Marco Röllig^a,⁎, Tsukasa Aso^c, Masanori Hara^b, Florian Priester<sup>a

a</sup> Karlsruhe Institute of Technology, Tritium Laboratory Karlsruhe, P.O. Box 3640, 76021 Karlsruhe, Germany
^b University of Toyama, Hydrogen Isotope research center, Gofuku 3190, Toyama-city, Toyama 930-8555, Japan
^c National Institute of Technology, Toyama College, Ebie-neriya 1-2, Imizu-city, Toyama 933-0293, Japan

Abstract
Four different Geant4 physics packages, Livermore, Penelope, Emstandard Opt4 and Emstandard Opt1, have been benchmarked against real data in the low-energy region ≤18.6 keV, with regard to β-decay induced X-ray spectrometry (BIXS) applications. The tritium data of two different BIXS experiments have been compared against the calculated detection efficiencies and spectral shapes. All four physics package results showed the main features of the experimentally obtained spectra. The spectral shape was reproduced best by the Penelope physics package. Regarding the detection efficiency, the current data set showed the best agreement with Emstandard Opt1 output, while the maximum deviation of ≤24% was given by the Emstandard Opt4 result.

Keywords:BIXS, Beta Induced X-ray Spectrometry,Tritium accountancy,Geant4
Accepted: 13 March 2019

Tsukasa Aso^a*, Masanori Hara^b, Miki Shoji^c, Takayoshi Furusawa^d, Tomoyuki Yoshimura^d and Yuka Kato^d

^aNational Institute of Technology, Toyama College, 1-2 Neriya Ebie, Imizu, Toyama, 933-0293, Japan;
^bHydrogen Isotope Center, Univeristy of Toyama, 3190 Gofuku, Toyama, 930-8555, Japan;
^cLife Science Research Center, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan;
^dHitachi, Ltd., 6-22-1 Mure, Mitaka-shi, Tokyo, 181-8622, Japan

Abstract
Liquid scintillation counter (LSC) is an efficient technique for quantitative measurement of radioactivity in low energy beta decay nuclide. However, the detection efficiency varies with quench effect that caused by missing energy in the conversion from the energy of beta-ray to the intensity of scintillating photons. For the purpose of investigating the effect of photon yield on efficiency and quench level, the Geant4 simulation has been performed. The simulation modeled LSC-5100 manufactured by Hitachi Ltd. It consists of two photomultipliers (PMTs) placed around a sample vial in an optical chamber, and the activity is determined by using the count of double coincidence event in two PMTs. The simulation accounts for radioactive decay, electromagnetic interactions, scintillation and optical photon processes. The LSC spectrum was calculated from optical photons reached at the PMT windows. The photon yields in the simulation were estimated to reproduce the measured spectra in C-14 and H-3 standard quenched samples of Ultima Gold provided by PerkinElmer Co. Ltd. The calculated efficiencies in the photon yields well reproduced the measured efficiencies. In addition, the estimated photon yields were verified in the simulation of the external standard channel ratio (ESCR) with Cs-137 source. The ESCRs in the simulation reproduced the measured ESCRs as well.

Keywords: Geant4 Monte Carlo simulation; liquid scintillation counter; counting efficiency ; H-3;C-14; external standard channel ratio; scintillation photon yield

Satoshi Akamaru^a,⁎, Akihiro Kimura^b , Masanori Hara^a , Katsuhiko Nishimura^b , Takayuki Abe^a

^a Hydrogen Isotope Research Center, Organization for Promotion of Research, 　University of Toyama, Gofuku 3190, Toyama 930-8555, Japan
^b Faculty of Engineering, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan

Abstract
The magnetic properties of Pd–Co alloys and their hydrides were investigated. From the temperature dependences of magnetization of Pd–Co alloys, simple ferromagnetic behaviors were observed, and the Curie temperatures are estimated to be 220, 315, and 350 K for Pd_0.96Co_0.04, Pd_0.92Co_0.08, and Pd_0.90Co_0.10, respectively.The Pd–Co alloys were hydrogenated under 100 kPa hydrogen gas pressure. After hydrogenation, the temperature variations of magnetization revealed two magnetic transitions implying that there are two phases in the hydrogenated Pd–Co: the hydrogen dissolution and hydride phases. The hydrogen contents ([H]/[Pd–Co]) and the Curie temperature (T_C) of the hydride phase are deduced that [H]/[Pd–Co]=0.53, 0.43 and 0.36 with T_C=≤50, 100 and 120 K for Pd_0.96Co_0.04, Pd_0.92Co_0.08, and Pd_0.90Co_0.10 hydrides, respectively. The magnetization against externally applied field measured at 50 and 300 K indicated that the magnetic moments per a single ion (Pd, Co) of the hydrides are always smaller than those of the original Pd–Co alloys. First principle calculations for the magnetic moments provided quite consistent results with the experimental ones.

Keyword:Pd-Co, Hydrogen, Magnetic property, Band structure calculation
Accepted: 29 March 2019

Omar S. Mendoza-Hernandez¹, Asuka Shima¹, Hiroshige Matsumoto², Mitsuhiro Inoue³, Takayuki Abe³, Yoshio Matsuzaki⁴,Yoshitsugu Sone^1,5

¹Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chou-ku, Sagamihara, Kanagawa, 252-5210, Japan.
²International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka,Nishi-ku, Fukuoka City, Fukuoka, 819-0395, Japan.
³Hydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama, 930-8555, Japan.
⁴Fundamental Technology Department, Tokyo Gas. Co., Ltd., 1-7-7 Suehirocho,Tsurumi-ku, Yokohama City, Kanagawa, 230-0045, Japan.
⁵The Graduate University of Advanced Studies, SOKENDAI, 3-1-1 Yoshinodai, Chou-ku, Sagamihara, Kanagawa, 252-5210, Japan.

Abstract
In this work, we introduce a water electrolysis and CO₂ hydrogenation tandem system which focuses on methane generation. The concept consists of a water electrolyzer thermally coupled to a CO₂ hydrogenation reactor, where the power required to generate hydrogen comes from renewable energy.A thermodynamic analysis of the tandem system was carried out. Our analysis exposes that it is possible to increase the exergy efficiency of the water electrolyzer and CO₂ hydrogenation system by thermal coupling, where the thermal energy required to split water into H₂ and O₂ during the electrolysis process is compensated by the heat generated during the CO₂ hydrogenation reaction. Here, the conditions at which high exergy efficiency can be achieved were identified.

Accepted: 27 February 2019

Zhirui Sun,^a,b Ye Tian,^a,b Peipei Zhang,^c Guohui Yang,^c Noritatsu Tsubaki,^c Takayuki Abe,^dAkira Taguchi,^d Jing Zhang,^e Lirong Zheng,^e and Xingang Li,^a,b

^aCollaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P. R. China
^bTianjin Key Laboratory of Applied Catalysis Science and Technology, Tianjin 300072, P. R. China
^cDepartment of Applied Chemistry, School of Engineering, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan
^dHydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan
^eBeijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, P. R. China

Abstract
Dimethyl ether steam reforming (DME SR) is one of attractive technologies to online provide H₂ for fuel cells in vehicles. Herein, we adopt a novel sputtering method to prepare a Cu-ZnO/γ-Al₂O₃ (CuZn−S) bifunctional catalyst with only 2.9 wt % Cu loading. The interaction between Cu and ZnO suppresses the thermal aggregation of Cu nanoparticles in DME SR. The Cu nanoparticles (methanol steam reforming sites) are highly and homogeneously dispersed and anchored on the external surface of γ-Al₂O₃ (DME hydrolysis sites). It significantly improves the utilization efficiency of the Cu species and the mass transfer, thereby achieving high catalytic performance for DME SR. Its reaction rate per unit mass of Cu is 50 times to that of the CuZnAlO/γ-Al₂O₃ catalyst at 300 °C. In addition, this unique structure inhibits the side reactions of methanol direct decomposition and reverse water gas shift to suppress CO production.

Accepted: April 9, 2019

Keisuke Matsubara, Mitsuhiro Inoue, Hidehisa Hagiwara, Takayuki Abe

Hydrogen Isotope Research Center, Organization for Promotion of Research, University of Toyama, 3190 Gofuku, Toyama, 930-8555, Japan

Abstract
Pt-loaded TiO₂ (Pt/TiO₂) catalysts for photocatalytic water splitting were prepared by the polygonal barrelsputtering method. The results showed that the evolution rates of H₂ and O₂ gases for our Pt/TiO₂ catalysts were ca. 5–10 times of those prepared by a conventional photodeposition method. The molar ratios of H₂ versus O₂ were close to be 2, revealing that the stoichiometric water decomposition occurred. The characterizations of the prepared samples implied that the smaller Pt nanoparticles were highly dispersed on the TiO₂ particles by the polygonal barrel-sputtering method. The deposition of the smaller Pt particles increased the Pt surface areas, which can improve the water splitting activities. In addition, the particles deposited by the sputtering method were electron-deficient Pt metals that can enhance the water splitting reaction, whereas those by the photodeposition method were electron-rich Pt metals that reduce the effectiveness of the photocatalytic reaction. These different electron states would play an important role in the remarkable differences in the water splitting activities between the Pt/TiO ₂ catalysts. Consequently, the polygonal barrel-sputtering method is useful for preparing photocatalysts with the high water splitting activities.
Keywords:Photocatalytic water splitting, H₂ production, Pt/TiO₂ photocatalyst, Polygonal barrel-sputtering method Pt nanoparticle

Accepted : 21 April 2019

Kui Ma,^ab Ye Tian,^ab Zhi-Jian Zhao,^ac Qingpeng Cheng,^ab Tong Ding,^ab Jing Zhang,^d Lirong Zheng, ^d Zheng Jiang,^e Takayuki Abe,^f Noritatsu Tsubaki, ^g Jinlong Gong ^*ac and Xingang Li ^*ab

^a School of Chemical Engineering & Technology, Tianjin University, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072,China.
^bTianjin Key Laboratory of Applied Catalysis Science & Engineering, Tianjin 300072, China
^cKey Laboratory for Green Chemical Technology of Ministry of Education, Tianjin 300072, China
^dBeijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
^eShanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics,Chinese Academy of Sciences, Shanghai 201800, China
^fHydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan
^gDepartment of Applied Chemistry, School of Engineering, University of Toyama,Gofuku 3190, Toyama 930-8555, Japan

Abstract

Catalytic reforming provides a practical technique for on-board hydrogen production in fuel cell applications. The high energy density, easy transportation and non-toxicity of biomass-derived dimethylether (bio-DME) offer potential to replace methanol for on-board steam reforming (SR). Presently, the reaction mechanism over conventional Cu-based SR catalysts remains elusive, limiting the rational design of highly efficient reforming systems. Herein, we build a catalytic system for bio-DME SR with dual-sites of Cu species, i.e., Cu⁺ and Cu⁰ sites, and achieve a record-high H₂ production rate of 1145 mol kg_cat ^-1 h^-1. Via regulating the ratios of the dual-sites of Cu, we clearly describe molecular understandings on SR. And we discover that the substantially boosted activity is induced by a new Cu⁺_- determined reaction path substituting the conventional Cu⁰-determined path. Intrinsically, Cu₂O can act as a physical spacer and hydroxyl consumer to suppress the aggregation of metallic Cu species in SR.Due to the unique structure of metallic Cu surrounded by Cu₂O, the catalyst exhibits robust catalytic performance even after severe thermal treatment. These findings open a new avenue for designing efficient catalytic reforming systems with commercial potential.

Accepted: 16th January 2019

Minghui Tan^a,1, Yang Wang ^b,1, Akira Taguchi ^d, Takayuki Abe ^d, Guohui Yang ^a, Mingbo Wu ^c, Noritatsu Tsubaki ^b

^a State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
^b Department of Applied Chemistry, School of Engineering, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan
^c State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, PR China
^d Hydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan

Abstract
A physical sputtering method was adopted to prepare graphene supported highly dispersed and uniform sized Ru NPs without using any solutions, surfactants and reductants. The Ru/G-spu exhibited excellent catalytic performance for HER and hydrolytic dehydrogenation of NaBH₄. Especially for HER in alkaline media, it performed superior electrocatalytic activity over Pt/C. The superior catalytic performance can be attributed to the high exposed surface area and dispersion of Ru NPs on graphene with the open 2D layer structure, which demonstrates the physical sputtering method is a facile and efficient technique to prepare graphene supported metal NPs with excellent structure and catalytic properties.

Keywords:Physical sputtering method, Metal nanoparticles, Graphene H₂ production

Accepted: 27 January 2019

Masao MATSUYAMA, Hideki ZUSHI¹⁾, Kazutoshi TOKUNAGA¹⁾, Arseniy KUZMIN²⁾ and Kazuaki HANADA¹⁾

Hydrogen Isotope Research Center, Organization for Promotion of Research, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan

1)Rearch Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-Koen, Kasuga, Fukuoka 816-8580, Japan

2)National Institute for Fusion Science, Toki, Gifu 509-5292, Japan

Abstract

Effect of the re-deposition layers formed on plasma-exposed stainless steel type 316L (SS316L) in QUEST on the retention and depth profile of tritium has been studied by both methods of tritium exposure experiments and numerical analyses of X-ray spectra observed by the β-ray-induced X-ray spectrometry (BIXS). Both samples of plasma-exposed and non-exposed SS316L were exposed to tritium gas under given temperature, time and pressure conditions. Surface of the former sample was covered with re-deposition layers after exposing to the plasma experiments. After tritium exposure, X-ray spectra induced by β-rays emitted from tritium atoms retained in the surface layers and/or dissolved into the bulk were measured using an ultra-low energy X-ray detector consisting of pure Ge semiconductor, and numerical analysis of the observed spectrum was conducted to estimate a tritium depth profile in the sample. As a result, it was found that the amount of tritium in surface layers of the plasma-exposed sample was about five times larger than that of the non-exposed sample, and the tritium depth profile for the plasma-exposed sample was about half depth in comparison with that for the non-exposed sample although the degassing temperature and tritium exposure conditions were the same for both samples. It was suggested, therefore, that the re-deposition layers played a role of diffusion barrier of tritium atoms formed on the sample surface.

Keywords: tritium retention, tritium depth profile, re-deposition layers, β-ray-induced X-ray spectrum, numerical analysis.
Accepted:4 June 2019

原 正憲，赤丸 悟士, 中山 将人

Abstract
トリチウム管理・測定では，トリチウムに特化した技術が使用されている。これは，トリチウムから放出されるβ線のエネルギーが弱く測定が難しいことに起因する。これら技術がトリチウム施設内での作業環境の維持にどのように使用されているか述べる。最後に，核融合炉ではトリチウムだけでなく，様々な核反応生成物，X線が存在しておりその中でのトリチウムの管理・測定の課題についても述べる。

keywords:作業環境, 電離箱, 液体シンチレーションカウンタ, 空気中濃度限度, スミア法, 内部被ばく

Susumu Fujiwara^1*, Hiroaki Nakamura^2,3, Haolun Li¹, Hisanori Miyanishi³Tomoko Mizuguchi¹, Takuo Yasunaga⁴, Takao Otsuka⁵, Yuji Hatano⁶, Shinji Saito^7
1Faculty of Materials Science and Engineering, Kyoto Institute of Technology
²Department of Helical Plasma Research, National Institute for Fusion Science
³Department of Energy Engineering and Science, Nagoya University
⁴Department of Bioscience and Bioinformatics, Kyushu Institute of Technology
⁵Quantitative Biology Center, RIKEN
⁶Organization for Promotion of Research, University of Toyama
⁷Institute for Molecular Science

Abstract
We propose a computational strategy for investigating structural change of tritiumsubstituted macromolecules. Effects of radiation on macromolecules such as polymeric materials and DNA are classified into three categories: (1) direct action, (2) indirect action, and (3) decay effect. In this study, we focus on the decay effect exclusively. After a beta decay of substituted tritium in macromolecules to helium-3, the generated inert helium-3 is assumed to be deleted quickly. To get an insight into the decay effect to the damage of macromolecules, we perform molecular dynamics simulations of tritium-deleted macromolecules and analyze their structural change. Preliminary simulation results of decay effect on polymeric materials and DNA are presented.

Keywords: Molecular dynamics simulation, Structural change, Macromolecule, Polymeric materials, DNA, Decay effect
Accepted: January 23, 2019

Y. Hatano^a,⁎, S.E. Lee^a, J. Likonen^b, S. Koivuranta^b, M. Hara^a, S. Masuzaki^c, N. Asakura^d, K. Isobe^d, T. Hayashi^d, J. Ikonen^e, A. Widdowson^f, JET contributors^g,1
a University of Toyama, Toyama 930-8555, Japan
^b VTT Technical Research Centre of Finland, P. O. Box 1000, FI-02044 VTT, Finland
^c National Institute for Fusion Science, Toki 509-5292, Japan
^d National Institutes for Quantum and Radiological Science and Technology, Rokkasho 039-3212, Japan
^e University of Helsinki, A. I. Virtasen aukio 1, P. O. Box 55, FI-00014, Finland
^f Culham Centre for Fusion Energy, Culham Science Centre, Abingdon OX14 3DB, UK
^g EUROfusion Consortium, JET, Culham Science Centre, Abingdon OX14 3DB, UK

Abstract
Tritium (T) distributions on tungsten (W)-coated plasma-facing tiles used in the third ITER-like wall campaign (2015–2016) of the Joint European Torus (JET) were examined by means of an imaging plate technique and β- ray induced x-ray spectrometry, and they were compared with the distributions after the second (2013–2014) campaign. Strong enrichment of T in beryllium (Be) deposition layers was observed after the second campaign. In contrast, T distributions after the third campaign was more uniform though Be deposition layers were visually recognized. The one of the possible explanations is enhanced desorption of T from Be deposition layers due to higher tile temperatures caused by higher energy input in the third campaign.

Keywords:Divertor, Tritium, Retention, Deposition, Radiation
Accepted: 1 January 2019

Kazuhito Ohsawa,¹ Takeshi Toyama,² Yuji Hatano,³ Masatake Yamaguchi,⁴ and Hideo Watanabe^1
1Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
²Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan
³Hydrogen Isotope Research Center, Organization for Promotion of Research,University of Toyama, Toyama 930-8555, Japan
⁴Center for Computational Science and e-Systems,Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan

Abstract
Stable structures of hydrogen atoms trapped in a divacancy in tungsten and their binding energies are presented on the basis of first-principle calculations. The hydrogen atoms are favorable sitting in the vicinity of octahedral interstitial sites (O-sites) next to the divacancy. Besides, hydrogen atoms preferentially occupy O-sites located in the center of the divacancy. As hydrogen atoms increases, O-sites located in the periphery of the divacancy are also occupied by the hydrogen atoms. The divacancy in tungsten is energetically unstable, compared with two isolated monovacancies. However, the divacancy is extremely stabilized by the hydrogen atom trapping. The binding energy of the divacancy depends on the sort of the hydrogen isotope.

Accepted : 30 September 2019

Makoto Kobayashi^a,⁎, Masashi Shimada^b, Chase N. Taylor^b, Dean Buchenauer^c,Robert Kolasinski^c, Takaaki Koyanagi^d, Yuji Nobuta^e, Yuji Hatano^f, Yasuhisa Oya^g
a National Institute for Fusion Science, National Institutes of Natural Sciences, 322-6 Oroshi, Toki, Gifu, 509-5202, Japan
^b Idaho National Laboratory, United States
^c Sandia National Laboratory, United States
^d Oak Ridge National Laboratory, United States
^e Hokkaido University, Japan
^f Hydrogen Isotope Research Center, University of Toyama, Toyama, Japan
^g Shizuoka University, Japan

Abstract
Tungsten (W) samples were damaged by neutron and 6.4 MeV Fe-ion irradiation above 1000 K simulating the divertor operation temperature. Deuterium (D) retention properties were examined by decorating the damaged W with D and subsequent thermal desorption spectroscopy (TDS) measurements. Vacancy clusters were the major D trapping site in the W irradiated with Fe-ion at 873 K, although D retention by vacancy clusters decreased in the W irradiated with Fe-ion at 1173 K due to dynamic annealing. The D de-trapping activation energy from vacancy clusters was found to be 1.85 eV. D retention in neutron damage W was larger than that damaged by Fe-ion due to the uniform distribution of irradiation defects. The D desorption behaviors from neutron damaged W was simulated well by assuming the D de-trapping activation energy to be 1.52 eV.

Keywords:Tungsten, Neutron, Divertor, TDS
Accepted: 4 March 2019

Haolun LI, Susumu FUJIWARA, Hiroaki NAKAMURA^1,2), Tomoko MIZUGUCHI, Takuo YASUNAGA³⁾, Takao OTSUKA⁴⁾, Takahiro KENMOTSU⁵⁾, Yuji HATANO⁶⁾ and Shinji SAITO^7)
1)Graduate School of Engineering, Nagoya University, Nagoya 464-8601, Japan
²⁾National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
³⁾Kyushu Institute of Technology, Iizuka 820-8502, Japan
⁴⁾RIKEN, Wako 351-0198, Japan
⁵⁾Doshisha University, Kyotanabe 610-0394, Japan
⁶⁾University of Toyama, Toyama 930-8555, Japan
⁷⁾Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki 444-8585, Japan

Abstract
The molecular mechanism through which how beta decays in tritium-substituted species damage DNA and polymeric materials is still unknown. Molecular dynamics simulations of hydrogen-removed polyethylene were performed to predict the structural change of the polyethylene chain after the substituted tritium decays. We calculated the potential energy, the global orientational order parameter, and the average number of consecutive trans bonds. The results are that, the greater the number of removed hydrogen atoms, the higher the potential energy and the lower the value of the global orientational order parameter and the average number of consecutive trans bonds. Thus, after losing hydrogen, polyethylene becomes poorer in terms of both thermal and structural stabilities.

Keywords: polyethylene, molecular dynamics simulation, beta decay, structural change, tritium
Accepted: 10 April 2019

M. Yajima^a,⁎, Y. Hatano^b, N. Ohno^c, T. Kuwabara^c, T. Toyama^d, M. Takagi^c, K. Suzuki^d
a National Institute for Fusion Science, Oroshi-cho, Toki, 509-5292, Japan
^b Hydrogen Isotope Research Center, Organization for Promotion of Research, Toyama University, Toyama 930-8555, Japan
^c Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8063, Japan
^d Institute for Materials Research, Tohoku University, Oarai-machi, 311-1313, Japan

Abstract
The objective of this study is to investigate the effects of neutron (n) irradiation on hydrogen isotope transport in tungsten (W). W samples were irradiated with neutrons in a fission reactor and then exposed to high flux deuterium (D) plasma at 563 K in a linear plasma device. The fraction of D release increased with increasing exposure time. In addition, the D retention in n-irradiated W increased in proportion to the square root of the plasma exposure time. These observations were explained by increase in the penetration depth of D with filling up displacement damages acting as strong trapping sites.

Accepted: 1 August 2019

N. Ashikawa^a,b*, Y. Torikai^c, N. Asakura^d, T. Otsuka^e, A. Widdowson^f, M. Rubel^g, M. Oyaizu^d, M. Hara^h, S. Masuzaki^a, K. Isobe^d, Y. Hatano^h, K. Heinolaⁱ, A. Baron-Wiechec^f,S. Jachmich^f, T. Hayashi^d
aNational Institute for Fusion Science, Toki, 509-5292 Japan
^bSOKENDAI, Toki, 509-5292 Japan
^cIbaraki University Mito, 310-8512 Japan
^dNational Institute for Quantum and Radiological Science and Technology, Rokkasho, 039-3212 Japan ^eKindai University, Higashi-Osaka, 577-8502, Japan,
^fCCFE, Culham Science Centre, Abingdon, OX14 3DB, UK
^g KTH Royal Institute of Technology, 100 44 Stockholm, Sweden
^hUniversity of Toyama, Toyama, Japan,
ⁱUniversity of Helsinki, Helsinki, Finland

Abstract
Quantitative tritium inventory in dust particles from campaigns in the JET tokamak with the carbon wall (2007-2009) and the ITER-like wall (ILW 2011-2012) were determined by the liquid scintillation counter and the full combustion method. A feature of this full combustion method is that dust particles were covered by a tin (Sn) which reached 2100 K during combustion under oxygen flow. The specific tritium inventory for samples from JET with carbon and with metal walls was measured and found to be similar. However, the total tritium inventory in dust particles from the ILW experiment was significantly smaller in comparison to the carbon wall due to the lower amount of dust particles generated in the presence of metal walls.

Keyword:Dust, JET, ITER-Like Wall, Tritium, liquid scintillography, full combustion method
Accepted: 9 April 2019

Moeko Nakata^a,⁎, Keisuke Azuma^a, Akihiro Togari^a, Qilai Zhou^b, Mingzhong Zhao^c,Takeshi Toyama^d, Yuji Hatano^e, Naoaki Yoshida^f, Hideo Watanabe^f, Masashi Shimada^g,Dean Buchenauer^h, Yasuhisa Oya^a
a Graduate School of Science, Shizuoka University, Shizuoka, 422-8529, Japan
^b Faculty of Science, Shizuoka University, Shizuoka, 422-8529, Japan
^c Graduate School of Science and Technology, Shizuoka University, Shizuoka, 422-8529, Japan
^d Institue for Materials Research, Tohoku University, Ibaraki, 311-1313, Japan
^e Hydrogen Isotope Research Center, University of Toyama, Toyama, 930-8555, Japan
^f Research Institute for Applied Mechanics, Kyushu University, Fukuoka, 816-8580, Japan
^g Fusion Safety Program, Idaho National Laboratory, Idaho Falls, ID, 83415, USA
^h Energy Innovation Department, Sandia National Laboratories, Livermore, CA, 94550, USA

Abstract
0.8 MeV and 6 MeV iron (Fe) ions were implanted into tungsten (W) to produce the irradiation damages with the various damage distributions. Thereafter, 1.0 keV deuterium ion (D₂⁺) implantation was performed to evaluate the D retention behavior on damage distribution in W. The experimental results showed that the total D retentions were decreased by increasing the damage concentration introduced near the surface region by 0.8 MeV Fe ion implantation. The retention of D trapped by vacancy clusters and voids, which would be the stable trapping sites with higher trapping energies, were reduced, suggesting that the recombination of D atom into D₂ on the W surface was enhanced due to D accumulation near the surface region. It can be said that the hydrogen retention behavior in PFMs will be controlled by the damage distribution near the surface.

Keywords:Plasma facing materials, Tungsten, Hydrogen isotope retention behavior, Heavy ion irradiation, Damage distribution
Accepted:19 March 2019

Hidehisa Hagiwara^a, Ittoku Nozawa^a, Katsuaki Hayakawa^a and Tatsumi Ishihara ^bc
aHydrogen Isotope Research Center, Organization for Promotion of Research,University of Toyama
^bInternational Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University
^cDepartment of Applied Chemistry, Faculty of Engineering, Kyushu University

Abstract
Photocatalytic hydrogen production from aqueous hydrogen iodide (HI) over alkali metal tantalates loaded with Pt (Pt/ATaO³, A ¼ Li, Na, or K) was demonstrated. Of the photocatalysts examined, Pt/KTaO³ showed the highest photocatalytic activity for HI decomposition. KTaO³, having the lowest excitation energy, absorbs the largest number of photons for use in photocatalytic reactions, and its corresponding catalyst has the highest number of reaction sites owing to the excellent dispersion of the Pt cocatalyst. These results demonstrate the possibility of developing a new solar-energy-based water splitting process that can convert both light and thermal energy in sunlight to hydrogen energy.

Accepted: 6th August 2019

外山健^a,網恭平^b,佐藤紘一^c,Xu Qiu^d,井上耕治^e，永井康介^e,波多野雄治<sup>f

a</sup>東北大学金属材料研究所,  ^b富山大学大学院理工学教育部
^c鹿児島大学工学部,    ^d京都大学複合原子力科学研究所
^e東北大学金属材料研究所,  ^f富山大学研究推進機構

Abstract
Deuterium trapping at irradiation-induced defects in tungsten, a candidate material for plasma facing components in fusion reactors, was revealed by positron annihilation spectroscopy. Pure tungsten was electron-irradiated (8.5 MeV at ～100℃ and to a dose of ～1 x 10^-3 dpa) or neutron- irradiated (at ～300℃ to a dose of ～0.3 dpa), followed by post-irradiation annealing at 300℃ for 100 hours in deuterium gas at ～0.1 MPa. In both cases of electron- or neutron-irradiation, vacancy clusters were found by positron lifetime measurements. In addition, positron annihilation with deuterium electrons was demonstrated by coincidence Doppler broadening measurements, directly indicating deuterium trapping at vacancy-type defects. This is expected to cause a significant increase in deuterium retention in irradiated-tungsten.

Keywords: defects, tungsten, hydrogen, irradiation
Accepted:2018年10月12日