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Journal Articles

Structural changes of polystyrene particles in subcritical and supercritical water revealed by in situ small-angle neutron scattering

Shibata, Motoki*; Nakanishi, Yohei*; Abe, Jun*; Arima, Hiroshi*; Iwase, Hiroki*; Shibayama, Mitsuhiro*; Motokawa, Ryuhei; Kumada, Takayuki; Takata, Shinichi; Yamamoto, Katsuhiro*; et al.

Polymer Journal, 55(11), p.1165 - 1170, 2023/11

 Times Cited Count:0 Percentile:0(Polymer Science)

Journal Articles

Development of semiconductor switches for high-power crowbar circuits for J-PARC accelerator

Ono, Ayato; Takayanagi, Tomohiro; Fuwa, Yasuhiro; Shinozaki, Shinichi; Ueno, Tomoaki*; Horino, Koki*; Sugita, Moe; Yamamoto, Kazami; Kinsho, Michikazu; Ikoma, Naoya*; et al.

Proceedings of 20th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.871 - 876, 2023/11

In J-PARC, an ignitron is used for the crowbar device of the klystron power supply to excite the RF acceleration voltage in a Linac cavity. Mercury, that is used in the ignitron, would be prohibition of use in the future due to environmental protection. Therefore, we designed a semiconductor crowbar switch for short-circuit protection of klystron using a MOS gate thyristor. We have manufactured an oval-type board module that realizes an operating output of 3kV, 40kA, and 50us per board. Because a high voltage of 120 kV is applied on each board, we adopted a self-power supply method to supply a electricity for the control system. This method can create the electricity from a high-voltage DCDC converter. We confirmed the operating performance on a 1/2 scale (60 kV, 40 kA) of the voltage in the existing ignitron system (120 kV, 40 kA). We also studied a test circuit in a higher voltage range of more than 90 kV. Our latest result is well promising for an alternative system of ignitron.

Journal Articles

Consideration of high intensity single bunch acceleration in J-PARC RCS

Tamura, Fumihiko; Okita, Hidefumi; Hotchi, Hideaki*; Saha, P. K.; Meigo, Shinichiro; Yoshii, Masahito*; Omori, Chihiro*; Yamamoto, Masanobu; Seiya, Kiyomi*; Sugiyama, Yasuyuki*; et al.

Proceedings of 20th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.64 - 68, 2023/11

The J-PARC 3GeV synchrotron (RCS) provides high intensity proton beams to the Materials and Life Science Experimental Facility (MLF) and the Main Ring (MR). The harmonic number (h) of the RCS is 2 and the RCS normally accelerates two bunches. For some experiments at the MLF, a single bunch is preferred. In this case, one of the rf bucket is filled with protons and the other is empty. Therefore the beam intensity is halved. If the RCS can accelerate with h=1, the intensity per bunch can be doubled, enabling to provide single bunch beams to the MLF with the maximum intensity. This possibly increases the MR beam power by injecting high intensity single bunches eight times. In this presentation, we report mainly on the consideration of h=1 acceleration in the RCS by longitudinal simulations.

Journal Articles

Anomalous vortex dynamics in the spin-triplet superconductor UTe$$_2$$

Tokiwa, Yoshifumi; Sakai, Hironori; Kambe, Shinsaku; Opletal, P.; Yamamoto, Etsuji; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Yanase, Yoichi*; Haga, Yoshinori; et al.

Physical Review B, 108(14), p.144502_1 - 144502_5, 2023/10

The vortex dynamics in the spin-triplet superconductor, UTe$$_2$$, are studied by measuring the DC electrical resistivity with currents along the $$a$$-axis under magnetic fields along the $$b$$-axis. Surprisingly, we have discovered an island region of low critical current deep inside the superconducting (SC) state, well below the SC upper critical field, attributed to a weakening of vortex pinning. Notably, this region coincides with the recently proposed intermediate-field SC state. We discuss the possibility of nonsingular vortices in the intermediate state, where SC order parameter does not vanish entirely in the vortex cores due to the mixing of multiple SC components.

Journal Articles

Element-specific insight into ferromagnetic stability in UCoGe revealed by soft X-ray magnetic circular dichroism

Takeda, Yukiharu; Posp$'i$$v{s}$il, J.*; Yamagami, Hiroshi; Yamamoto, Etsuji; Haga, Yoshinori

Physical Review B, 108(8), p.085129_1 - 085129_10, 2023/08

Journal Articles

Internal event level-1 PRA for sodium-cooled fast reactor considering safety measures of defense-in-depth level 1 to 4

Nishino, Hiroyuki; Kurisaka, Kenichi; Naruto, Kenichi*; Gondai, Yoji; Yamamoto, Masaya

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 10 Pages, 2023/05

The effectiveness evaluation of safety measures against severe accident is necessary for restart of experimental sodium-cooled fast reactor "Joyo" in Japan. These safety measures correspond to those in defense-in-depth (DiD) level 4. In the previous study, a level-1 probabilistic risk assessment (PRA) at power was performed to calculate frequencies of the accident sequences of failure of safety measures in DiD level 1 to 3, to identify dominant accident sequence groups, and to identify dominant accident sequence for selecting important accident sequences in each accident sequence group which are needed for implementing the effectiveness evaluation of safety measures in DiD level 4. Based on this, the present study implemented level-1 PRA at power to show quantitatively reduction of those occurrence frequency by the safety measure in the DiD level 4. As the result, the frequency of each accident sequence group decreased significantly, and total frequency of the accident sequence groups decreased to about 1$$times$$10$$^{-6}$$ /reactor-year which is about 1/1000 times the one estimated in the previous study. The protected loss of heat sink was the largest contributor in all the accident groups and a dominant accident sequence in each accident group was also identified in this study.

Journal Articles

Ferromagnetic crossover within the ferromagnetic order of U$$_{7}$$Te$$_{12}$$

Opletal, P.; Sakai, Hironori; Haga, Yoshinori; Tokiwa, Yoshifumi; Yamamoto, Etsuji; Kambe, Shinsaku; Tokunaga, Yo

Journal of the Physical Society of Japan, 92(3), p.034704_1 - 034704_5, 2023/03

 Times Cited Count:0 Percentile:0(Physics, Multidisciplinary)

We investigate the physical properties of a single crystal of uranium telluride U$$_{7}$$Te$$_{12}$$. We have confirmed that U$$_{7}$$Te$$_{12}$$ crystallizes in the hexagonal structure with three nonequivalent crystallographic uranium sites. The paramagnetic moments are estimated to be approximately 1 $$mu_{B}$$ per the uranium site, assuming a uniform moment on all the sites. A ferromagnetic phase transition occurs at $$T_{rm C}$$= 48 K, where the in-plane magnetization increases sharply, whereas the out of-plane component does not increase significantly. With decreasing temperature further below $$T_{rm C}$$ under field-cooling conditions, the out-of-plane component increases rapidly around T$$^{star}$$= 26 K. In contrast, the in-plane component hardly changes at T$$^{star}$$. Specific heat measurement indicates no $$lambda$$-type anomaly around T$$^{star}$$, so this is a cross-over suggesting a reorientation of the ordering moments or successive magnetic ordering on the part of the multiple uranium sites.

Journal Articles

Japanese Evaluated Nuclear Data Library version 5; JENDL-5

Iwamoto, Osamu; Iwamoto, Nobuyuki; Kunieda, Satoshi; Minato, Futoshi; Nakayama, Shinsuke; Abe, Yutaka*; Tsubakihara, Kosuke*; Okumura, Shin*; Ishizuka, Chikako*; Yoshida, Tadashi*; et al.

Journal of Nuclear Science and Technology, 60(1), p.1 - 60, 2023/01

 Times Cited Count:17 Percentile:99.99(Nuclear Science & Technology)

Journal Articles

Development of semiconductor switches for high-power crowbar circuits

Ono, Ayato; Takayanagi, Tomohiro; Fuwa, Yasuhiro; Shinozaki, Shinichi; Ueno, Tomoaki*; Horino, Koki*; Sugita, Moe; Yamamoto, Kazami; Kinsho, Michikazu; Ikoma, Naoya*; et al.

Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.395 - 399, 2023/01

At J-PARC, an ignitron is used for the crowbar device of the klystron power supply for high-frequency acceleration of a linear accelerator. Ignitron uses mercury, which is of limited use worldwide, and is expected to be discontinued in the future. Therefore, we designed a semiconductor crowbar switch for short-circuit protection of klystron using a MOS gate thyristor. We have manufactured an oval-type board module that realizes an operating output of 3 kV, 40 kA, and 50 $$mu$$s per board. For the control power supply to each board module assuming a high voltage of 120 kV, we adopted a self-power supply method that creates a control power supply with a high-voltage DCDC converter from the voltage shared and charged by each board module. It was possible to confirm the operating performance on a 1/2 scale (60 kV, 40 kA) against the voltage of the existing equipment (120 kV, 40 kA) by connecting twenty oval board modules in series. The output test result will be reported.

Journal Articles

Semiconductor pulse power supplies for accelerators at J-PARC

Takayanagi, Tomohiro; Ono, Ayato; Fuwa, Yasuhiro; Shinozaki, Shinichi; Horino, Koki*; Ueno, Tomoaki*; Sugita, Moe; Yamamoto, Kazami; Oguri, Hidetomo; Kinsho, Michikazu; et al.

Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.242 - 246, 2023/01

At J-PARC, semiconductor short pulse power supplies to replace kicker power supplies and semiconductor long pulse power supplies to replace klystron power supply systems are under construction. We have fabricated a 40kV/2kA/1.2$$mu$$s unit power supply that employs a linear transformer drivers (LTD) system for kickers. Currently, we are working on a high voltage insulating cylinder insulator that suppresses corona discharges using only the insulator structure, without using insulating oil. In addition, the MARX system was adopted for klystron power supply system. A main circuit unit for 8kV/60A/830$$mu$$s rectangular pulse output and an 800V/60A correction circuit unit that improves the flat top droop from 10% to 1% were manufactured. Furthermore, a 2.2kV/2.4kW high voltage SiC inverter charger has been fabricated for this MARX power supply. The presentation will report the evaluation results of each test and prospects for semiconductor pulse power supplies.

Journal Articles

Measurement of the transverse asymmetry of $$gamma$$ rays in the $$^{117}$$Sn($$n,gamma$$)$$^{118}$$Sn reaction

Endo, Shunsuke; Okudaira, Takuya*; Abe, Ryota*; Fujioka, Hiroyuki*; Hirota, Katsuya*; Kimura, Atsushi; Kitaguchi, Masaaki*; Oku, Takayuki; Sakai, Kenji; Shima, Tatsushi*; et al.

Physical Review C, 106(6), p.064601_1 - 064601_7, 2022/12

 Times Cited Count:1 Percentile:55.85(Physics, Nuclear)

no abstracts in English

Journal Articles

Structural analysis of high-energy implanted Ni atoms into Si(100) by X-ray absorption fine structure spectroscopy

Entani, Shiro*; Sato, Shinichiro*; Honda, Mitsunori; Suzuki, Chihiro*; Taguchi, Tomitsugu*; Yamamoto, Shunya*; Oshima, Takeshi*

Radiation Physics and Chemistry, 199, p.110369_1 - 110369_7, 2022/10

 Times Cited Count:1 Percentile:35.78(Chemistry, Physical)

Ni silicide synthesis by Ni ion beam irradiation into Si attracts attention due to its advantages including the ability of formation of local structures, the controllability of ion beams, the formability of silicide without heat treatment and the high reproducibility of the resulting specimen. In this work, we investigate the local atomic structure of Si implanted with 3.0 MeV Ni$$^{+}$$ ions. Analysis of Ni K-edge fluorescent-yield extended X-ray absorption fine structure reveals that Ni atoms have mixed structure of metallic-like face-centered cubic Ni and NiSi$$_{2}$$ phases at the initial stage of the irradiation and the formation of NiSi$$_{2}$$ promotes significantly with the ion fluence above 10 $$^{15}$$ ions cm$$^{-2}$$. With consideration of the agreement between the ion fluence threshold for the structural transition and the critical Si-amorphization fluence, it is concluded that the amorphization of Si plays an important role in the synthesis of the NiSi$$_{2}$$ phase in Ni$$^{+}$$-irradiated Si.

Journal Articles

Design and actual performance of J-PARC 3 GeV rapid cycling synchrotron for high-intensity operation

Yamamoto, Kazami; Kinsho, Michikazu; Hayashi, Naoki; Saha, P. K.; Tamura, Fumihiko; Yamamoto, Masanobu; Tani, Norio; Takayanagi, Tomohiro; Kamiya, Junichiro; Shobuda, Yoshihiro; et al.

Journal of Nuclear Science and Technology, 59(9), p.1174 - 1205, 2022/09

 Times Cited Count:3 Percentile:82.38(Nuclear Science & Technology)

In the Japan Proton Accelerator Research Complex, the purpose of the 3 GeV rapid cycling synchrotron (RCS) is to accelerate a 1 MW, high-intensity proton beam. To achieve beam operation at a repetition rate of 25 Hz at high intensities, the RCS was elaborately designed. After starting the RCS operation, we carefully verified the validity of its design and made certain improvements to establish a reliable operation at higher power as possible. Consequently, we demonstrated beam operation at a high power, namely, 1 MW. We then summarized the design, actual performance, and improvements of the RCS to achieve a 1 MW beam.

Journal Articles

Structural 130 K phase transition and emergence of a two-ion Kondo state in Ce$$_2$$Rh$$_2$$Ga explored by $$^{69,71}$$Ga nuclear quadrupole resonance

Yamamoto, Shingo*; Fujii, Takuto*; Luther, S.*; Yasuoka, Hiroshi*; Sakai, Hironori; B$"a$rtl, F.*; Ranjith, K. M.*; Rosner, H.*; Wosnitza, J.*; Strydom, A. M.*; et al.

Physical Review B, 106(11), p.115125_1 - 115125_5, 2022/09

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

We have studied the microscopic magnetic properties, the nature of the 130 K phase transition, and the ground state in the recently synthesized compound Ce$$_2$$Rh$$_2$$Ga by use of $$^{69,71}$$Ga nuclear quadrupole resonance (NQR). The NQR spectra clearly show an unusual phase transition at $$T_tsim130$$ K, yielding a splitting of the high-temperature single NQR line into two well-resolved NQR lines, providing evidence for two crystallographically inequivalent Ga sites. The NQR frequencies are in good agreement with fully relativistic calculations of the band structure. Our NQR results indicate the absence of magnetic or charge order down to 0.3 K. The temperature dependence of the spin-lattice relaxation rate $$1/T_1$$ shows three distinct regimes, with onset temperatures at $$T_t$$ and 2 K. The temperature-independent $$1/T_1$$, observed between $$T_t$$ and 2 K, crosses over to a Korringa process, $$1/T_1propto T$$, below $$sim$$2 K, which evidences a rare two-ion Kondo scenario: The system evolves into a dense Kondo coherent state below 2.0 and 0.8 K probed by the two different Ga sites.

Journal Articles

Investigation of physical properties of glove for glove-box and estimation of its life-time

Kobayashi, Daisuke; Yamamoto, Masahiko; Nishida, Naoki; Miyoshi, Ryuta; Nemoto, Ryo*; Hayashi, Hiroyuki*; Kato, Keisuke; Nishino, Saki; Kuno, Takehiko; Kitao, Takahiko; et al.

Nihon Hozen Gakkai Dai-18-Kai Gakujutsu Koenkai Yoshishu, p.237 - 240, 2022/07

All gloves attached to glove-box in Tokai Reprocessing Plant have a fixed expiration date and have to be replaced every 4-year. However, degrees of glove deterioration are different depending on its usage environment (frequency, chemicals, radiation, etc.), because of rubber products. Therefore, physical properties such as tensile strength, elongation, hardness of gloves are measured, and the life-time of gloves are estimated. As a result, gloves without any defects in its appearance have enough physical property for acceptance criteria of new glove. The extrapolated physical property of glove is sufficiently larger than the reported values of damaged glove. No deterioration in physical properties of gloves, that are periodically replaced without any defects in its appearance, is observed and the usable life-time of the glove is estimated to be 8 years.

Journal Articles

Single crystal growth of superconducting UTe$$_2$$ by molten salt flux method

Sakai, Hironori; Opletal, P.; Tokiwa, Yoshifumi; Yamamoto, Etsuji; Tokunaga, Yo; Kambe, Shinsaku; Haga, Yoshinori

Physical Review Materials (Internet), 6(7), p.073401_1 - 073401_10, 2022/07

 Times Cited Count:9 Percentile:85.45(Materials Science, Multidisciplinary)

The molten salt flux method is applied as a new synthetic route for the single crystals of the spin-triplet superconductor UTe$$_2$$. The single crystals under an optimized growth condition with excess uranium exhibit a superconducting transition at $$T_{rm c}=2.1$$ K, which is the highest $$T_{rm c}$$ reported for this compound. The obtained crystals show a remarkably large residual resistivity ratio with respect to the room temperature value and a small residual electronic contribution in specific heat well below $$T_{rm c}$$. These results indicate that the increase of $$T_{rm c}$$ in UTe$$_2$$ can be achieved by reducing the disorder associated with uranium vacancies. The excess uranium in the molten salt acts as a reducing agent, preventing tetravalent uranium from becoming pentavalent and suppressing creation of uranium vacancies. At the same time, the relatively low growth temperature can suppress Te volatilization.

Journal Articles

Sodium-cooled Fast Reactors

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.

Journal Articles

Hydrogen absorption and diffusion behaviors in cube-shaped palladium nanoparticles revealed by ambient-pressure X-ray photoelectron spectroscopy

Tang, J.*; Seo, O.*; Rivera Rocabado, D. S.*; Koitaya, Takanori*; Yamamoto, Susumu*; Namba, Yusuke*; Song, C.*; Kim, J.*; Yoshigoe, Akitaka; Koyama, Michihisa*; et al.

Applied Surface Science, 587, p.152797_1 - 152797_8, 2022/06

 Times Cited Count:6 Percentile:77.85(Chemistry, Physical)

The hydrogen absorption and diffusion mechanisms on cube-shaped Pd nanoparticles (NPs) which are important hydrogen-storage materials were studied using X-ray photoelectron spectroscopy and DFT calculations. In the surface region, hydrogen absorption showed almost similar behavior regardless of the NPs size. It was found that the octahedral sites are more favorable than the tetrahedral sites for hydrogen occupation. We also clarified that the hydrogen atoms absorbing on the smaller-sized Pd NPs diffuse to the subsurface more actively because of the weakened Pd-H bond by the surface disordering, which plays an important role in hydrogen adsorption at a low H$$_{2}$$ pressure.

Journal Articles

Effect of uranium deficiency on normal and superconducting properties in unconventional superconductor UTe$$_2$$

Haga, Yoshinori; Opletal, P.; Tokiwa, Yoshifumi; Yamamoto, Etsuji; Tokunaga, Yo; Kambe, Shinsaku; Sakai, Hironori

Journal of Physics; Condensed Matter, 34(17), p.175601_1 - 175601_7, 2022/04

 Times Cited Count:14 Percentile:90.93(Physics, Condensed Matter)

Journal Articles

Electronic structure of ThPd$$_2$$Al$$_3$$; Impact of the U $$5f$$ states on the electronic structure of UPd$$_2$$Al$$_3$$

Fujimori, Shinichi; Takeda, Yukiharu; Yamagami, Hiroshi; Posp$'i$$v{s}$il, J.*; Yamamoto, Etsuji; Haga, Yoshinori

Physical Review B, 105(11), p.115128_1 - 115128_6, 2022/03

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

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