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Shimomura, Koichiro*; Koda, Akihiro*; Pant, A. D.*; Sunagawa, Hikaru*; Fujimori, Hiroshi*; Umegaki, Izumi*; Nakamura, Jumpei*; Fujihara, Masayoshi; Tampo, Motonobu*; Kawamura, Naritoshi*; et al.
Interactions (Internet), 245(1), p.31_1 - 31_6, 2024/12
MnShimizu, Kazuyuki*; Nishimura, Katsuhiko*; Matsuda, Kenji*; Akamaru, Satoshi*; Nunomura, Norio*; Namiki, Takahiro*; Tsuchiya, Taiki*; Lee, S.*; Higemoto, Wataru; Tsuru, Tomohito; et al.
Scripta Materialia, 245, p.116051_1 - 116051_6, 2024/05
Times Cited Count：0Hydrogen at the mass ppm level causes hydrogen embrittlement in metallic materials, but it is extremely difficult to experimentally elucidate the hydrogen trapping sites. We have taken advantage of the fact that positive muons can act as light isotopes of hydrogen to study the trapping state of hydrogen in matter. Zero-field muon spin relaxation experiments and the density functional theory (DFT) calculations for hydrogen trapping energy are carried out for AlMn. The DFT calculations for hydrogen in AlMn have found four possible trapping sites in which the hydrogen trapping energies are 0.168 (site 1), 0.312 (site 2), 0.364 (site 3), and 0.495 (site 4) in the unit of eV/atom. Temperature variations of the deduced dipole field width (
) indicated step-like changes at temperatures, 94, 193, and 236 K. Considering their site densities, the observed change temperatures are interpreted by trapping muons at sites 1, 3, and 4.
muon spin relaxation method and first-principles calculationsTsuru, Tomohito; Nishimura, Katsuhiko*; Matsuda, Kenji*; Nunomura, Norio*; Namiki, Takahiro*; Lee, S.*; Higemoto, Wataru; Matsuzaki, Teiichiro*; Yamaguchi, Masatake; Ebihara, Kenichi; et al.
Metallurgical and Materials Transactions A, 54(6), p.2374 - 2383, 2023/06
Times Cited Count：1 Percentile：0(Materials Science, Multidisciplinary)Although hydrogen embrittlement susceptibility of high-strength Al alloys is recognized as a critical issue in the practical use of Al alloys, identifying the hydrogen trapping or distribution has been challenging. In the present study, an effective approach based on experiment and simulation is proposed to explore the potential trap sites in Al alloys. Zero-field muon spin relaxation experiments were carried out for Al-0.5%Mg, Al-0.2%Cu, Al-0.15%Ti, Al-0.011%Ti, Al-0.28%V, and Al-0.015%V (at.%) in the temperature range from 5 to 300 K. The temperature variations of the dipole field widths have revealed three peaks for Al-0.5%Mg, four peaks for Al-0.2%Cu, three peaks for Al-0.011%Ti and Al-0.015%V. Atomic configurations of the muon trapping sites corresponding to the observed peaks are well assigned using the first-principles calculations for the trap energies of hydrogen around a solute and solute-vacancy pair. The extracted linear relationship between the muon peak temperature and the trap energy enables us to explore the potential alloying elements and their complex that have strong binding energies with hydrogen in Al alloys.
Shimomura, Koichiro*; Koda, Akihiro*; Pant, A. D.*; Natori, Hiroaki*; Fujimori, Hiroshi*; Umegaki, Izumi*; Nakamura, Jumpei*; Tampo, Motonobu*; Kawamura, Naritoshi*; Teshima, Natsuki*; et al.
Journal of Physics; Conference Series, 2462, p.012033_1 - 012033_5, 2023/03
Times Cited Count：0 Percentile：0.21(Physics, Applied)Ohshima, Hiroyuki; Morishita, Masaki*; Aizawa, Kosuke; Ando, Masanori; Ashida, Takashi; Chikazawa, Yoshitaka; Doda, Norihiro; Enuma, Yasuhiro; Ezure, Toshiki; Fukano, Yoshitaka; et al.
Sodium-cooled Fast Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.3, 631 Pages, 2022/07
This book is a collection of the past experience of design, construction, and operation of two reactors, the latest knowledge and technology for SFR designs, and the future prospects of SFR development in Japan. It is intended to provide the perspective and the relevant knowledge to enable readers to become more familiar with SFR technology.
Kusano, Kanya*; Ichimoto, Kiyoshi*; Ishii, Mamoru*; Miyoshi, Yoshizumi*; Yoden, Shigeo*; Akiyoshi, Hideharu*; Asai, Ayumi*; Ebihara, Yusuke*; Fujiwara, Hitoshi*; Goto, Tadanori*; et al.
Earth, Planets and Space (Internet), 73(1), p.159_1 - 159_29, 2021/12
Times Cited Count：6 Percentile：49.29(Geosciences, Multidisciplinary)The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.
Hojo, Kiminobu*; Hayashi, Shotaro*; Nishi, Wataru*; Kamaya, Masayuki*; Katsuyama, Jinya; Masaki, Koichi*; Nagai, Masaki*; Okamoto, Toshiki*; Takada, Yasukazu*; Yoshimura, Shinobu*
Mechanical Engineering Journal (Internet), 3(4), p.16-00083_1 - 16-00083_16, 2016/08
Performance demonstration certification of non-destructive inspection for cast stainless steel (CASS) has been planned but the target flaw depth to be detected has not been determined yet in Japan. The target flaw size is closely connected to the allowable flaw size which is determined by flaw evaluation of the rules on fitness-for-service. For rational mitigation of the acceptable flaw size, application of probabilistic fracture mechanics (PFM) is one of the useful countermeasures compared with deterministic approach. In this paper, benchmark problems for a CASS pipe were proposed with intention applying and verifying PFM codes. As the fracture modes, fatigue crack extension, plastic collapse and ductile crack initiation were assumed. Six organizations participated in the benchmark analysis and failure probabilities from them were compared. As a result the failure probability of each problem showed good agreement and the code for application of CASS issue has been verified.
Sasaki, Akira; Nishihara, Katsunobu*; Sunahara, Atsushi*; Nishikawa, Takeshi*
Proceedings of SPIE, Vol.9776, p.97762C_1 - 97762C_6, 2016/03
Times Cited Count：1 Percentile：52.7(Optics)For the improvement of efficiency and output of the laser pumped plasma (LPP) extreme ultra-violet (EUV) light source, we present a hydrodynamics model of laser irradiated Sn targets. The model takes liquid/solid to gas transition and mixed phase condition of the flow into account for the calculation of the distribution of the particles produced by the pre-pulse laser irradiation and optimization of the EUV source. Firstly, we investigate the mechanisms of the fragmentation of the target and particle emission, including the effect of the equation of state of Sn, and secondly, an applicable model is proposed based on the analysis.
Adachi, Taihei*; Ikedo, Yutaka*; Nishiyama, Kusuo*; Yabuuchi, Atsushi*; Nagatomo, Takashi*; Strasser, P.*; Ito, Takashi; Higemoto, Wataru; Kojima, Kenji*; Makimura, Shunsuke*; et al.
JPS Conference Proceedings (Internet), 8, p.036017_1 - 036017_4, 2015/09
Nakatsuji, Satoru*; Kuga, Kentaro*; Kimura, Kenta*; Satake, Ryuta*; Katayama, Naoyuki*; Nishibori, Eiji*; Sawa, Hiroshi*; Ishii, Rieko*; Hagiwara, Masayuki*; Bridges, F.*; et al.
Science, 336(6081), p.559 - 563, 2012/05
Times Cited Count：114 Percentile：95.29(Multidisciplinary Sciences)Frustrated magnetic materials can remain disordered to the lowest temperatures. Such is the case for Ba
CuSb
O
, which is magnetically anisotropic at the atomic scale but curiously isotropic on mesoscopic length and time scales. We find that the frustration on the triangular lattice is imprinted in a nanostructured honeycomb lattice of Cu
ions that resists a coherent static Jahn-Teller distortion. The resulting two-dimensional random-bond spin-1/2 system on the honeycomb lattice has a broad spectrum of spin-dimer like excitations and low-energy spin degrees of freedom that retain.
Sasaki, Akira; Nishihara, Katsunobu*; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishikawa, Takeshi*; Koike, Fumihiro*
Plasma and Fusion Research (Internet), 6(Sp.1), p.2401145_1 - 2401145_4, 2011/12
Atomic processes and radiation from multiple charged ions in plasmas are of the interest in the investigation of plasma wall interaction and transport of impurity ions in the fusion devices. The emission from multiple charged ions is also investigated for the development of extreme ultra violet light (EUVL) sources at 
. Efficient emission through the 4d-4f + 4p-4d transition array is obtained from tin ions. An optimization of pumping conditions of laser produced plasma sources is carried out theoretically and experimentally. We also investigate an extension of the plasma light sources to short wavelength to 
using Gd and Tb plasmas. We discuss requirements to the atomic structure, rate coefficient and collisional radiative codes to determine ion abundance and level population as a function of plasma temperature and density, to calculate the radiation intensity as well as emission spectrum.
Kawamura, Yoshinori; Shu, Wataru*; Matsuyama, Masao*; Yamanishi, Toshihiko
Fusion Science and Technology, 60(3), p.986 - 989, 2011/10
Times Cited Count：4 Percentile：32.48(Nuclear Science & Technology)Assuming the blanket sweep gas at the outlet of the blanket, tritium gas monitor by 
-ray induced X-ray spectroscopy has been modified, and has measured tritium at 120 
C. The counting rate at 120 C was about 1/2 of that at the room temperature. In this work, the measurement system was a closed system. When two systems have same volume and same pressure, the number of molecules in higher temperature system is smaller. This is one of the causes of small counting rate. The deterioration of the scintillator after heating was not observed.
Alimov, V.; Shu, Wataru*; Roth, J.*; Lindig, S.*; Balden, M.*; Isobe, Kanetsugu; Yamanishi, Toshihiko
Journal of Nuclear Materials, 417(1-3), p.572 - 575, 2011/10
Times Cited Count：81 Percentile：98.61(Materials Science, Multidisciplinary)Blistering and deuterium retention in re-crystallized tungsten exposed to a low energy (38 eV/D) and high deuterium ion flux (10
D/m
s) D plasma at ion fluences of 10
and 10
D/m at temperatures in the range from 320 to 800 K have been examined with scanning electron microscopy, thermal desorption spectroscopy (TDS), and the nuclear reaction. During exposure to the D plasma blisters with various shapes and sizes depending on the exposure temperature are formed on the W surface. At the temperatures above 700 K the blisters disappear. The deuterium retention increases with the exposure temperature, reaching its maximum value of about 7
10
D/m at 530 K and about 110 D m at 480 K for ion fluences of 10 and 10 D/m, respectively. As the temperature grows further, the D retention decreases to about 10
D/m at 800 K.
Sasaki, Akira; Nishihara, Katsunobu*; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishikawa, Takeshi*; Koike, Fumihiro*
Applied Physics Letters, 97(23), p.231501_1 - 231501_3, 2010/12
Times Cited Count：15 Percentile：52.55(Physics, Applied)Emission spectrum and conversion efficiency of laser produced terbium plasmas are investigated theoretically on the basis of computational atomic data. It is shown that calculation reproduces the main peak of the experimental spectrum at 
nm, which originates from 4
-4
transitions of near palladium like ions (Tb
). Simple model of the isothermal expansion of plasma suggests that efficient emission can be obtained by pumping a plasma with a laser pulse with an intensity approximately one order of magnitude grater than in the case of tin sources at 
nm.
Sasaki, Akira; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishihara, Katsunobu*; Fujioka, Shinsuke*; Nishikawa, Takeshi*; Koike, Fumihiro*; Ohashi, Hayato*; Tanuma, Hajime*
Journal of Applied Physics, 107(11), p.113303_1 - 113303_11, 2010/06
Times Cited Count：45 Percentile：82.67(Physics, Applied)Atomic processes in Sn plasmas are investigated for application to extreme-ultraviolet (EUV) light sources used in microlithography. An atomic model of Sn is developed on the basis of calculated atomic data using the Hebrew University Lawrence Livermore Atomic Code (HULLAC). Resonance and satellite lines from singly and multiply excited states of Sn ions are identified. The wavelengths of the 4-4 + 4
-4 transitions of Sn
to Sn
are investigated. Results of calculation are compared with those of the charge exchange spectroscopy, measurement of the emission spectrum of the laser produced plasma EUV source, and the opacity measurement of a radiatively heated Sn sample. A reasonable agreement is observed between calculated and experimental EUV emission spectra. The spectral emissivity and opacity of Sn plasmas are calculated using a full collisional radiative (CR) model as a function of electron temperature and ion density.
diffusion in cubic -electron compounds observed by high transverse field SRIto, Takashi; Higemoto, Wataru; Oishi, Kazuki*; Nishida, Nobuhiko*; Heffner, R. H.; Aoki, Yuji*; Suzuki, Hiroyuki*; Onimaru, Takahiro*; Tanida, Hiroshi*; Takagi, Shigeru*
Journal of Physics; Conference Series, 225, p.012021_1 - 012021_6, 2010/06
Times Cited Count：2 Percentile：66.79(Physics, Applied)The diffusion of positive muon in condensed matter has been investigated for many years by using spin rotation/relaxation (SR) technique. The SR studies have provided deep insight into quantum diffusion at low temperatures as well as hopping process at high temperatures, which are closely related to hydrogen dynamics in the dilute limit. We here report transverse field (TF) SR studies of the diffusion in cubic -electron compounds PrPb and SmAgIn. The site splits into two magnetically labeled sites when high TF is applied to single-crystalline specimens along the [001] direction. The SR lines show drastic variation according to the motion between the magnetically labeled sites. From detailed analysis of the SR lines, we deduced hopping parameters for both compounds.
Miyake, Yasuhiro*; Shimomura, Koichiro*; Kawamura, Naritoshi*; Strasser, P.*; Makimura, Shunsuke*; Koda, Akihiro*; Fujimori, Hiroshi*; Nakahara, Kazutaka*; Takeshita, Soshi*; Kobayashi, Yasuo*; et al.
Journal of Physics; Conference Series, 225, p.012036_1 - 012036_7, 2010/06
Times Cited Count：9 Percentile：92.69(Physics, Applied)Strasser, P.*; Shimomura, Koichiro*; Koda, Akihiro*; Kawamura, Naritoshi*; Fujimori, Hiroshi*; Makimura, Shunsuke*; Kobayashi, Yasuo*; Nakahara, Kazutaka*; Kato, Mineo*; Takeshita, Soshi*; et al.
Journal of Physics; Conference Series, 225, p.012050_1 - 012050_8, 2010/06
Times Cited Count：12 Percentile：95.19(Physics, Applied)Higemoto, Wataru; Ito, Takashi; Ninomiya, Kazuhiko; Heffner, R.*; Shimomura, Koichiro*; Nishiyama, Kusuo*; Miyake, Yasuhiro*
Journal of Physics; Conference Series, 225, p.012012_1 - 012012_4, 2010/06
Times Cited Count：2 Percentile：66.79(Physics, Applied)The Japan Atomic Energy Agency (JAEA)-Advanced Science Research Center (ASRC) has developed experimental equipment at the J-PARC MLF muon science facility (MUSE) for muon spin rotation/relaxation experiments. We have extracted part of the muonbeam into a muon spectrometer constructed downstream from the Decay/Surface muon beam line. The current status of our project is discussed here.
Al
by SRKambe, Shinsaku; Chudo, Hiroyuki; Tokunaga, Yo; Koyama, Takehide*; Sakai, Hironori; Ito, Takashi; Ninomiya, Kazuhiko; Higemoto, Wataru; Takesaka, Tomoaki*; Nishioka, Takashi*; et al.
Journal of the Physical Society of Japan, 79(5), p.053708_1 - 053708_3, 2010/05
Times Cited Count：53 Percentile：86.86(Physics, Multidisciplinary)We report zero-field 
SR measurements made at J-PARC on CeRuAl. Below the phase transition temperature 
K, a clear modulation of polarization due to an internal field is observed, indicating that magnetic ordering takes place. Compared with the internal field expected from the effective magnetic moment in the disordered state, the observed internal field at the site is quite small. This indicates that the ordered Ce magnetic moment is small (
) and/or the nearest pair of Ce magnetic moments are mutually anti-parallel. The 
-dependence of the internal field is somewhat peculiar, suggesting that another ordering is taking place as well.
