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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

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

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

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

Spallation and fragmentation cross sections for 168 MeV/nucleon $$^{136}$$Xe ions on proton, deuteron, and carbon targets

Sun, X. H.*; Wang, H.*; Otsu, Hideaki*; Sakurai, Hiroyoshi*; Ahn, D. S.*; Aikawa, Masayuki*; Fukuda, Naoki*; Isobe, Tadaaki*; Kawakami, Shunsuke*; Koyama, Shumpei*; et al.

Physical Review C, 101(6), p.064623_1 - 064623_12, 2020/06

 Times Cited Count:5 Percentile:53.56(Physics, Nuclear)

The spallation and fragmentation reactions of $$^{136}$$Xe induced by proton, deuteron and carbon at 168 MeV/nucleon were studied at RIKEN Radioactive Isotope Beam Factory via the inverse kinematics technique. The cross sections of the lighter products are larger in the carbon-induced reactions due to the higher total kinetic energy of carbon. The energy dependence was investigated by comparing the newly obtained data with previous results obtained at higher reaction energies. The experimental data were compared with the results of SPACS, EPAX, PHITS and DEURACS calculations. These data serve as benchmarks for the model calculations.

Journal Articles

How different is the core of $$^{25}$$F from $$^{24}$$O$$_{g.s.}$$ ?

Tang, T. L.*; Uesaka, Tomohiro*; Kawase, Shoichiro; Beaumel, D.*; Dozono, Masanori*; Fujii, Toshihiko*; Fukuda, Naoki*; Fukunaga, Taku*; Galindo-Uribarri, A.*; Hwang, S. H.*; et al.

Physical Review Letters, 124(21), p.212502_1 - 212502_6, 2020/05

 Times Cited Count:14 Percentile:74.77(Physics, Multidisciplinary)

The structure of a neutron-rich $$^{25}$$F nucleus is investigated by a quasifree ($$p,2p$$) knockout reaction. The sum of spectroscopic factors of $$pi 0d_{5/2}$$ orbital is found to be 1.0 $$pm$$ 0.3. The result shows that the $$^{24}$$O core of $$^{25}$$F nucleus significantly differs from a free $$^{24}$$O nucleus, and the core consists of $$sim$$35% $$^{24}$$O$$_{rm g.s.}$$, and $$sim$$65% excited $$^{24}$$O. The result shows that the $$^{24}$$O core of $$^{25}$$F nucleus significantly differs from a free $$^{24}$$O nucleus. The result may infer that the addition of the $$0d_{5/2}$$ proton considerably changes the neutron structure in $$^{25}$$F from that in $$^{24}$$O, which could be a possible mechanism responsible for the oxygen dripline anomaly.

Journal Articles

Conceptual study on parasitic low-energy RI beam production with in-flight separator BigRIPS and the first stopping examination for high-energy RI beams in the parasitic gas cell

Sonoda, Tetsu*; Katayama, Ichiro*; Wada, Michiharu*; Iimura, Hideki; Sonnenschein, V.*; Iimura, Shun*; Takamine, Aiko*; Rosenbusch, M.*; Kojima, Takao*; Ahn, D. S.*; et al.

Progress of Theoretical and Experimental Physics (Internet), 2019(11), p.113D02_1 - 113D02_12, 2019/11

AA2019-0315.pdf:1.37MB

 Times Cited Count:1 Percentile:11.76(Physics, Multidisciplinary)

An in-flight separator, BigRIPS, at RIBF in RIKEN provides each experiment with specific nuclides separated from many nuclides produced by projectile fragmentation or in-flight fission. In this process, nuclides other than separated ones are discarded on the slits in BigRIPS, although they include many nuclides interested from the view point of nuclear structure. In order to extract these nuclides for parasitic experiments, we are developing a method using laser ion-source (PALIS). A test experiment with $$^{78}$$Se beam from RIBF has been performed by using a gas cell set in BigRIPS. Unstable nuclides around $$^{67}$$Se were stopped in the gas cell in accordance with a calculation using LISE code. The stopping efficiency has been estimated to be about 30%. As a next step, we will establish the technique for extracting reaction products from the gas cell.

Journal Articles

Nowcast and forecast of galactic cosmic ray (GCR) and solar energetic particle (SEP) fluxes in magnetosphere and ionosphere; Extension of WASAVIES to earth orbit

Sato, Tatsuhiko; Kataoka, Ryuho*; Shiota, Daiko*; Kubo, Yuki*; Ishii, Mamoru*; Yasuda, Hiroshi*; Miyake, Shoko*; Miyoshi, Yoshizumi*; Ueno, Haruka*; Nagamatsu, Aiko*

Journal of Space Weather and Space Climate (Internet), 9, p.A9_1 - A9_11, 2019/03

 Times Cited Count:6 Percentile:39.39(Astronomy & Astrophysics)

Real-time estimation of astronaut doses during solar particle events (SPE) is one of the most challenging tasks in cosmic-ray dosimetry. We therefore develop a new computational method that can nowcast the solar energetic particle (SEP) as well as galactic cosmic-ray (GCR) fluxes on any Earth orbit during a large SPE associating with ground level enhancement. It is an extended version of WArning System for AVIation Exposure to Solar Energetic Particle, WASAVIES. The extended version, called WASAVIES-EO, can calculate the GCR and SEP fluxes outside a satellite based on its two-line element data. Moreover, organ dose and dose-equivalent rates of astronauts in the International Space Station (ISS) can be estimated using the system, considering its shielding effect. The accuracy of WASAVIES-EO was validated based on the dose rates measured in ISS, as well as based on high-energy proton fluxes observed by POES satellites.

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.

Journal Articles

Vaporlike phase of amorphous SiO$$_{2}$$ is not a prerequisite for the core/shell ion tracks or ion shaping

Amekura, Hiroshi*; Kluth, P.*; Mota-Santiago, P.*; Sahlberg, I.*; Jantunen, V.*; Leino, A. A.*; Vazquez, H.*; Nordlund, K.*; Djurabekova, F.*; Okubo, Nariaki; et al.

Physical Review Materials (Internet), 2(9), p.096001_1 - 096001_10, 2018/09

 Times Cited Count:10 Percentile:38.08(Materials Science, Multidisciplinary)

When a swift heavy ion (SHI) penetrates amorphous SiO$$_{2}$$, a core/shell (C/S) ion track is formed due to vaporization, where the ion track consists of a lower-density core and a higher-density shell. Here we reexamine this hypothesis. The MD simulations indicate that the vaporization is not induced under 50-MeV Si irradiation ($$Se$$ = 3 keV/nm), but the C/S tracks and the ion shaping of nanoparticles are nevertheless induced. Thus, the vaporization is not a prerequisite for the C/S tracks and the ion shaping.

Journal Articles

Nuclear magnetic field in solids detected with negative-muon spin rotation and relaxation

Sugiyama, Jun*; Umegaki, Izumi*; Nozaki, Hiroshi*; Higemoto, Wataru; Hamada, Koji*; Takeshita, Soshi*; Koda, Akihiro*; Shimomura, Koichiro*; Ninomiya, Kazuhiko*; Kubo, Kenya*

Physical Review Letters, 121(8), p.087202_1 - 087202_5, 2018/08

 Times Cited Count:17 Percentile:74.81(Physics, Multidisciplinary)

Journal Articles

Real time and automatic analysis program for WASAVIES; Warning system for aviation exposure to solar energetic particles

Sato, Tatsuhiko; Kataoka, Ryuho*; Shiota, Daiko*; Kubo, Yuki*; Ishii, Mamoru*; Yasuda, Hiroshi*; Miyake, Shoko*; Park, I.*; Miyoshi, Yoshizumi*

Space Weather, 16(7), p.924 - 936, 2018/07

 Times Cited Count:17 Percentile:68.44(Astronomy & Astrophysics)

A physics-based warning system of aviation exposure to solar energetic particles, WASAVIES, is improved to be capable of real-time and automatic analysis. In the improved system, the count rates of several neutron monitors (NM) at the ground level, as well as the proton fluxes measured by the GOES satellite are continuously downloaded at intervals of 5 min and used for determining the model parameters. The performance of WASAVIES is examined by analyzing the three major GLE events of the 21st century. A web-interface of WASAVIES is also developed and will be released in the near future through the public server of NICT.

Journal Articles

Status report of the chopper spectrometer 4SEASONS

Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Kamazawa, Kazuya*; Ikeuchi, Kazuhiko*; Iida, Kazuki*; Ishikado, Motoyuki*; Murai, Naoki; Kira, Hiroshi*; Nakatani, Takeshi; et al.

Journal of Physics; Conference Series, 1021(1), p.012030_1 - 012030_6, 2018/06

BB2016-1727.pdf:0.39MB

 Times Cited Count:3 Percentile:88.81

Journal Articles

Emergent Weyl fermion excitations in TaP explored by $$^{181}$$Ta quadrupole resonance

Yasuoka, Hiroshi; Kubo, Tetsuro*; Kishimoto, Yasuki*; Kasinathan, D.*; Schmidt, M.*; Yan, B.*; Zhang, Y.*; To, Hideki*; Felser, C.*; Mackenzie, A. P.*; et al.

Physical Review Letters, 118(23), p.236403_1 - 236403_6, 2017/07

 Times Cited Count:26 Percentile:83.03(Physics, Multidisciplinary)

The $$^{181}$$Ta quadrupole resonance (NQR) technique has been utilized to investigate the microscopic magnetic properties of the Weyl semi-metal TaP. We found three zero-field NQR signals associated with the transition between the quadrupole split levels for Ta with $$I$$=7/2 nuclear spin. A quadrupole coupling constant, $$nu_Q$$ = 19.250 MHz, and an asymmetric parameter of the electric field gradient, $$eta$$= 0.423 were extracted, in good agreement with the theoretical calculations. In order to examine the magnetic excitations, the temperature dependence of the spin lattice relaxation rate (1/$$T_1T$$) has been measured for the $$f_2$$-line ($$pm 5/2 leftrightarrow pm 3/2$$ transition). We found that there exist two regimes with quite different relaxation processes. Above $$T$$*$$approx$$K, a pronounced ($$1/T_1T) propto T^2$$ behavior was found which is attributed to the magnetic excitations at the Weyl nodes with temperature dependent orbital hyperfine coupling. Below $$T$$*, the relaxation is mainly governed by Korringa process with (1/$$T_1T$$) = constant, while we have to include a $$T^{-1/2}$$ type dependence in order to reproduce our experimental data. We show that Ta-NQR is a novel probe for the bulk Weyl fermions and their excitations.

Journal Articles

Prospective features for integration of nuclear forensics capability in national framework

Tamai, Hiroshi; Okubo, Ayako; Kimura, Yoshiki; Shinohara, Nobuo; Tazaki, Makiko; Shimizu, Ryo; Suda, Kazunori; Tomikawa, Hirofumi

Proceedings of INMM 58th Annual Meeting (Internet), 6 Pages, 2017/07

Nuclear forensics is a technical measure to analyse and collate samples of illegally used nuclear materials, etc., to clarify their origins, routes, etc. and contribute to criminal identifications. Close collaboration with police and judicial organizations is essential. The national response framework is being built up with international cooperation. Discussions on promoting technical capability and regional cooperation are presented.

Journal Articles

Technical/institutional prerequisite for nuclear forensics response framework

Tamai, Hiroshi; Okubo, Ayako; Kimura, Yoshiki; Kokaji, Lisa; Shinohara, Nobuo; Tomikawa, Hirofumi

Dai-37-Kai Kaku Busshitsu Kanri Gakkai Nihon Shibu Nenji Taikai Rombunshu (CD-ROM), 8 Pages, 2017/02

Nuclear Forensics capability has been developed under the international collaborations. For its effective function, technical development in analysis of seized nuclear materials as well as the institutional development in comprehensive response framework are required under individual national responsibility. In order to keep the "chain of custody" in the proper operation of sample collection at the event scene, radiological analysis at the laboratory, storage of the samples, and further inspection and trial, close cooperation and information sharing between relevant organisations are essential. IAEA issues the Implementing Guide to provide the model action plan and assists individual national development. International cooperation for the technical improvement and awareness cultivation is promoted. Examples in such national developments will be introduced and prospective technical/institutional prerequisite for nuclear forensics response framework will be studied.

Journal Articles

Secondary sodium fire measures in JSFR

Chikazawa, Yoshitaka; Kato, Atsushi*; Yamamoto, Tomohiko; Kubo, Shigenobu; Ohno, Shuji; Iwasaki, Mikinori*; Hara, Hiroyuki*; Shimakawa, Yoshio*; Sakaba, Hiroshi*

Nuclear Technology, 196(1), p.61 - 73, 2016/10

 Times Cited Count:1 Percentile:10.78(Nuclear Science & Technology)

JSFR adopts double boundary for all sodium components. However, design measures are investigated for the secondary sodium fire inside the reactor building, which might be assumed as design extension conditions (DECs). Candidates of sodium fire measures in the secondary sodium systems such as sodium drain, nitrogen injection, pressure release valve, catch pan and leak sodium drain system have been compared from the view point of safety. Wide range of sodium fires in the steam generator room and air cooler have been analyzed evaluating performances of the candidate sodium fire measures.

Journal Articles

Radiation response of silicon carbide metal-oxide-semiconductor transistors in high dose region

Oshima, Takeshi; Yokoseki, Takashi; Murata, Koichi; Matsuda, Takuma; Mitomo, Satoshi; Abe, Hiroshi; Makino, Takahiro; Onoda, Shinobu; Hijikata, Yasuto*; Tanaka, Yuki*; et al.

Japanese Journal of Applied Physics, 55(1S), p.01AD01_1 - 01AD01_4, 2016/01

 Times Cited Count:12 Percentile:55.22(Physics, Applied)

223 (Records 1-20 displayed on this page)