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Journal Articles

Nature of the Dirac gap modulation and surface magnetic interaction in axion antiferromagnetic topological insulator MnBi$$_{2}$$Te$$_{4}$$

Shikin, A. M.*; Estyunin, D. A.*; Klimovskikh, I. I.*; Filnov, S. O.*; Kumar, S.*; Schwier, E. F.*; Miyamoto, Koji*; Okuda, Taiichi*; Kimura, Akio*; Kuroda, Kenta*; et al.

Scientific Reports (Internet), 10, p.13226_1 - 13226_13, 2020/08

Journal Articles

Crystal and magnetic structures of double hexagonal close-packed iron deuteride

Saito, Hiroyuki*; Machida, Akihiko*; Iizuka, Riko*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Sato, Toyoto*; Orimo, Shinichi*; Aoki, Katsutoshi*

Scientific Reports (Internet), 10, p.9934_1 - 9934_8, 2020/06

 Times Cited Count:0 Percentile:100(Multidisciplinary Sciences)

Neutron powder diffraction profiles were collected for iron deuteride (FeDx) while the temperature decreased from 1023 to 300 K for a pressure range of 4-6 GPa. The $$varepsilon$$' deuteride with a double hexagonal close-packed (dhcp) structure, which coexisted with other stable or metastable deutrides at each temperature and pressure condition, formed solid solutions with a composition of FeD$$_{0.68(1)}$$ at 673 K and 6.1 GPa and FeD$$_{0.74(1)}$$ at 603 K and 4.8 GPa. Upon stepwise cooling to 300 K, the D-content x increased to a stoichiometric value of 1.0 to form monodeuteride FeD$$_{1.0}$$. In the dhcp FeD$$_{1.0}$$ at 300 K and 4.2 GPa, dissolved D atoms fully occupied the octahedral interstitial sites, slightly displaced from the octahedral centers in the dhcp metal lattice, and the dhcp sequence of close-packed Fe planes contained hcp-stacking faults at 12%. Magnetic moments with 2.11 $$pm$$ 0.06 B/Fe-atom aligned ferromagnetically in parallel on the Fe planes.

Journal Articles

Hydrogen-accelerated spontaneous microcracking in high-strength aluminium alloys

Tsuru, Tomohito; Shimizu, Kazuyuki*; Yamaguchi, Masatake; Itakura, Mitsuhiro; Ebihara, Kenichi; Bendo, A.*; Matsuda, Kenji*; Toda, Hiroyuki*

Scientific Reports (Internet), 10, p.1998_1 - 1998_8, 2020/04

 Times Cited Count:1

Age-hardening has been one and only process to achieve high strength aluminum alloys since unlike iron and titanium, pure aluminum does not have other solid phases during heat treatment. Highly-concentrated precipitations play therefore dominant role in mechanical properties and hydrogen embrittlement of aluminium alloys. It has been considered that the coherent interface between matrix and precipitation does not contribute to the crack initiation and embrittlement due to its coherency. Here, we discovered the origin of unprecedented quasi-cleavage fracture mode. Hydrogen partitioning at various defect sites is investigated comprehensively combined with experiment, theory and first-principles calculations. We demonstrate that despite low excess free volume, the aluminum-precipitation interface is more preferable trap site than void and grain boundary. The cohesivity of the interface deteriorates significantly with increasing occupancy while hydrogen atoms are trapped stably up to extremely high occupancy equivalent to spontaneous cleavage.

Journal Articles

Effectiveness of decontamination by litter removal in Japanese forest ecosystems affected by the Fukushima nuclear accident

Koarashi, Jun; Atarashi-Andoh, Mariko; Nishimura, Shusaku; Muto, Kotomi*

Scientific Reports (Internet), 10(1), p.6614_1 - 6614_11, 2020/04

 Times Cited Count:0 Percentile:100(Multidisciplinary Sciences)

We conducted a pilot-scale decontamination study in a deciduous broadleaved forest in Fukushima. The entire forest, other than two untreated areas, was decontaminated by removing the litter layer approximately 3.3 years after the accident. For three years after decontamination, we quantified $$^{137}$$Cs contamination levels in the litter and topsoil layers and in the tree leaves, in the untreated and decontaminated areas. The decreased inventories of litter-associated $$^{137}$$Cs in the decontaminated areas were observed only in the first year after decontamination. Generally, no decontamination effects were observed on the $$^{137}$$Cs transfer in tree leaves. The primary reason for this was the rapid shift in the main reservoir of $$^{137}$$Cs from litter layers to the underlying mineral soil, which differs from the observations in post-Chernobyl studies of European forest ecosystems. The results suggest that litter-removal decontamination can only be successful if it is implemented more quickly for Japanese forest ecosystems.

Journal Articles

Initial decrease in the ambient dose equivalent rate after the Fukushima accident and its difference from Chernobyl

Yoshimura, Kazuya; Saegusa, Jun; Sanada, Yukihisa

Scientific Reports (Internet), 10(1), p.3859_1 - 3859_9, 2020/03

 Times Cited Count:1

Journal Articles

Reconstruction of residents' thyroid equivalent doses from internal radionuclides after the Fukushima Daiichi Nuclear Power Station accident

Oba, Takashi*; Ishikawa, Tetsuo*; Nagai, Haruyasu; Tokonami, Shinji*; Hasegawa, Arifumi*; Suzuki, Gen*

Scientific Reports (Internet), 10(1), p.3639_1 - 3639_11, 2020/02

 Times Cited Count:1

Internal doses of residents after the Fukushima Daiichi Nuclear Power Station accident have been reconstructed. In total 896 behaviour records in the Fukushima Health Management Survey were analysed to estimate thyroid doses via inhalation, using a spatiotemporal radionuclides concentration database constructed by atmospheric dispersion simulations. After a decontamination factor for sheltering and a modifying factor for the dose coefficient were applied, estimated thyroid doses were close to those estimated on the basis of direct thyroid measurement. The median and 95th percentile of thyroid doses of 1-year-old children ranged from 1.2 to 15 mSv and from 7.5 to 30 mSv, respectively.

Journal Articles

Compositional and structural analysis of Fukushima-derived particulates using high-resolution X-ray imaging and synchrotron characterisation techniques

Martin, P. G.*; Jones, C. P.*; Cipiccia, S.*; Batey, D. J.*; Hallam, K. R.*; Satou, Yukihiko; Griffiths, I.*; Rau, C.*; Richards, D. A.*; Sueki, Keisuke*; et al.

Scientific Reports (Internet), 10(1), p.1636_1 - 1636_11, 2020/01

 Times Cited Count:1

Journal Articles

Stacking fault energy analyses of additively manufactured stainless steel 316L and CrCoNi medium entropy alloy using in situ neutron diffraction

Woo, W.*; Jeong, J. S.*; Kim, D.-K.*; Lee, C. M.*; Choi, S.-H.*; Suh, J.-Y.*; Lee, S. Y.*; Harjo, S.; Kawasaki, Takuro

Scientific Reports (Internet), 10(1), p.1350_1 - 1350_15, 2020/01

 Times Cited Count:0

Journal Articles

Track structure study for energy dependency of electrons and X-rays on DNA double-strand break induction

Yachi, Yoshie*; Yoshii, Yuji*; Matsuya, Yusuke; Mori, Ryosuke*; Oikawa, Joma*; Date, Hiroyuki*

Scientific Reports (Internet), 9(1), p.17649_1 - 17649_8, 2019/11

 Times Cited Count:1 Percentile:62.18(Multidisciplinary Sciences)

Radiation weighting factor for photon and electron is defined as 1.0 independently these energies. However, it should be noted that the biological effects after 29 kVp X-rays is relative higher than standard 200 kVp X-rays at the endpoint of ${it in vitro}$. And it is of importance to evaluate electrons generated via interaction of photons with matter. Here, we evaluated the energy concentration along electron track (dose-mean lineal energy) on chromosome (micron-meter) scales by Monte Carlo simulation, and measured the DNA double-strand breaks (DSBs) induction. From the cell experiments, the DSBs induction after diagnostic X-rays exposure (60-100 kVp) is higher than those with therapeutic X-rays (6 MV). In the relation between the dose-mean lineal energy and the number of DSBs, it was shown that lower energy photons might induce more biological impact due to the interaction by low energy electron. This study implies that radiation weighting factor for photon and electron should not be unity.

Journal Articles

Hexagonal close-packed iron hydride behind the conventional phase diagram

Machida, Akihiko*; Saito, Hiroyuki*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Sato, Toyoto*; Orimo, Shinichi*; Aoki, Katsutoshi*

Scientific Reports (Internet), 9(1), p.12290_1 - 12290_9, 2019/08

 Times Cited Count:3 Percentile:29.04(Multidisciplinary Sciences)

Hexagonal close-packed iron hydride, hcp FeHx, is absent from the conventional phase diagram of the Fe-H system, although hcp metallic Fe exists stably over extensive temperature ($$T$$) and pressure ($$P$$) conditions, including those corresponding to the Earth's inner core. ${{it In situ}}$ X-ray and neutron diffraction measurements at temperatures ranging from 298 to 1073 K and H pressures ranging from 4 to 7 GPa revealed that the hcp hydride was formed for FeH$$_{x}$$ compositions when $$x < 0.6$$. Hydrogen atoms occupied the octahedral interstitial sites of the host metal lattice both partially and randomly. The hcp hydride exhibited a H-induced volume expansion of 2.48(5) $AA $^{3}$$/H-atom, which was larger than that of the face-centered cubic (fcc) hydride. The hcp hydride showed an increase in $$x$$ with $$T$$, whereas the fcc hydride showed a corresponding decrease. The present study provides guidance for further investigations of the Fe-H system over an extensive $$x$$-$$T$$-$$P$$ region.

Journal Articles

First determination of Pu isotopes ($$^{239}$$Pu, $$^{240}$$Pu and $$^{241}$$Pu) in radioactive particles derived from Fukushima Daiichi Nuclear Power Plant accident

Igarashi, Junya*; Zheng, J.*; Zhang, Z.*; Ninomiya, Kazuhiko*; Satou, Yukihiko; Fukuda, Miho*; Ni, Y.*; Aono, Tatsuo*; Shinohara, Atsushi*

Scientific Reports (Internet), 9(1), p.11807_1 - 11807_10, 2019/08

 Times Cited Count:2 Percentile:52.23(Multidisciplinary Sciences)

Radioactive particles were released into the environment during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Many studies have been conducted to elucidate the chemical composition of released radioactive particles in order to understand their formation process. However, whether radioactive particles contain nuclear fuel radionuclides remains to be investigated. Here, we report the first determination of Pu isotopes in radioactive particles. To determine the Pu isotopes ($$^{239}$$Pu, $$^{240}$$Pu and $$^{241}$$Pu) in radioactive particles derived from the FDNPP accident which were free from the influence of global fallout, radiochemical analysis and inductively coupled plasma-mass spectrometry measurements were conducted. Radioactive particles derived from unit 1 and unit 2 or 3 were analyzed. For the radioactive particles derived from unit 1, activities of $$^{239+240}$$Pu and $$^{241}$$Pu were (1.70-7.06)$$times$$10$$^{-5}$$ Bq and (4.10-8.10)$$times$$10$$^{-3}$$ Bq, respectively and atom ratios of $$^{240}$$Pu/$$^{239}$$Pu and $$^{241}$$Pu/$$^{239}$$Pu were 0.330-0.415 and 0.162-0.178, respectively. These ratios were consistent with the simulation results from ORIGEN code and measurements from various environmental samples. In contrast, Pu was not detected in the radioactive particles derived from unit 2 or 3. The difference in Pu contents is clear evidence towards different formation processes of radioactive particles, and detailed formation processes can be investigated from Pu analysis.

Journal Articles

Intensity modulated radiation fields induce protective effects and reduce importance of dose-rate effects

Matsuya, Yusuke; McMahon, S. J.*; Ghita, M.*; Yoshii, Yuji*; Sato, Tatsuhiko; Date, Hiroyuki*; Prise, K. M.*

Scientific Reports (Internet), 9(1), p.9483_1 - 9483_12, 2019/07

 Times Cited Count:3 Percentile:26.73(Multidisciplinary Sciences)

In radiotherapy, intensity modulated radiation fields and complex dose-delivery are used to prescribe doses to tumors. Here, we analyzed the impact of modulated field on radio-sensitivity and cell recovery during irradiation time. The dose was delivered to either 50% of the area of the flask containing cells (half-field) or 100% of the flask (uniform-field). We also modelled cell-killing considering dose-rate effects and intercellular signals. It is found that (i) in-field cell survival under half-field exposure is higher than uniform-field exposure even with the same dose; (ii) the importance of sub-lethal damage repair in normal human skin fibroblast cells under the half-field is reduced; (iii) the increase of cell survival under half-field is predominantly attributed to not rescue effects (increased repair) but protective effects (reduced initial DNA lesion yield). These findings provide new understanding of radio-sensitivity for hit and non-hit cells under non-uniform exposure.

Journal Articles

DNA damage induction during localized chronic exposure to an insoluble radioactive microparticle

Matsuya, Yusuke; Satou, Yukihiko; Hamada, Nobuyuki*; Date, Hiroyuki*; Ishikawa, Masayori*; Sato, Tatsuhiko

Scientific Reports (Internet), 9(1), p.10365_1 - 10365_9, 2019/07

 Times Cited Count:2 Percentile:40(Multidisciplinary Sciences)

Insoluble radioactive microparticles (so called Cs-bearing particles) have been assumed to adhere in the long term to trachea after aspirated into respiratory system, leading to heterogeneous dose distribution within healthy tissue around the particles. The biological effects posed by such a particle remain unclear. Here, we show cumulative DNA damage in cultured cells proximal and distal to the particle under localized chronic exposure in comparison with uniform exposure. We placed the particle-contained microcapillary onto a glass-base dish containing normal human lung cells in vitro, and observed a significant change in nuclear $$gamma$$-H2AX foci after 24 h or 48 h exposure to the particle. The dose calculation by a Monte Carlo simulation and the comparison with nuclear foci under uniform exposure suggested that the localized exposure to a Cs-bearing particle leads to not only signal-induced DNA damage to distal cells but also the reduction of DNA damage induction yield to proximal cells (protective effects). Considering the small organ dose, the conventional radiation risk assessment is adequate. This study is the first to quantify the spatial distribution of cumulative DNA lesions under heterogeneous exposure by insoluble Cs-bearing particles.

Journal Articles

A New perspective on the $$^{137}$$Cs retention mechanism in surface soils during the early stage after the Fukushima nuclear accident

Koarashi, Jun; Nishimura, Shusaku; Atarashi-Andoh, Mariko; Muto, Kotomi; Matsunaga, Takeshi*

Scientific Reports (Internet), 9, p.7034_1 - 7034_10, 2019/05

 Times Cited Count:11 Percentile:9.01(Multidisciplinary Sciences)

The aim of the present study is to explore the retention mechanisms of $$^{137}$$Cs in the surface soil layers of terrestrial ecosystems affected by the Fukushima NPP accident, with a specific focus on the interactions between $$^{137}$$Cs, soil minerals, and organic matter. Soil samples were collected from field, orchard, and forest sites in July 2011, separated into three soil fractions with different mineral-organic interaction characteristics. The results show that 20-71% of the $$^{137}$$Cs was retained in association with relatively mineral-free, particulate organic matter-dominant fractions in the orchard and forest surface soil layers. Given the physicochemical and mineralogical properties and the $$^{137}$$Cs extractability of the soils, $$^{137}$$Cs incorporation into the complex structure of particulate organic matter is likely the main mechanism for $$^{137}$$Cs retention in the surface soil layers.

Journal Articles

Interstitial hydrogen atoms in face-centered cubic iron in the Earth's core

Ikuta, Daijo*; Otani, Eiji*; Sano, Asami; Shibazaki, Yuki*; Terasaki, Hidenori*; Yuan, L.*; Hattori, Takanori

Scientific Reports (Internet), 9, p.7108_1 - 7108_8, 2019/05

 Times Cited Count:6 Percentile:13.56(Multidisciplinary Sciences)

Hydrogen is likely one of the light elements in the Earth's core. Despite its importance, no direct observation has been made of hydrogen in an iron lattice at high pressure. We made the first direct determination of site occupancy and volume of interstitial hydrogen in a face-centered cubic (fcc) iron lattice up to 12 GPa and 1200 K using the in situ neutron diffraction method. At pressures $$<$$ 5 GPa, the hydrogen content in the fcc iron hydride lattice (x) was small at x $$<$$ 0.3, but increased to x $$>$$ 0.8 with increasing pressure. Hydrogen atoms occupy both octahedral (O) and tetrahedral (T) sites; typically 0.870 in O-sites and 0.057 in T-sites at 12 GPa and 1200 K. The fcc lattice expanded approximately linearly at a rate of 2.22 $AA $^{3}$$ per hydrogen atom, which is higher than previously estimated (1.9 $AA $^{3}$$/H). The lattice expansion by hydrogen dissolution was negligibly dependent on pressure. The large lattice expansion by interstitial hydrogen reduced the estimated hydrogen content in the Earth's core that accounted for the density deficit of the core. The revised analyses indicate that whole core may contain hydrogen of 80 times of the ocean mass with 79 and 0.8 ocean mass for the outer and inner cores, respectively.

Journal Articles

Dissolution behaviour of radiocaesium-bearing microparticles released from the Fukushima nuclear plant

Okumura, Taiga*; Yamaguchi, Noriko*; Dohi, Terumi; Iijima, Kazuki; Kogure, Toshihiro*

Scientific Reports (Internet), 9(1), p.3520_1 - 3520_9, 2019/03

 Times Cited Count:9 Percentile:13.82(Multidisciplinary Sciences)

Radiocesium-bearing microparticles (CsMPs) were released by the FDNPP accident. We conducted dissolution experiments of CsMPs by reaction with pure water absorbing CO $$_{2}$$ from the atmosphere and seawater. The activation energy for the dissolution of CsMPs was estimated to be 67 and 89 kJ/mol, and the dissolution rate at 13$$^{circ}$$C was 0.011 and 0.130 $$mu$$m/y for pure water and seawater, respectively. Probably the faster dissolution rate in seawater than in pure water is mainly owing to the difference in pH. The shapes of CsMPs dissolved in pure water were considerably altered. Tin oxide and iron oxide nanoparticulates were formed on their surfaces. Such features were similar to those observed in a CsMP collected recently in Fukushima Prefecture, indicating that dissolution of CsMPs is also occurring in the environment. In the case of CsMPs dissolved in seawater, a crust of secondary minerals rich in Mg and Fe was formed and the glass matrix became smaller inside the crust.

Journal Articles

Dirac gap opening and Dirac-fermion-mediated magnetic coupling in antiferromagnetic Gd-doped topological insulators and their manipulation by synchrotron radiation

Shikin, A. M.*; Estyunin, D. A.*; Surnin, Yu. I.*; Koroleva, A. V.*; Shevchenko, E. V.*; Kokh, K. A.*; Tereshchenko, O. E.*; Kumar, S.*; Schwier, E. F.*; Shimada, Kenya*; et al.

Scientific Reports (Internet), 9(1), p.4813_1 - 4813_17, 2019/03

 Times Cited Count:4 Percentile:50.59(Multidisciplinary Sciences)

Journal Articles

Quantum magnetisms in uniform triangular lattices Li$$_{2}$$$$A$$Mo$$_{3}$$O$$_{8}$$ ($$A$$ = In, Sc)

Iida, Kazuki*; Yoshida, Hiroyuki*; Okabe, Hirotaka*; Katayama, Naoyuki*; Ishii, Yuto*; Koda, Akihiro*; Inamura, Yasuhiro; Murai, Naoki; Ishikado, Motoyuki*; Kadono, Ryosuke*; et al.

Scientific Reports (Internet), 9(1), p.1826_1 - 1826_9, 2019/02

 Times Cited Count:1 Percentile:60.52(Multidisciplinary Sciences)

Journal Articles

Detection of alpha particle emitters originating from nuclear fuel inside reactor building of Fukushima Daiichi Nuclear Power Plant

Morishita, Yuki; Torii, Tatsuo; Usami, Hiroshi; Kikuchi, Hiroyuki*; Utsugi, Wataru*; Takahira, Shiro*

Scientific Reports (Internet), 9, p.581_1 - 581_14, 2019/01

 Times Cited Count:3 Percentile:28.85(Multidisciplinary Sciences)

Journal Articles

High-energy spin fluctuation in low-T$$_{c}$$ iron-based superconductor LaFePO$$_{0.9}$$

Ishikado, Motoyuki*; Shamoto, Shinichi; Kodama, Katsuaki; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Hong, T.*; Mutka, H.*

Scientific Reports (Internet), 8, p.16343_1 - 16343_6, 2018/11

 Times Cited Count:2 Percentile:75.88(Multidisciplinary Sciences)

Spin fluctuations are widely believed to play an important role as one of the most possible mechanisms for unconventional high-temperature superconductors. Here, the spin fluctuation in LaFePO$$_{0.9}$$ is found at high energies such as 30-50 meV with comparable intensity to an optimally doped LaFeAs(O,F).

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