films

麻野 敦資*; 高野 勝昌*; 千葉 敦也; 齋藤 勇一; 丸井 裕美*; 大道 正明*; 前吉 雄太*; 本庄 義人*; 佐伯 昭紀*; 山田 圭介; et al.

JAEA-Review 2012-046, JAEA Takasaki Annual Report 2011, P. 163, 2013/01

In this study, a visualization of the tracks of fragments from a dissociated cluster ion in a target was tried using polystyrene derivatives with higher sensitivity for the ion beam irradiation. The results were compared with the case of ion beam consisting of single ion, considering the feature of cluster beam irradiation. The ion species were selected to be $$^{12}$$C$$_{4}$$$$^{+}$$ and $$^{48}$$Ti$$^{+}$$. As a result, the density of the structures at the $$^{48}$$Ti$$^{+}$$ beam irradiation was almost the same to the ion fluence. However, the density at the $$^{12}$$C$$_{4}$$$$^{+}$$ irradiation was much less than the ion fluence. It is supposed that many cluster particles are fragmentized during penetration in the polymer film. The radial dose distribution inside a particle tracks is decreased, and then the cross-linking reaction is induced insufficiently. In order to visualize the tracks of the fragmentation, optimization of the development or selection of materials with higher sensitivity should be needed.


Visualization of focused proton beam dose distribution by atomic force microscopy using blended polymer films based on polyacrylic acid

大道 正明*; 高野 勝昌*; 佐藤 隆博; 神谷 富裕; 石井 保行; 大久保 猛; 江夏 昌志; 加田 渉; 杉本 雅樹; 西川 宏之*; et al.

Journal of Nanoscience and Nanotechnology, 12, p.7401 - 7404, 2012/09

 被引用回数:2 パーセンタイル:86.35(Chemistry, Multidisciplinary)

A new visualization method for dose distribution of a focused proton beam in sub-micrometer scale was developed using a formation of a bulky cross-linked structure of polyacrylic acid -$$N$$, $$N$$'-methylence bisacrylamide, blend film. The areas irradiated by the focused proton beam were swelled on the film. The height of the swelling was significantly increased according to the beam fluence and the increase of containing ratio of the methylence bisacrylamide. The height was saturated at the fluence of 5$$times$$10$$^5$$ ions/$$mu$$m$$^{2}$$. The proton beam-sensitive polymer film was used for the analysis of dose distribution on its surface. The irradiated surface was observed by employing an atomic force microscope. This observation result showed that the method could be used to confirm the writing patterns and the beam-spot shape. Nanostructures with a crescent shape are visualized clearly at a misaligned beam-spot shape in the set up of the beam-optics.


Fullerene nanowires as a versatile platform for organic electronics

前吉 雄太*; 佐伯 昭紀*; 諏訪 翔太郎*; 大道 正明*; 丸井 裕美*; 麻野 敦資*; 佃 諭志*; 杉本 雅樹; 岸村 顕広*; 片岡 一則*; et al.

Scientific Reports (Internet), 2, p.600_1 - 600_6, 2012/08

 被引用回数:41 パーセンタイル:22.74(Multidisciplinary Sciences)

高分子薄膜に入射するイオンの飛跡に沿って生じる高濃度活性種により直径ナノオーダーの架橋体を形成し、これを溶媒抽出する方法を用いて、フラーレン(C$$_{60}$$)やその誘導体である[6,6]phenyl C$$_{61}$$ butyric acid methyl ester (PC$$_{61}$$BM)のナノワイヤーの作製を試みた。C$$_{60}$$及びPC$$_{61}$$BMを0.1$$sim$$4$$mu$$mの厚さに成膜し、$$^{129}$$Xe$$^{23+}$$ 450MeVあるいは$$^{192}$$Os$$^{30+}$$ 490MeVイオンを照射した結果、半径8$$sim$$11nmのナノワイヤーの作製に成功した。また、有機半導体の原料であるポリチオフェンに、長さ120$$mu$$mのPC$$_{61}$$BMナノワイヤーを数密度1$$times$$10$$^{9}$$cm$$^{-1}$$で混合して試作した有機薄膜太陽電池は、ナノワイヤーを混合しない場合に比べて約7%変換効率が増大することを見いだした。これは、ポリチオフェン中に、PC$$_{61}$$BM分子が個々に分散しているよりも、ナノワイヤーとして混合する方が電子の移動度が大きくなるためと考えられる。微細加工が困難なフラーレン誘導体から、イオンビームを用いた技術によりナノワイヤーが作製可能で有り、これを有機薄膜太陽電池へ応用することで、変換効率が向上できることを実証できた。


Microprocessing of arched bridge structures with epoxy resin by proton beam writing

高野 勝昌*; 麻野 敦資*; 前吉 雄太*; 丸井 裕美*; 大道 正明*; 佐伯 昭紀*; 関 修平*; 佐藤 隆博; 石井 保行; 神谷 富裕; et al.

Journal of Photopolymer Science and Technology, 25(1), p.43 - 46, 2012/07

 被引用回数:2 パーセンタイル:91.41(Polymer Science)

The proton beam writing (PBW) with energy of several MeV ranges is a unique tool of three-dimensional microprocessing for a polymer material. Three-dimensional structures like a bridge structure can be fabricated by the double exposures of PBW with two deferent energies followed by the one-time development using etching solution. In this study, the fabrication of an arched bridge was attempted by means of the supercritical drying with liquid carbon dioxide to a SU-8 photoresist film, as the polymer material, coated on a substrate of epoxy sheet, after the PBW process. In the exposures, two patterns of bridge girders and piers were written with 0.5 and 3 MeV proton beams to the SU-8 photoresist films, respectively. After these writings, the photoresist films were developed with the solution of diacetone alcohol and rinsed with the solution of isopropyl alcohol. Then the supercritical drying with liquid carbon dioxide was used at 12 MPa, 40$$^{circ}$$C. As the results, the bridge structures with curved girders to the vertical direction were formed due to the swelling effect of the photoresist film on the drying. In the conference, the microprocessing method of the bridge structure and the swelling effect of the photoresist film will be represented in detail.

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