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OKondo, Yosuke*; Achouri, N. L.*; Al Falou, H.*; Atar, L.*; Aumann, T.*; Baba, Hidetada*; Boretzky, K.*; Caesar, C.*; Calvet, D.*; Chae, H.*; et al.
Nature, 620(7976), p.965 - 970, 2023/08
Times Cited Count：6 Percentile：93.26(Multidisciplinary Sciences)no abstracts in English
Ne at the transition into the island of inversion; Detailed structure study of NeWang, H.*; Yasuda, Masahiro*; Kondo, Yosuke*; Nakamura, Takashi*; Tostevin, J. A.*; Ogata, Kazuyuki*; Otsuka, Takaharu*; Poves, A.*; Shimizu, Noritaka*; Yoshida, Kazuki; et al.
Physics Letters B, 843, p.138038_1 - 138038_9, 2023/08
Times Cited Count：2 Percentile：83.53(Astronomy & Astrophysics)Detailed 
-ray spectroscopy of the exotic neon isotope Ne has been performed using the one-neutron removal reaction from Ne. Based on an analysis of parallel momentum distributions, a level scheme with spin-parity assignments has been constructed for Ne and the negative-parity states are identified for the first time. The measured partial cross sections and momentum distributions reveal a significant intruder p-wave strength providing evidence of the breakdown of the N = 20 and N = 28 shell gaps. Only a weak, possible f-wave strength was observed to bound final states. Large-scale shell-model calculations with different effective interactions do not reproduce the large p-wave and small f-wave strength observed experimentally, indicating an ongoing challenge for a complete theoretical description of the transition into the island of inversion along the Ne isotopic chain.
Koyama, Shinichi; Nakagiri, Toshio; Osaka, Masahiko; Yoshida, Hiroyuki; Kurata, Masaki; Ikeuchi, Hirotomo; Maeda, Koji; Sasaki, Shinji; Onishi, Takashi; Takano, Masahide; et al.
Hairo, Osensui Taisaku jigyo jimukyoku Homu Peji (Internet), 144 Pages, 2021/08
JAEA performed the subsidy program for the "Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris (Development of Technologies for Enhanced Analysis Accuracy and Thermal Behavior Estimation of Fuel Debris))" in 2020JFY. This presentation summarized briefly the results of the project, which will be available shortly on the website of Management Office for the Project of Decommissioning and Contaminated Water Management.
-Orbital component in the Borromean nucleus 
BYang, Z. H.*; Kubota, Yuki*; Corsi, A.*; Yoshida, Kazuki; Sun, X.-X.*; Li, J. G.*; Kimura, Masaaki*; Michel, N.*; Ogata, Kazuyuki*; Yuan, C. X.*; et al.
Physical Review Letters, 126(8), p.082501_1 - 082501_8, 2021/02
Times Cited Count：45 Percentile：96.69(Physics, Multidisciplinary)A quasifree (
,
) experiment was performed to study the structure of the Borromean nucleus B, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for 
and 
orbitals, and a surprisingly small percentage of 9(2)% was determined for . Our finding of such a small component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in B. The present work gives the smallest - or -orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of or orbitals is not a prerequisite for the occurrence of a neutron halo.
Wang, H.*; Otsu, Hideaki*; Chiga, Nobuyuki*; Kawase, Shoichiro*; Takeuchi, Satoshi*; Sumikama, Toshiyuki*; Koyama, Shumpei*; Sakurai, Hiroyoshi*; Watanabe, Yukinobu*; Nakayama, Shinsuke; et al.
Communications Physics (Internet), 2(1), p.78_1 - 78_6, 2019/07
Times Cited Count：8 Percentile：55.71(Physics, Multidisciplinary)Searching for effective pathways for the production of proton- and neutron-rich isotopes through an optimal combination of reaction mechanism and energy is one of the main driving forces behind experimental and theoretical nuclear reaction studies as well as for practical applications in nuclear transmutation of radioactive waste. We report on a study on incomplete fusion induced by deuteron, which contains one proton and one neutron with a weak binding energy and is easily broken up. This reaction study was achieved by measuring directly the cross sections for both proton and deuteron for 
Pd at 50 MeV/u via inverse kinematics technique. The results provide direct experimental evidence for the onset of a cross-section enhancement at high energy, indicating the potential of incomplete fusion induced by loosely-bound nuclei for creating proton-rich isotopes and nuclear transmutation of radioactive waste.
Si revealed by comparison with nonmagnetic references ThRuSi and LaRuSiEmi, Naoya*; Hamabata, Ryosuke*; Nakayama, Daisuke*; Miki, Toshihiro*; Koyama, Takehide*; Ueda, Koichi*; Mito, Takeshi*; Kohori, Yo*; Matsumoto, Yuji*; Haga, Yoshinori; et al.
Journal of the Physical Society of Japan, 84(6), p.063702_1 - 063702_4, 2015/06
Times Cited Count：10 Percentile：58.29(Physics, Multidisciplinary)Tanno, Takashi; Otsuka, Satoshi; Yano, Yasuhide; Kaito, Takeji; Oba, Yojiro*; Onuma, Masato*; Koyama, Shinichi; Tanaka, Kenya
Journal of Nuclear Materials, 440(1-3), p.568 - 574, 2013/09
Times Cited Count：17 Percentile：78.02(Materials Science, Multidisciplinary)This study carried out mechanical tests and microstructure characterizations of several 9Cr and 11Cr-ODS tempered martensitic steels, and discussed the appropriate chemical composition range of 11Cr-ODS tempered martensitic steel from the viewpoint of high-temperature strength improvement. It was shown that the residual 
-ferrite fraction in 11Cr-ODS steel was successfully controlled to the same level as the 9Cr-ODS steel by selecting the matrix chemical compositions on the basis of the multi-component phase diagram. The tensile strength decreased with decreasing W content from 2.0 to 1.4 wt%. On the other hand, creep strength at 973 K did not degrade by the decreasing W content. Both tensile strength and creep strength increased with increasing population of the nano-sized oxide particles. Small angle X-ray scattering analysis revealed that titanium and excess oxygen contents were key parameters in order to improve the dispersion condition of nano-sized oxide particles.
Am content on homogenization of denatured Pu with broad range of neutron energy based on U irradiation test in the experimental fast reactor JoyoShiba, Tomooki*; Sagara, Hiroshi*; Onishi, Takashi; Koyama, Shinichi; Maeda, Shigetaka; Han, C. Y.*; Saito, Masaki*
Annals of Nuclear Energy, 51, p.74 - 80, 2013/01
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)The design consideration of DU-Am oxide fuel pin was performed for Pu denaturing in the framework of the protected plutonium production based on the irradiation analyses of the depleted U (DU) samples irradiated in the environment of broad range of neutron energy in the experimental fast reactor Joyo. From the results of irradiation analyses of DU, it was confirmed that there is a strong dependence of transmutation behavior of DU on the resonance neutron ratio even in a fast reactor. Also, it was confirmed that there is a strong effect of sample material form and shape on generated Pu nuclide inventory especially near the reflector area (
20% resonance neutron ratio), because of the intensive self-shielding of 
U, though less is expected for Am. Sensitivity study of hypothetical DU-Am oxide fuel pellet irradiation on neutron energy and burn-up was performed to evaluate significant gradient of radial Pu isotopic composition profile (e.g., from 12 to 18% distribution in 3% Am doping, in 30% resonance neutron ratio and in 4.0
10
[n/cm
] of neutron fluence inside a large pellet with softened neutron spectrum), and vulnerability of the fuel pellet surface in terms of Pu denaturing was revealed. Design consideration of radial zoning of Am content was introduced to flatten the radial distribution of isotopic composition of Pu. The results of radial zoning of Am (4% and 3% of Am in the outer and inner zone of DU-Am oxide fuel pellet) in hypothetical irradiation neutronics analysis showed the radial profile of produced Pu is over 15 at.% of Pu isotopic composition in any zone and meets the criteria of Kimura et al. based on decay heat of Pu to impede utilization to fission explosive devices.
Onishi, Takashi; Koyama, Shinichi; Shiba, Tomooki*; Sagara, Hiroshi*; Saito, Masaki*
Progress in Nuclear Energy, 57, p.125 - 129, 2012/05
Times Cited Count：1 Percentile：10.1(Nuclear Science & Technology)In order to develop blanket fuel with high proliferation resistance in fast breeder reactor, chemical analysis of nine U samples irradiated in experimental fast reactor Joyo and Pu contents and Pu isotopic composition of the samples were measured. As results, dependence of Pu production behavior from U on neutron spectra was revealed.
Koyama, Shinichi; Osaka, Masahiko; Ito, Masahiko*; Sagara, Hiroshi*; Saito, Masaki*
Journal of Nuclear Science and Technology, 47(8), p.661 - 670, 2010/08
Times Cited Count：6 Percentile：40.12(Nuclear Science & Technology)A project on Protected Plutonium Production (P
) was proposed by Tokyo Institute of Technology as part of a non-proliferation research program for plutonium (Pu) utilization in nuclear reactors. A determination of Pu isotopes in 
Np samples irradiated in the experimental fast reactor JOYO was done to evaluate Pu production from Np under fast neutron spectra. In the mean time, 2, 5 and 10% Np-containing U samples were irradiated in the Advanced Test Reactor at the Idaho National Laboratory (INL) to evaluate Pu production in the thermal neutron region. The verified transmutation data can be used to design fuel pellets for non-proliferation.
Ota, Yukihiro; Nakai, Noriyuki; Nakamura, Hiroki; Machida, Masahiko; Inotani, Daisuke*; Ohashi, Yoji*; Koyama, Tomio*; Matsumoto, Hideki*
Physical Review B, 81(21), p.214511_1 - 214511_6, 2010/06
Times Cited Count：32 Percentile：75.32(Materials Science, Multidisciplinary)An extension of the Ambegaokar-Baratoff relation to a superconductor-insulator-superconductor (SIS) Josephson junction with multiple tunneling channels is derived. Applying the resultant relation to a SIS Josephson junction formed by an iron-based (five-band) and a single-band Bardeen-Cooper-Schrieffer (BCS) type superconductors, a theoretical bound of the Josephson critical current (
) multiplied by the resistance of the junction (
) is given. We reveal that such a bound is useful for identifying the pairing symmetry of iron-pnictide superconductors. One finds that if a measured value of 
is smaller than the bound then the symmetry is 
-wave, and otherwise -wave without any sign changes. In addition, we stress that temperature dependence of is sensitive to the difference of the gap functions from the BCS type gap formula in the above heterojunction.
Koyama, Shinichi; Osaka, Masahiko; Ito, Masahiko*; Sagara, Hiroshi*; Saito, Masaki*
Proceedings of International Conference on Advanced Nuclear Fuel Cycle; Sustainable Options & Industrial Perspectives (Global 2009) (CD-ROM), p.2356 - 2362, 2009/09
A project of Protected Plutonium Production was proposed by Tokyo-Tech as a part of non-proliferation research for Pu utilization to nuclear reactor. In order to validate this concept, two irradiation tests were performed. Experimental determination of Pu isotopes in Np samples irradiated in the experimental fast reactor JOYO was done to evaluate Pu production from Np under the fast neutron spectra. On the other hand, 2%, 5% and 10% Np containing U samples were also irradiated in Advanced Thermal Reactor of INL to evaluate the Pu production under thermal neutron region. The verified Np transmutation data can be used to design an Np-U mixed oxide fuel pellet for next phase Np-U fuel performance evaluations.
Ozawa, Masaki; Suzuki, Tatsuya*; Koyama, Shinichi; Akatsuka, Hiroshi*; Mimura, Hitoshi*; Fujii, Yasuhiko*
Progress in Nuclear Energy, 50(2-6), p.476 - 482, 2008/03
Times Cited Count：38 Percentile：90.4(Nuclear Science & Technology)For the minimization of the ecological burden originated in nuclear fuel recycling, a new R&D strategy was filed as "Adv.-ORIENT cycle". In the context, mutual precise separation of 
-elements, such as minor actinide (MA)/lanthanides (Lns) and Am/Cm, are highly essential for enhancing the MA (Am) burning. The separation and utilization of rare metal fission products (RMFPs; Ru, Tc, etc) are a new direction in the partitioning and transmutation field. Separation of exothermic nuclides, 
Sr, 
Cs as well as MA, will significantly help to improve the repository tasks. A key separation media are ion exchange chromatography (IXC) by tertiary pyridine resin and a catalytic electrolytic extraction (CEE) by Pd
. On challenging the isotope separation of LLFP, theoretical and laboratory studies were begun for 
Cs, 
Sn in the first priority.
CsOshita, Hironori; Ozawa, Masaki; Ishikawa, Makoto; Koyama, Shinichi; Akatsuka, Hiroshi*
JAEA-Review 2007-031, 41 Pages, 2007/09
JAEA-Review-2007-031.pdf:3.73MB
Recently establishment of self consistent nuclear fuel cycle has been required with respect to economical efficiency, safety and reduction of the load to the environment. Especially Cs included in spent fuel of nuclear power plants has extremely long half life (3.010
y) and its water solubility leads to the anxiety of exudation into ground water in geologic disposal. Recent technology development of laser has come to make it possible in principle to excite a specific isotope and separate it making use of the intrinsic physical and chemical properties of the excited state. This document reports the review of the isotope separation principle and its application to Cs separation.
Machida, Masahiko; Koyama, Tomio*; Ohashi, Yoji*
Physica C, 460-462(1), p.275 - 276, 2007/09
Times Cited Count：1 Percentile：6.68(Physics, Applied)no abstracts in English
Osaka, Masahiko; Miwa, Shuhei; Tanaka, Kosuke; Sato, Isamu; Hirosawa, Takashi; Obayashi, Hiroshi; Mondo, Kenji; Akutsu, Yoko; Ishi, Yohei; Koyama, Shinichi; et al.
WIT Transactions on Ecology and the Environment, Vol.105, p.357 - 366, 2007/06
no abstracts in English
Machida, Masahiko; Koyama, Tomio*; Ohashi, Yoji*
Physica C, 445-448, p.194 - 197, 2006/10
Times Cited Count：0 Percentile：0(Physics, Applied)no abstracts in English
Machida, Masahiko; Ohashi, Yoji*; Koyama, Tomio*
Physical Review A, 74(2), p.023621_1 - 023621_5, 2006/08
Times Cited Count：6 Percentile：31.7(Optics)no abstracts in English
Machida, Masahiko; Koyama, Tomio*; Ohashi, Yoji*
Physica C, 437-438, p.190 - 194, 2006/05
Times Cited Count：3 Percentile：17.95(Physics, Applied)no abstracts in English
Hamamoto, Shimpei; Iigaki, Kazuhiko; Shimizu, Atsushi; Sawahata, Hiroaki; Kondo, Makoto; Oyama, Sunao; Kawano, Shuichi; Kobayashi, Shoichi; Kawamoto, Taiki; Suzuki, Hisashi; et al.
JAEA-Technology 2006-030, 58 Pages, 2006/03
JAEA-Technology-2006-030.pdf:10.69MB
During normal operation of High Temperature engineering Test Reactor (HTTR) in Japan Atomic Energy Agency (JAEA), the reactivity is controlled by the Control Rods (CRs) system which consists of 32 CRs (16 pairs) and 16 Control Rod Drive Mechanisms (CRDMs). The CR system is located in stand-pipes accompanied by the Reserved Shutdown System (RSS). In the unlikely event that the CRs fail to be inserted, the RSS is provided to insert B
C/C pellets into the core. The RSS shall be designed so that the reactor should be held subcriticality from any operation condition by dropping in the pellets. The RSS consists of BC/C pellets, hoppers which contain the pellets, electric plug, driving mechanisms, guide tubes and so on. In accidents when the CRs cannot be inserted, an electric plug is pulled out by a motor and the absorber pellets fall into the core by gravity. A trouble, malfunction of one RSS out of sixteen, occurred during a series of the pre-start up checks of HTTR on February 21, 2005. We investigated the cause of the RSS trouble and took countermeasures to prevent the issue. As the result of investigation, the cause of the trouble was attributed to the following reason: In the motor inside, The Oil of grease of the multiplying gear flowed down from a gap of the oil seal which has been deformed and was mixed with abrasion powder of brake disk. Therefore the adhesive mixture prevented a motor from rotating.
