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Journal Articles

Latent ion tracks were finally observed in diamond

Amekura, Hiroshi*; Chettah, A.*; Narumi, Kazumasa*; Chiba, Atsuya*; Hirano, Yoshimi*; Yamada, Keisuke*; Yamamoto, Shunya*; Leino, A. A.*; Djurabekova, F.*; Nordlund, K.*; et al.

Nature Communications (Internet), 15, p.1786_1 - 1786_10, 2024/02

Injecting high-energy heavy ions in the electronic stopping regime into solids can create cylindrical damage zones called latent ion tracks. Although these tracks form in many materials, none have ever been observed in diamond, even when irradiated with high-energy GeV uranium ions. Here we report the first observation of ion track formation in diamond irradiated with 2-9 MeV C$$_{60}$$ fullerene ions. Depending on the ion energy, the mean track length (diameter) changed from 17 (3.2) nm to 52 (7.1) nm. High resolution scanning transmission electron microscopy (HR-STEM) indicated the amorphization in the tracks, in which $$pi$$-bonding signal from graphite was detected by the electron energy loss spectroscopy (EELS).

Journal Articles

Characterization and corrosion behavior of Al-added high Mn ODS austenitic steels in oxygen-saturated lead-bismuth eutectic

Haoran, W.*; Yu, H.*; Liu, J.*; Kondo, Sosuke*; Okubo, Nariaki; Kasada, Ryuta*

Corrosion Science, 209, p.110818_1 - 110818_12, 2022/12

 Times Cited Count:1 Percentile:34.75(Materials Science, Multidisciplinary)

The corrosion behavior of newly developed Al$$_{2}$$O$$_{3}$$ forming high Mn oxide dispersion strengthened (ODS) austenitic steels was examined in oxygen-saturated lead-bismuth eutectic at 450$$^{circ}$$C for 430 h. Compared with non-ODS steels, the ODS steels possessed superior resistance to corrosion and spallation. The high density grain boundaries in the ODS steels acted as channels for the rapid outward diffusion of metallic elements, forming an internal continuous Cr$$_{2}$$O$$_{3}$$ scale at the original surface. Accelerated Al diffusion, along with oxidation prevention by the external (Fe, Mn) oxide scale and the internal Cr$$_{2}$$O$$_{3}$$ scale, jointly resulted in the formation of a continuous Al-rich oxide scale in ODS-7Al steel, contributing to its superior corrosion resistance.

JAEA Reports

Development of high temperature LBE corrosion test loop "OLLOCHI"

Saito, Shigeru; Wan, T.*; Okubo, Nariaki; Kita, Satoshi*; Obayashi, Hironari; Sasa, Toshinobu

JAEA-Technology 2021-034, 94 Pages, 2022/03

JAEA-Technology-2021-034.pdf:5.91MB

Lead-bismuth eutectic alloy (LBE) is a major candidate for a spallation target material and core coolant of an accelerator driven system (ADS) which has been developed in the Japan Atomic Energy Agency (JAEA) to transmute high-level radioactive wastes. A proton irradiation facility to build a material irradiation database for future ADS development is under considering in the J-PARC. To realize both the ADS and the above-mentioned facility, there are many issues on operational safety of LBE to be solved. Especially, corrosion data for the major materials such as T91 (Modified 9Cr-1Mo steel) and SS316L at the temperature range between 400 and 550 $$^{circ}$$C under the conditions of flowing LBE with a controlled oxygen are not sufficient to design the ADS and the facility. JAEA developed a new large-scale corrosion test loop named "OLLOCHI (Oxygen-controlled LBE LOop for Corrosion tests in HIgh-temperature)" aiming to perform the compatibility tests between the LBE and the steels, as well as to develop the LBE operation technology. OLLOCHI has a function to automatically control the oxygen concentration in LBE. The maximum temperature at the regions of high-temperature and low-temperature of the OLLOCHI are 550 $$^{circ}$$C and 450 $$^{circ}$$C respectively to cover the ADS designed condition. As a result of 2,000 hours operation, it was demonstrated that the OLLOCHI showed the designed performance. In this report, outline of the OLLOCHI, details of the components, results of characteristic tests, and the future experimental plan are described.

Journal Articles

Durability of secondary electron emission for high-intensity beam on SiC wire

Meigo, Shinichiro; Nakano, Keita; Okubo, Nariaki; Yuyama, Takahiro*; Ishii, Yasuyuki*

Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.296 - 301, 2021/10

no abstracts in English

Journal Articles

Effect of irradiation on corrosion behavior of 316L steel in lead-bismuth eutectic with different oxygen concentrations

Okubo, Nariaki; Fujimura, Yuki; Tomobe, Masakatsu*

Quantum Beam Science (Internet), 5(3), p.27_1 - 27_9, 2021/09

In an accelerator driven system (ADS), the beam window material of the spallation neutron target is heavily irradiated under severe conditions. Displacement damage and corrosion occur simultaneously because of high-energy neutron and/or proton irradiation in the lead-bismuth flow. The materials used in ADSs need to be compatible with the liquid metal, which is lead-bismuth eutectic (LBE), to prevent issues such as liquid metal embrittlement (LME) and liquid metal corrosion (LMC). In this study, the LMC behavior after ion irradiation of 316L austenitic steel is considered for self-ion irradiations followed by the corrosion tests. The 316L specimens were irradiated by 10.5 MeV-Fe$$^{3+}$$ ions at temperature of 450$$^{circ}$$C up to 50 displacement per atom (dpa). After the corrosion test at 450$$^{circ}$$C in LBE with low oxygen concentration, the surface of the non-irradiated area was not oxidized but corrosive morphology with pits, whereas the irradiated area was covered by an iron/chromium oxide layer. The surface of the irradiated area was covered by the duplex layers of iron and iron/chromium oxides in the case of higher oxygen concentration in LBE. It is suggested that irradiation can advance oxide layer formation because of enhanced Fe diffusion caused by the residual vacancies in 316L steel.

Journal Articles

Radiation damage mechanism in ceramics irradiated with swift heavy ions

Ishikawa, Norito; Taguchi, Tomitsugu*; Okubo, Nariaki

Shototsu, 18(3), p.43 - 55, 2021/05

Radiation damage mechanism in ceramics irradiated with swift heavy ions has been studied by using transmission electron microscopy (TEM). We introduce how the mechanisms are unveiled by our recent TEM studies.

JAEA Reports

Manufacturing miniature beam window for accelerator-driven system by cutting T91 steel

Watanabe, Nao; Sugawara, Takanori; Okubo, Nariaki; Nishihara, Kenji

JAEA-Technology 2020-026, 59 Pages, 2021/03

JAEA-Technology-2020-026.pdf:3.95MB

As a part of partitioning and transmutation technology development to reduce the burden of radioactive disposal, an investigation of Accelerator-Driven System (ADS) has been performed by Japan Atomic Energy Agency. A beam window, which is an inherent structure of the ADS, is planned to be made from T91 steel and its shape is a thin hemisphere shell. However, it had never been tried to manufacture it out of T91 steel. In this investigation, we tried to manufacture miniature beam windows by cutting T91 steel, and to discuss the process, manufacturing accuracy and geometry measurement methods. As a result, considering a real scale ADS beam window, a figure error between designing and machining ones is estimated to be about 5%. Its effect would be very small to the structural strength.

Journal Articles

Status of LBE study and experimental plan at JAEA

Saito, Shigeru; Wan, T.*; Okubo, Nariaki; Obayashi, Hironari; Watanabe, Nao; Ohdaira, Naoya*; Kinoshita, Hidetaka; Yamaki, Kenichi*; Kita, Satoshi*; Yoshimoto, Hidemitsu*; et al.

JPS Conference Proceedings (Internet), 33, p.011041_1 - 011041_6, 2021/03

An Accelerator Driven System (ADS) for waste transmutation investigated in JAEA employs lead-bismuth eutectic (LBE) as a neutron production target material and coolant. The neutrons are to be produced via the spallation with 1.5 GeV proton beam injection. As materials irradiation data are important for ADS development, JAEA plans to construct an irradiation facility with LBE neutron production target in J-PARC. There are many technical issues on LBE for practical use. In JAEA, various R&Ds are being carried out. Concerning corrosion study, conditioning operation and functional tests of OLLOCHI started. Oxygen concentration control technology has also developing. In the large scale LBE loop experiment, the operation for steady state and transient experiments was performed by using IMMORTAL. In the area of instrument, development of ultrasonic flow meter and freeze seal valve are progressing as a key technology for the LBE loop system. Investigation of behavior of impurities in LBE, which is important for design of the irradiation facility, started. In this paper, the status of the LBE studies and experimental plan will be presented.

Journal Articles

Ion tracks in silicon formed by much lower energy deposition than the track formation threshold

Amekura, Hiroshi*; Toulemonde, M.*; Narumi, Kazumasa*; Li, R.*; Chiba, Atsuya*; Hirano, Yoshimi*; Yamada, Keisuke*; Yamamoto, Shunya*; Ishikawa, Norito; Okubo, Nariaki; et al.

Scientific Reports (Internet), 11(1), p.185_1 - 185_11, 2021/01

 Times Cited Count:10 Percentile:75.98(Multidisciplinary Sciences)

We report the track formation of 10 nm in diameter in silicon irradiated with 6 MeV C$$_{60}$$, i.e., much lower energy than the previously reported energy threshold.

Journal Articles

Irradiation effects of swift heavy ions detected by refractive index depth profiling

Amekura, Hiroshi*; Li, R.*; Okubo, Nariaki; Ishikawa, Norito; Chen, F.*

Quantum Beam Science (Internet), 4(4), p.39_1 - 39_11, 2020/12

Evolution of depth profiles of the refractive index in Y$$_{3}$$Al$$_{5}$$O$$_{12}$$ (YAG) crystals were studied under 200 MeV Xe ion irradiation. The index changes were observed at three different depth regions; (i) a plateau near the surface between 0 and 3 $$mu$$m in depth, which can be ascribed to the electronic stopping Se, (ii) a broad peak at 6 $$mu$$m in depth, and (iii) a sharp dip at 13 $$mu$$m in depth, which is attributed to the nuclear stopping Sn peak.

Journal Articles

Corrosion behaviour of Al-added high Mn austenitic steels in molten lead bismuth eutectic with saturated and low oxygen concentrations at 450$$^{circ}$$C

Wang, H.*; Yu, H.*; Kondo, Sosuke*; Okubo, Nariaki; Kasada, Ryuta*

Corrosion Science, 175, p.108864_1 - 108864_12, 2020/10

 Times Cited Count:19 Percentile:85.44(Materials Science, Multidisciplinary)

Corrosion tests were performed on newly developed alumina-forming austenitic (AFA) steels in stagnant lead bismuth eutectic (LBE) with saturated and low oxygen concentrations at 450$$^{circ}$$C for 430 h. The steels exhibited enhanced corrosion resistance to the LBE environments with the increasing of Al content. A continuous and protective Al-rich oxide scale formed on the steel specimens that were exposed to LBE with a low oxygen concentration, whereas a non-protective and stratified oxide scale formed in the oxygen saturated LBE.

Journal Articles

Swift heavy ion irradiation to non-amorphizable CaF$$_{2}$$ and amorphizable Y$$_{3}$$Al$$_{5}$$O$$_{12}$$ (YAG) crystals

Amekura, Hiroshi*; Li, R.*; Okubo, Nariaki; Ishikawa, Norito; Chen, F.*

Nuclear Instruments and Methods in Physics Research B, 474, p.78 - 82, 2020/07

 Times Cited Count:5 Percentile:54.54(Instruments & Instrumentation)

Yttrium-aluminum-garnet (YAG) and calcium fluoride (CaF$$_{2}$$) were irradiated with 200 MeV Xe ions. YAG crystal was transformed to an amorphous phase, whereas CaF$$_{2}$$ shows the non-amorphizable nature. In spite of amorphization, YAG maintained its transparency, whereas CaF$$_{2}$$ markedly loses it transparency showing a broad absorption band centered at 550 nm.

Journal Articles

Matrix-material dependence on the elongation of embedded gold nanoparticles induced by 4 MeV C$$_{60}$$ and 200 MeV Xe ion irradiation

Li, R.*; Narumi, Kazumasa*; Chiba, Atsuya*; Hirano, Yu*; Tsuya, Daiju*; Yamamoto, Shunya*; Saito, Yuichi*; Okubo, Nariaki; Ishikawa, Norito; Pang, C.*; et al.

Nanotechnology, 31(26), p.265606_1 - 265606_9, 2020/06

 Times Cited Count:5 Percentile:33.73(Nanoscience & Nanotechnology)

We report the elongation of embedded Au nanoparticles (NPs) in three different matrices under irradiations of 4 MeV C$$_{60}$$ ions and 200 MeV Xe ions. Large elongation of Au NPs was observed for crystalline indium tin oxide (ITO) under both 4 MeV C$$_{60}$$ and 200 MeV Xe irradiation. The ITO layer preserved the crystallinity even after large elongation was induced. This is the first report of the elongation of metal NPs in a crystalline matrix.

Journal Articles

Degradation prediction of a gamma-ray radiation dosimeter using InGaP solar cells in a primary containment vessel of the Fukushima Daiichi Nuclear Power Station

Okuno, Yasuki; Yamaguchi, Masafumi*; Okubo, Nariaki; Imaizumi, Mitsuru*

Journal of Nuclear Science and Technology, 57(4), p.457 - 462, 2020/04

 Times Cited Count:7 Percentile:62.49(Nuclear Science & Technology)

Indium gallium phosphide (InGaP) solar cell with a superior high-radiation resistance is expected to be a powerful candidate for a dosimeter under a high-radiation dose rate environment. In this study, in order to predict the lifetime as the dosimeter using the InGaP solar cell, we clarify the effect of minority-carrier diffusion length ($$L$$) on a radiation-induced current as a dose signal in the InGaP solar cell by irradiation tests and empirical calculations. In the irradiation tests, the short circuit current density ($$J_{rm sc}$$) as a function of the gamma-ray dose rate is measured to estimate the $$L$$ for the InGaP solar cell by irradiation tests. The operational lifetime as a detector using the InGaP solar cell under various dose rates is estimated by using the empirical calculations based on the relation between the L and absorbed dose. The results suggest that the dosimeter using InGaP solar cell is able to be used during more than 10 h in the primary containment vessel of the Fukushima Daiichi Nuclear Power Plant and it has a high potential of being a radiation-resistant dosimeter that would contribute to the decommissioning.

Journal Articles

Current Status of R&D and PIE Program for ADS Material Development in JAEA

Saito, Shigeru; Okubo, Nariaki; Obayashi, Hironari; Wan, T.; Sugawara, Takanori; Sasa, Toshinobu; Maekawa, Fujio

JPS Conference Proceedings (Internet), 28, p.071003_1 - 071003_6, 2020/02

Japan Atomic Energy Agency (JAEA) proposes transmutation of minor actinides (MA) by accelerator-driven systems (ADS). The ADS designed by JAEA is a system composed by LBE (Lead-Bismuth Eutectic) spallation target and a subcritical core. In the ADS, a beam window (BW) is exposed in complex field of heavy irradiation by proton/neutron and corrosion by flowing LBE. To develop ADS structural materials, it is of critical importance to investigate materials used in such environment. Thus, JAEA plans to construct a proton irradiation facility at the J-PARC to prepare an irradiation database for candidate ADS structural materials and to investigate irradiation effects in flowing LBE environment. In this paper, giving a whole scope of the JAEA ADS development, some results of experimental measurements and the specific program for planed R&D will be presented.

Journal Articles

Application of InGaP space solar cells for a radiation dosimetry at high dose rates environment of Fukushima Daiichi Nuclear Power Plant

Okuno, Yasuki; Okubo, Nariaki; Imaizumi, Mitsuru*

Journal of Nuclear Science and Technology, 56(9-10), p.851 - 858, 2019/09

 Times Cited Count:12 Percentile:75.06(Nuclear Science & Technology)

Decommissioning the Fukushima Daiichi Nuclear Power Plant (1F) after the accident caused by a tsunami in 2011 requires characterization of the fuel debris by dose distribution measurement. This paper describes the experimental and theoretical behavior of a radiation detector applied with InGaP solar cells is investigated and allow the localization and characterization of the fuel debris. In the irradiation test, it was observed that the radiation-induced current output of the InGaP solar cells increases linearly with increasing dose rates of $$^{60}$$Co $$gamma$$-ray. For measurements at low dose rates, it becomes clear that the minimum detectable dose rate and resolution can be determined by analyzing the noise characterization. The maximum detection limit of radiation dosimetry for the InGaP solar cell was found to be higher than the highest $$gamma$$-ray dose rate observable at the reactor core for 1F plants. Additionally, as an analysis of the radiation-induced current, it is attempted to express a relational expression between the absorbed dose rate and the creation of radiation-induced current pairs in the solar cells. The experimental and simulation results suggest that solar cells can be powerful tools for radiation dosimetry in high dose rate environments near the debris of the 1F plant.

Journal Articles

Structure of nitride layer formed on titanium alloy surface by N$$_{2}$$-gas exposure at high temperatures

Takeda, Yusuke; Iida, Kiyoshi*; Sato, Shinji*; Matsuo, Tadatoshi*; Nagashima, Yasuyuki*; Okubo, Nariaki; Kondo, Keietsu; Hirade, Tetsuya

JPS Conference Proceedings (Internet), 25, p.011023_1 - 011023_3, 2019/03

In this study, we prepared samples under two different conditions, (1) 810$$^{circ}$$C, for 600 min, and (2) 850$$^{circ}$$C, for 720 min. A depth-profile analysis of the surfaces of the samples is conducted through Doppler broadening (DB) measurements of positron annihilation $$gamma$$ rays using a slow positron beam. It was indicated that many of positrons annihilated in defects near the surface. According to the TEM image, there are nano-crystal grains near the surface and then positrons can diffuse in the grains and annihilate in defects at the grain boundaries. Furthermore, DB measurements indicated that there is a depth dependence on the chemical composition where positrons annihilate. EDS spectroscopy measurements also indicated that there is a depth dependence of impurities such as Vanadium. These results indicated change of the chemical composition at the grain boundaries.

Journal Articles

Influence of gamma-ray irradiation on mechanical property of YSZ for oxygen sensors in ADS

Okubo, Nariaki; Okuno, Yasuki; Kitamura, Akane; Taguchi, Tomitsugu*

Nuclear Instruments and Methods in Physics Research B, 435, p.198 - 202, 2018/11

 Times Cited Count:2 Percentile:21.23(Instruments & Instrumentation)

Accelerator driven system (ADS) adopts the lead-bismuth eutectic (LBE) as both coolant and spallation target. The oxygen concentration control is one of the most important technical developments. Estimation of durability under gamma-ray irradiation for the oxygen sensor is necessary for the integrity evaluation of ADS components. The Zirconia added by Yttria (YSZ) is the main element in oxygen sensor. Effect of gamma-ray irradiation on the mechanical property and structural change for three types of YSZ with 3, 6, 8 mol% Yttria was evaluated by using 4 points bend test, XRD, SEM and Raman spectroscope. The gamma-ray irradiations were conducted at 1 and 2 kGy/h, which corresponded to the LBE activity after 1 year ADS operation. In the cases of 8Y and 6Y, degradation of strength was not measured and the fracture surface did not change the morphology. In the case of 3Y, however, the strength did not change but phase transformation from tetragonal to monoclinic crystal structure was observed in XRD results, depending on the irradiation dose. This implies that the gamma-ray irradiation causes the phase transformation in 3Y-YSZ.

Journal Articles

Ag nanoparticles embedded in Nd:YAG crystals irradiated with tilted beam of 200 MeV Xe ions; Optical dichroism correlated to particle reshaping

Li, R.*; Pang, C.*; Amekura, Hiroshi*; Ren, F.*; H$"u$bner, R.*; Zhou, S.*; Ishikawa, Norito; Okubo, Nariaki; Chen, F.*

Nanotechnology, 29(42), p.424001_1 - 424001_8, 2018/10

 Times Cited Count:5 Percentile:25.59(Nanoscience & Nanotechnology)

We report on the fabrication of reshaped Ag nanoparticles (NPs) embedded in a Nd:YAG crystal by combining Ag ion implantation and swift heavy Xe ion irradiation. The localized surface plasmon resonance (LSPR) effect is proved to be efficiently modulated according to the phenomenon of polarization-dependent absorption. The LSPR peak located at 448 nm shows red shift and blue shift at 0 degree and 90 degree polarization, respectively, which is in good agreement with calculation by discrete dipole approximation. Based on the near-field intensity distribution, the interaction between reshaped NPs shows a non-ignorable effect on the optical absorption. Furthermore, the polarization-dependence of the photoluminescence (PL) intensity is analyzed, which is positively related to the modulated LSPR absorption. It demonstrates the potential of the enhancement of PL intensity by embedded plasmonic Ag NPs.

JAEA Reports

Measurement experiment of oxygen concentration in liquid lead-bismuth eutectic; Basic Tests and estimation of gamma-ray irradiation effect

Sugawara, Takanori; Kita, Satoshi*; Yoshimoto, Hidemitsu*; Okubo, Nariaki

JAEA-Technology 2018-008, 26 Pages, 2018/09

JAEA-Technology-2018-008.pdf:10.35MB

The oxygen sensors to measure the oxygen concentration in liquid LBE (lead-bismuth eutectic) were fabricated and tested for future use in LBE-cooled ADS (accelerator-driven system) or LBE test loops. The following tests were performed; estimation of catalyst application range, freeze seal structure and estimation of gamma-ray irradiation effect. For the estimation of the catalyst application range, it was confirmed that the measurement accuracy became worse in low LBE temperature as the application range became small. For the freeze seal structure, we realized the structure to prevent the LBE leakage with 0.5 MPa pressure condition. For the estimation of gamma-ray irradiation effect, the ex-situ test was carried out and it was observed that there was little effect by 4 MGy gamma-ray irradiation.

118 (Records 1-20 displayed on this page)