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Joint environmental radiation survey by JAEA and KAERI around the Fukushima Daiichi Nuclear Power Plant; Performance of mobile gamma-ray spectrometry using backpack and carborne survey platforms

Ji, Y.-Y.*; 越智 康太郎; Hong, S. B.*; 中間 茂雄; 眞田 幸尚; 三上 智

Health Physics, 121(6), p.613 - 620, 2021/12



Catalog of gamma-ray glows during four winter seasons in Japan

和田 有希*; 松本 崇弘*; 榎戸 輝揚*; 中澤 知洋*; 湯浅 孝行*; 古田 禄大*; 米徳 大輔*; 澤野 達哉*; 岡田 豪*; 南戸 秀仁*; et al.

Physical Review Research (Internet), 3(4), p.043117_1 - 043117_31, 2021/12

In 2015 the Gamma-Ray Observation of Winter Thunderstorms (GROWTH) collaboration launched a mapping observation campaign for high-energy atmospheric phenomena related to thunderstorms and lightning discharges. This campaign has developed a detection network of gamma rays with up to 10 radiation monitors installed in Kanazawa and Komatsu cities, Ishikawa Prefecture, Japan, where low-charge-center winter thunderstorms frequently occur. During four winter seasons from October 2016 to April 2020, in total 70 gamma-ray glows, minute-lasting bursts of gamma rays originating from thunderclouds, were detected. Their average duration is 58.9 sec. Among the detected events, 77% were observed in nighttime. The gamma-ray glows can be classified into temporally-symmetric, temporally-asymmetric, and lightning-terminated types based on their count-rate histories. An averaged energy spectrum of the gamma-ray glows is well fitted with a power-law function with an exponential cutoff, whose photon index, cutoff energy, and flux are 0.613 $$pm$$ 0.009, 4.68 $$pm$$ 0.04 MeV, and (1.013 $$pm$$ 0.003) $$times$$ 10$$^{-5}$$ erg cm$$^{-2}$$s$$^{-1}$$ (0.2-20.0 MeV), respectively. The present paper provides the first catalog of gamma-ray glows and their statistical analysis detected during winter thunderstorms in the Kanazawa and Komatsu areas.


Half-integer Shapiro steps in strong ferromagnetic Josephson junctions

Yao, Y.*; Cai, R.*; Yang, S.-H.*; Xing, W.*; Ma, Y.*; 森 道康; Ji, Y.*; 前川 禎通; Xie, X.-C.*; Han, W.*

Physical Review B, 104(10), p.104414_1 - 104414_6, 2021/09

 被引用回数:0 パーセンタイル:0(Materials Science, Multidisciplinary)

We report the experimental observation of half-integer Shapiro steps in the strong ferromagnetic Josephson junction (Nb-NiFe-Nb) by investigating the current-phase relation under radio-frequency microwave excitation. The half-integer Shapiro steps are robust in a wide temperature range from T = 4 to 7 K. The half-integer Shapiro steps could be attributed to co-existence of 0- and $$pi$$-states in the strong ferromagnetic NiFe Josephson junctions with the spatial variation of the NiFe thickness. This scenario is also supported by the high-resolution transmission electron microscopy characterization of the Nb/NiFe/Nb junction.


Evaluation report of Task 9B based on comparisons and analyses of modelling results for the $"A$sp$"o$ HRL LTDE-SD experiments

Soler, J. M.*; Meng, S.*; Moreno, L.*; Neretnieks, I.*; Liu, L.*; Kek$"a$l$"a$inen, P.*; Hokr, M.*; $v{R}$$'i$ha, J.*; Vete$v{s}$n$'i$k, A.*; Reimitz, D.*; et al.

SKB TR-20-17, 71 Pages, 2021/07

亀裂性岩石中の地下水流動と物質移行のモデル化に関するSKBタスクフォースにおけるTask 9Bは、スウェーデンのエスポ岩盤研究所で実施された原位置長期収着・拡散試験(LTDE-SD)の試験結果のモデル化に焦点をあてたものである。10のモデリングチームによって、異なるモデル概念やコードを用いたモデル化が実施された。モデル化のアプローチは、(1)拡散方程式の解析解、(2)連続多孔質媒体中の数値計算モデル、(3)微細な不均質性(鉱物粒界,微細亀裂の分布等)を考慮した微細構造モデルの大きく3種に分類できる。異なるチームによるモデル化結果から、岩石や亀裂の表面の擾乱影響を含む岩石特性の不均質な分布、微細な亀裂の効果など、様々な異なるモデル概念の比較・評価がなされた。


Performance of in situ gamma-ray spectrometry in the assessment of radioactive cesium deposition around the Fukushima Daiichi Nuclear Power Plant

Ji, Y.-Y.*; 越智 康太郎; Hong, S. B.*; 中間 茂雄; 眞田 幸尚; 三上 智

Radiation Physics and Chemistry, 179, p.109205_1 - 109205_11, 2021/02

 被引用回数:1 パーセンタイル:0.01(Chemistry, Physical)

福島第一原子力発電所周辺の異なる線量レベルのエリアで、様々なサーベイプラットフォームを用いin-situ $$gamma$$線スペクトロメトリーを実施した。地表における放射性セシウム沈着量を、高純度Ge半導体検出器とLaBr$$_{3}$$(Ce)検出器を用いて評価するために、福島第一原子力発電所周辺の6か所のサイト(うち2つは帰還困難区域)が選択された。2018年10月に行ったin-situ測定の結果、$$^{137}$$Csの沈着量は6つのサイトで30-3000kBq m$$^{-2}$$の範囲にあった。また、広範囲の代表的な深度分布を直接的に計算するin-situ測定手法を導入し、その結果が同じサイトで採取された土壌サンプルの結果をよく表現していることが分かった。


Production of $$^{266}$$Bh in the $$^{248}$$Cm($$^{23}$$Na,5$$n$$)$$^{266}$$Bh reaction and its decay properties

羽場 宏光*; Fan, F.*; 加治 大哉*; 笠松 良崇*; 菊永 英寿*; 小森 有希子*; 近藤 成美*; 工藤 久昭*; 森本 幸司*; 森田 浩介*; et al.

Physical Review C, 102(2), p.024625_1 - 024625_12, 2020/08

 被引用回数:2 パーセンタイル:57.67(Physics, Nuclear)

The nuclide $$^{266}$$Bh was produced in the $$^{248}$$Cm($$^{23}$$Na,5n)$$^{266}$$Bh reaction at beam energies of 125.9, 130.6, and 135.3 MeV. Decay properties of $$^{266}$$Bh were investigated with a rotating wheel apparatus for $$alpha$$ and spontaneous fission (SF) spectrometry under low background conditions attained by a gas-jet transport system coupled to the RIKEN gas-filled recoil ion separator. The half-life of $$^{266}$$Bh was measured to be $$T_{rm 1/2}$$ = 10.0$$^{+2.6}_{-1.7}$$ s. The $$alpha$$-particle energies of $$^{266}$$Bh disperse widely in the range of 8.62 - 9.40 MeV. The maximum production cross section for the $$^{248}$$Cm($$^{23}$$Na,5n)$$^{266}$$Bh reaction was determined to be $$sigma$$ = 57 $$pm$$ 14 pb at 130.6 MeV.


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.*; 宮本 幸治*; 奥田 太一*; 木村 昭夫*; 黒田 健太*; et al.

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

 被引用回数:13 パーセンタイル:91.8(Multidisciplinary Sciences)

Modification of the gap at the Dirac point (DP) in axion antiferromagnetic topological insulator MnBi$$_{2}$$Te$$_{4}$$ and its electronic and spin structure have been studied by angle- and spin-resolved photoemission spectroscopy (ARPES) under laser excitation at various temperatures, light polarizations and photon energies. We have distinguished both large and reduced gaps at the DP in the ARPES dispersions, which remain open above the N$'{e}$el temperature of $$T_textrm{N}$$ = 24.5 K. We propose that the gap above $$T_textrm{N}$$ remains open due to a short-range magnetic field generated by chiral spin fluctuations. Spin-resolved ARPES, XMCD and circular dichroism ARPES measurements show a surface ferromagnetic ordering for the large gap sample and apparently significantly reduced effective magnetic moment for the reduced gap sample.


High-field depinned phase and planar Hall effect in the skyrmion host Gd$$_2$$PdSi$$_3$$

Hirschberger, M.*; 中島 多朗*; Kriener, M.*; 車地 崇*; Spitz, L.*; Gao, S.*; 吉川 明子*; 山崎 裕一*; 佐賀山 基*; 中尾 裕則*; et al.

Physical Review B, 101(22), p.220401_1 - 220401_6, 2020/06

 被引用回数:12 パーセンタイル:92.16(Materials Science, Multidisciplinary)

For the skyrmion-hosting intermetallic Gd$$_2$$PdSi$$_3$$ with centrosymmetric hexagonal lattice and triangular net of rare earth sites, we report a thorough investigation of the magnetic phase diagram. Our work reveals a magnetic phase with an isotropic value of the critical field for all orientations, where the magnetic ordering vector ${bf q}$ is depinned from its preferred directions in the basal plane. The bulk nature of the skyrmion lattice and of other magnetic phases was evidenced by specific-heat measurements. Resistivity anisotropy, likely originating from partial gapping of the density of states along ${bf q}$ in this Ruderman-Kittel-Kasuya-Yoshida magnet, is picked up via the planar Hall effect (PHE). The PHE confirms the single-${bf q}$ nature of the magnetic order when the field is in the hexagonal plane, and allows one to detect the preferred directions of ${bf q}$. Several scenarios for the depinned phase are discussed on the basis of the data.


Study of quasielastic barrier distributions as a step towards the synthesis of superheavy elements with hot fusion reactions

田中 泰貴*; 森田 浩介*; 森本 幸司*; 加治 大哉*; 羽場 宏光*; Boll, R. A.*; Brewer, N. T.*; Van Cleve, S.*; Dean, D. J.*; 石澤 倫*; et al.

Physical Review Letters, 124(5), p.052502_1 - 052502_6, 2020/02

 被引用回数:4 パーセンタイル:72.03(Physics, Multidisciplinary)

The excitation functions for quasielastic scattering of $$^{22}$$Ne+$$^{248}$$Cm, $$^{26}$$Mg+$$^{248}$$Cm, $$^{48}$$Ca+$$^{238}$$U are measured using a gas-filled recoil ion separator The quasielastic barrier distributions are extracted for these systems and are compared with coupled-channel calculations. The results indicate that the barrier distribution is affected dominantly by deformation of the actinide target nuclei, but also by vibrational or rotational excitations of the projectile nuclei, as well as neutron transfer processes before capture. From a comparison between the experimental barrier distributions and the evaporation residue cross sections for Sg (Z=106), Hs (108), Cn (112), and Lv (116), it is suggested that the hot fusion reactions take advantage of a compact collision, where the projectile approaches along the short axis of a prolately deformed nucleus. A new method is proposed to estimate the optimum incident energy to synthesize unknown superheavy nuclei using the barrier distribution.


Organ and detriment-weighted dose rate coefficients for exposure to radionuclide-contaminated soil considering body morphometries that differ from reference conditions; Adults and children

Kofler, C.*; Domal, S.*; 佐藤 大樹; Dewji, S.*; Eckerman, K.*; Bolch, W. E.*

Radiation and Environmental Biophysics, 58(4), p.477 - 492, 2019/11

 被引用回数:3 パーセンタイル:42.47(Biology)

現行の放射線防護における線量評価では、国際放射線防護委員会(ICRP)が定義する実効線量等を用いる。この実効線量は、ICRPが定義する各年齢の標準体型を模擬する人体模型により計算される臓器吸収線量から導出される。一方、標準体型から逸脱した個人を考慮した線量推定において、標準体型に基づく実効線量の適用の妥当性が議論されてきた。本研究では、標準体型以外の人体模型により、臓器線量を基本として実効線量と同様の手法で導出される損害加重線量を解析した。ここでは、土壌に沈着した放射性核種からの外部被ばく条件に対し、米国立健康統計学センターが報告する身長及び体重を網羅した351体の人体数値模型を適用した。また、ICRPが与える核種崩壊データベースから、33種類の核種を評価対象とした。その結果、環境での外部被ばくで問題となる$$^{89}$$Sr, $$^{90}$$Sr, $$^{137}$$Cs及び$$^{131}$$Iに対して、1歳児の実効線量と損害加重線量は5%以内で一致した。一方、年齢とともに、標準体型からの逸脱による実効線量と損害加重線量の差は大きくなり、成人では+15%から-40%の偏差を持つことが明らかになった。本データは、個人の体格特性に着目する線量再構築や疫学調査における線量推定の精度を向上させるものである。


Q dependence of magnetic resonance mode on FeTe$$_{0.5}$$Se$$_{0.5}$$ studied by inelastic neutron scattering

石角 元志*; 樹神 克明; 梶本 亮一; 中村 充孝; 稲村 泰弘; 池内 和彦*; Ji, S.*; 新井 正敏*; 社本 真一

Condensed Matter (Internet), 4(3), p.69_1 - 69_10, 2019/09



Nature of dynamic ferrite transformation revealed by ${it in-situ}$ neutron diffraction analysis during thermomechanical processing

柴田 曉伸*; 竹田 泰成*; Park, N.*; Zhao, L.*; Harjo, S.; 川崎 卓郎; Gong, W.*; 辻 伸泰*

Scripta Materialia, 165, p.44 - 49, 2019/05

 被引用回数:15 パーセンタイル:88.34(Nanoscience & Nanotechnology)

Nowadays, a new concept of process utilizing dynamic ferrite transformation, which can achieve ultrafine-grained structure with a mean grain size of approximately 1$$mu$$m, has been proposed. This paper reports transformation mode of dynamic ferrite transformation and formation mechanism of ultrafine-grained structure revealed by our novel technique of ${it in-situ}$ neutron diffraction analysis during thermomechanical processing. Dynamic ferrite transformation occurs in a diffusional manner, whose partitioning behavior changes from para- to ortho-equilibrium with the progress of transformation. Moreover, we propose that dynamic recrystallization of dynamically-transformed ferrite is the main mechanism for the formation of ultrafine-grained structure.


Evaluation and modelling report of Task 9A based on comparisons and analyses of predictive modelling results for the REPRO WPDE experiments; Task 9 of SKB Task Force GWFTS - Increasing the realism in solute transport modelling based on the field experiments REPRO and LTDE-SD

Soler, J. M.*; Neretnieks, I.*; Moreno, L.*; Liu, L.*; Meng, S.*; Svensson, U.*; Trinchero, P.*; Iraola, A.*; Ebrahimi, H.*; Molinero, J.*; et al.

SKB R-17-10, 153 Pages, 2019/01



Magnetic excitations in the orbital disordered phase of MnV$$_2$$O$$_4$$

松浦 慧介*; 佐賀山 基*; 上原 周*; 新居 陽一*; 梶本 亮一; 蒲沢 和也*; 池内 和彦*; Ji, S.*; 阿部 伸行*; 有馬 孝尚*

Physica B; Condensed Matter, 536, p.372 - 376, 2018/05

 被引用回数:2 パーセンタイル:16.65(Physics, Condensed Matter)

We have investigated the temperature dependence of magnetic dynamics in a spinel-type vanadium oxide MnV$$_2$$O$$_4$$ by inelastic neutron scattering. The scattering intensity of excitation around 20 meV disappears in the collinear intermediate-temperature cubic-ferrimagnetic phase, which reveals that this excitation should be peculiar to the orbital ordered phase. We have found a weakly dispersive mode emergent from a non-integer wavevector $$(1.4,1.4,0)$$ at 56 K, which lies in the cubic-ferrimagnetic phase between non-coplanar ferrimagnetic and paramagnetic phases. This indicates that the probable presence of an incommensurate instability in the simple collinear structure.


In situ neutron diffraction study on microstructure evolution during thermo-mechanical processing of medium manganese steel

中村 良彦*; 柴田 曉伸*; Gong, W.*; Harjo, S.; 川崎 卓郎; 伊東 篤志*; 辻 伸泰*

Proceedings of International Conference on Martensitic Transformations: Chicago, p.155 - 158, 2018/04

The microstructure evolution of medium manganese steel (Fe-5Mn-2Si-0.1C (wt%)) during thermo-mechanical processing in ferrite + austenite two-phase region was investigated by in situ neutron diffraction analysis and microstructure observations. When the specimens were isothermally held at a temperature of 700$$^circ$$C, the fraction of reversely transformed austenite increased gradually with an increase in the isothermal holding time. However, it did not reach the equilibrium fraction of austenite even after isothermal holding for 10 ks. On the other hand, the fraction of reversely transformed austenite increased rapidly after the compressive deformation at a strain rate of 1 s$$^{-1}$$ at 700$$^circ$$C and reached the equilibrium state during subsequent isothermal holding for around 3 ks.


$$beta$$-delayed fission of $$^{230}$$Am

Wilson, G. L.*; 武山 美麗*; Andreyev, A.; Andel, B.*; Antalic, S.*; Catford, W. N.*; Ghys, L.*; 羽場 宏光*; He${ss}$berger, F. P.*; Huang, M.*; et al.

Physical Review C, 96(4), p.044315_1 - 044315_7, 2017/10

 被引用回数:5 パーセンタイル:51.78(Physics, Nuclear)

The exotic decay process of $$beta$$-delayed fission has been studied in the neutron-deficient isotope $$^{230}$$Am at RIKEN, Japan. The $$^{230}$$Am nuclei were produced in the complete fusion reaction $$^{207}$$Pb($$^{27}$$Al,4n)$$^{230}$$Am and separated by using the GARIS gas-filled recoil ion separator. A lower limit for the $$beta$$-delayed fission probability larger than 0.30 was deduced, which so far is the highest value among all known nuclei exhibiting this decay mode.


Magnetic properties of electron-doped LaCoO$$_3$$

富安 啓輔*; 佐藤 美嘉*; 小山 俊一*; 野島 勉*; 梶本 亮一; Ji, S.*; 岩佐 和晃*

Journal of the Physical Society of Japan, 86(9), p.094706_1 - 094706_6, 2017/09

 被引用回数:0 パーセンタイル:0(Physics, Multidisciplinary)

We studied electron-doped LaCo$$_{1-y}$$Te$$^{6+}_{y}$$O$$_{3}$$ by magnetization measurements and neutron scattering. The effective Bohr magneton, estimated in the Curie-Weiss fitting around room temperature, is independent of $$y$$. This suggests that magnetic Co$$^{3+mathrm{(HS)}}$$, not nonmagnetic Co$$^{3+mathrm{(LS)}}$$, is mainly replaced by doped magnetic Co$$^{2+mathrm{(HS)}}$$. At the lowest temperatures, a Brillouin-function-like saturating behavior persists in the magnetization curves even in the high-$$y$$ samples, and neither clear magnetic reflection nor magnetic dispersion is observed by neutron scattering. These indicate that magnetic correlation is very weak in contrast to the well-known hole-doped LaCoO$$_3$$ accompanied with the transition to ferromagnetic metal. However, we also found that the low-$$y$$ samples exhibit nonnegligible enhancement in saturated magnetization by $$sim$$2 $$mu_B$$/doped-electron. All these characteristics are discussed in the light of activation and inactivation of spin-state blockade.


Spin-orbital correlated dynamics in the spinel-type vanadium oxide MnV$$_{2}$$O$$_{4}$$

松浦 慧介*; 佐賀山 基*; 上原 周*; 新居 陽一*; 梶本 亮一; 蒲沢 和也*; 池内 和彦*; Ji, S.*; 阿部 伸行*; 有馬 孝尚*

Physical Review Letters, 119(1), p.017201_1 - 017201_6, 2017/07

 被引用回数:8 パーセンタイル:63.32(Physics, Multidisciplinary)

We investigate the magnetic dynamics in the spinel-type vanadium oxide MnV$$_2$$O$$_4$$. Inelastic neutron scattering around 10 meV and a Heisenberg model analysis have revealed that V$$^{3+}$$ spin-wave modes exist at a lower-energy region than previously reported. The scattering around 20 meV cannot be reproduced with the spin-wave analysis. We propose that this scattering could originate from the spin-orbital coupled excitation. This scattering is most likely attributable to V$$^{3+}$$ spin-wave modes, entangled with the orbital hybridization between $$t_{2g}$$ orbitals.


Study of the reaction $$^{48}$$Ca + $$^{248}$$Cm $$rightarrow$$ $$^{296}$$Lv$$^{ast}$$ at RIKEN-GARIS

加治 大哉*; 森田 浩介*; 森本 幸司*; 羽場 宏光*; 浅井 雅人; 藤田 訓裕*; Gan, Z.*; Geissel, H.*; 長谷部 裕雄*; Hofmann, S.*; et al.

Journal of the Physical Society of Japan, 86(3), p.034201_1 - 034201_7, 2017/03

 被引用回数:16 パーセンタイル:79.57(Physics, Multidisciplinary)

理化学研究所のガス充填型反跳核分離装置GARISを用いて$$^{48}$$Ca + $$^{248}$$Cm $$rightarrow$$ $$^{296}$$Lv$$^{ast}$$融合反応を調べた。116番元素$$^{292}$$Lv, $$^{293}$$Lvと思われる核反応生成物に起因するアルファ線と自発核分裂の崩壊連鎖が7事象観測された。崩壊連鎖中に観測された原子核の性質は過去の報告値とよく一致したが、1つの崩壊連鎖で一部矛盾が観測された。これは$$^{285}$$Cnの新しい自発核分裂分岐比の存在、あるいは新同位体$$^{294}$$Lv生成の可能性を示唆するものと思われる。


Development of CdTe pixel detectors combined with an aluminum Schottky diode sensor and photon-counting ASICs

豊川 秀訓*; 佐治 超爾*; 川瀬 守弘*; Wu, S.*; 古川 行人*; 梶原 堅太郎*; 佐藤 真直*; 広野 等子*; 城 鮎美*; 菖蒲 敬久; et al.

Journal of Instrumentation (Internet), 12(1), p.C01044_1 - C01044_7, 2017/01

 被引用回数:2 パーセンタイル:15.8(Instruments & Instrumentation)

アルミニウムショットキーダイオードセンサとフォトンカウンティングASICsを組み合わせたCdTeピクセル検出器の開発を行っている。このハイブリッドピクセル検出器は、200マイクロメートル$$times$$200マイクロメートルのピクセルサイズで、19ミリメートル$$times$$20ミリメートルまたは38.2ミリメートル$$times$$40.2ミリメートルの面積で設計された。フォトンカウンティングASIC SP8-04F10Kは、プリアンプ,シェーパ, 3レベルのウィンドウタイプのディスクリミネータ、および各ピクセルが24ビットカウンタを備えている。そしてウィンドウコンパレータを用いてX線エネルギーを選択するフォトンカウンティングモードで精密に動作し、100$$times$$95ピクセルのシングルチップ検出器が20$$^{circ}$$Cで実現している。本研究では、本検出器の性能を評価するため、白色X線マイクロビーム実験のフィージビリティスタディを行った。珪素鋼試料に白色X線を照射し、照射位置を走査しながらラウエ回折を測定した。その結果、各位置で隣接する画像間の差を用いることで試料内の粒界の観察に成功した。

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