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和田 有希*; Wu, T.*; Wang, D.*; 榎戸 輝揚*; 中澤 知洋*; 森本 健志*; 中村 佳敬*; 篠田 太郎*; 土屋 晴文
Journal of Geophysical Research; Atmospheres, 128(15), p.e2023JD038606_1 - e2023JD038606_9, 2023/08
被引用回数：2 パーセンタイル：58.15(Meteorology & Atmospheric Sciences)A gamma-ray glow, a minute-lasting burst of high-energy photons from a thundercloud, was detected by ground-based apparatus at Kanazawa University, Japan, in a winter thunderstorm on 18 December 2018. The gamma-ray glow was quenched by a lightning flash within a brief time window of 40 ms. The lightning flash produced several low-frequency (LF) E-change pulses that were temporally coincident withthe termination of the gamma-ray glow, and that were located within 0.5 km from the observation site by the Fast Antenna Lightning Mapping Array. The LF pulses had the same polarity as a positive cloud-to-ground current and a normal-polarity in-cloud current. Since this polarity is against the upward electric field for producing the gamma-ray glow (accelerating electrons to the ground), we infer that the glow was terminated by a normal-polarity in-cloud discharge activity between a middle negative layer and an upper positive layer.
鶴見 美和*; 榎戸 輝掲*; 一方井 祐子*; Wu, T.*; Wang, D.*; 篠田 太郎*; 中澤 知洋*; 辻 直樹*; Diniz, G.*; 片岡 淳*; et al.
Geophysical Research Letters, 50(13), p.e2023GL103612_1 - e2023GL103612_9, 2023/07
被引用回数：0 パーセンタイル：0(Geosciences, Multidisciplinary)Gamma-ray glows are observational evidence of relativistic electron acceleration due to the electric field in thunderclouds. However, it is yet to be understood whether such relativistic electrons contribute to the initiation of lightning discharges. To tackle this question, we started the citizen science "Thundercloud Project," where we map radiation measurements of glows from winter thunderclouds along Japan's sea coast area. We developed and deployed 58 compact gamma-ray monitors at the end of 2021. On 30 December 2021, five monitors simultaneously detected a glow with its radiation distribution horizontally extending for 2 km. The glow terminated coinciding with a lightning flash at 04:08:34 JST, which was recorded by the two radio-band lightning mapping systems, FALMA and DALMA. The initial discharges during the preliminary breakdown started above the glow, that is, in vicinity of the electron acceleration site. This result provides one example of possible connections between electron acceleration and lightning initiation.
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 
0.009, 4.68 0.04 MeV, and (1.013 0.003) 
10
erg cm
s
(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.
久富 章平*; 中澤 知洋*; 和田 有希*; 辻 結菜*; 榎戸 輝揚*; 篠田 太郎*; 森本 健志*; 中村 佳敬*; 湯浅 孝行*; 土屋 晴文
Journal of Geophysical Research; Atmospheres, 126(18), p.e2021JD034543_1 - e2021JD034543_12, 2021/09
被引用回数：15 パーセンタイル：80.71(Meteorology & Atmospheric Sciences)Around 17:00 on January 12, 2020 (UTC), radiation detectors installed at two locations with a 1.35 km separation in Kanazawa City, Japan, captured a total of four gamma-ray enhancements. The first pair was simultaneously observed at the two locations at 17:03 and were abruptly terminated by a lightning discharge. The remaining two enhancements were also nearly simultaneously observed 
3 min later, and one of them was also terminated by another lightning discharge. At the last termination, a downward terrestrial gamma-ray flash and a negative energetic in-cloud pulse were observed. Both pairs were associated with thundercloud cells. In the first pair, simultaneous detection in two locations 1.35 km apart suggests either a gamma-ray glow emerged in-between and time variability of its intensity were directly observed or there were two (or more) gamma-ray glows in the cell which reached the two detectors coincidentally. In the latter pair, the peak time in the downwind detector was 40 s later than that of the upwind detector. If the irradiation region moved with the cell, it would have taken 110 s. The discrepancy suggests either the glow moved 2.5 times faster than the cell or there were two (or more) glows in the cell. Also, the fact that the thunderstorm cell hosting the latter glows experienced the lightning discharge 3 min before suggests that the strong electric field in the cell can develop within a few minutes.
土屋 晴文; 榎戸 輝揚*; 和田 有希*; 古田 禄大; 中澤 知洋*; 湯浅 孝行*; 楳本 大悟*; 牧島 一夫*; GROWTH Collaboration*
Proceedings of Science (Internet), 358, p.1163_1 - 1163_6, 2021/07
Since 2006, the GROWTH experiment has been successfully operating at the coastal area of Japan Sea. The GROWTH experiment aims at elucidating how particles in lightning and thunderclouds are accelerated to relativistic energies to produce gamma rays and occasionally neutrons. According to observations done by the GROWTH experiment, it is found that there are two types of radiation bursts associated with winter thunderstorms. One is long bursts lasting for a few tens of seconds to a few minutes, being not clearly related to lightning. The other is short bursts in association with lightning. To better understand the production mechanism of these radiation bursts, we have developed a small-type of radiation detectors and increased observational points with the new detectors. In this presentation, we show an overview of observations done by the GROWTH experiment. Then we focus on recent several findings observed by the new detectors. One, which is categorized into long bursts, implies a relationship between a long burst and an intra/inter-cloud discharge. Another is a combination of short bursts and long ones, showing simultaneous detections of prompt gamma rays extending up to 10 MeV and the 511-keV annihilation ones. These gamma-ray signals demonstrate the occurrence of photonuclear reactions in lightning. Based on these results, we discuss the production mechanism of gamma rays related to thunderstorms.
和田 有希*; 榎戸 輝揚*; 久保 守*; 中澤 知洋*; 篠田 太郎*; 米徳 大輔*; 澤野 達哉*; 湯浅 孝行*; 牛尾 知雄*; 佐藤 陽祐*; et al.
Geophysical Research Letters, 48(7), 11 Pages, 2021/04
被引用回数：20 パーセンタイル：90.11(Geosciences, Multidisciplinary)graupels
和田 有希*; 榎戸 輝揚*; 中澤 知洋*; 小高 裕和*; 古田 禄大; 土屋 晴文
Journal of Geophysical Research; Atmospheres, 125(20), p.e2020JD033193_1 - e2020JD033193_17, 2020/10
被引用回数：3 パーセンタイル：15.82(Meteorology & Atmospheric Sciences)We report simulation results of photonuclear reactions in the atmosphere triggered by a downward terrestrial gamma-ray flash in lightning. Possible channels of reactions in the atmosphere and their cross sections are verified with the ENDF/B-VII.1 library. Monte-Carlo simulations with two stages are then performed with the Geant4 framework. In the first stage, electrons following the relativistic runaway electron avalanche spectrum are produced in a mass model of the atmosphere, and production of photoneutrons and 
-decay nuclei is calculated based on the nuclear data library. In total 1
neutrons and 4
-decay nuclei are produced by 
energetic electrons above 1 MeV. In the second stage, propagation of the photoneutrons and positrons from the -decay nuclei in the previous stage is calculated. As a result, we model on-ground distributions of fluxes and energy spectra for neutrons, neutron-related gamma rays, and annihilation ones. The simulation model is to be compared with photonuclear events detected in low-charge-center winter thunderstorms.
和田 有希*; 榎戸 輝揚*; 中澤 知洋*; 湯浅 孝行*; 古田 禄大; 小高 裕和*; 牧島 一夫*; 土屋 晴文
Journal of Geophysical Research; Atmospheres, 125(20), p.e2020JD033194_1 - e2020JD033194_15, 2020/10
被引用回数：2 パーセンタイル：9.97(Meteorology & Atmospheric Sciences)During a winter thunderstorm on 6th February 2017 in Japan, photonuclear reactions such as 
N(
)
N were triggered by a downward terrestrial gamma-ray flash (TGF), as reported by Enoto et al. (2017). In the present paper, we compare the observation with a simulation model of downward TGFs and subsequent photonuclear reactions constructed by the first paper of the series and Wada, Enoto, Nakazawa, et al. (2019). The observation and model consist of three components: annihilation gamma rays from positrons produced by 
-decay nuclei, de-excitation gamma rays originating from neutron captures, and radiation doses by TGF photons. Each component of the observation is reproduced by the simulation model, and we constrain a relation between the number of avalanche electrons and their production altitude of the downward TGF. The constrains by three components match within an order of magnitude. The downward TGF is estimated to comprise 
10
avalanche electrons above 1 MeV produced at an altitude of 1.4-2.7 km. Despite differences in altitude, direction, and season, downward TGFs in winter thunderstorms are thought to have the same mechanism of electron acceleration and multiplication in lightning as TGFs observed by in-orbit satellites.
湯浅 孝行*; 和田 有希*; 榎戸 輝揚*; 古田 禄大; 土屋 晴文; 久富 章平*; 辻 結菜*; 奥田 和史*; 松元 崇弘*; 中澤 知洋*; et al.
Progress of Theoretical and Experimental Physics (Internet), 2020(10), p.103H01_1 - 103H01_27, 2020/10
被引用回数：15 パーセンタイル：74.18(Physics, Multidisciplinary)We designed, developed, and deployed a distributed sensor network aiming at observing high-energy ionizing radiation, primarily gamma rays, from winter thunderclouds and lightning in coastal areas of Japan. Starting in 2015, we have installed, in total, more than 15 units of ground-based detector system in Ishikawa Prefecture and Niigata Prefecture, and accumulated 551 days of observation time in four winter seasons from late 2015 to early 2019. In this period, our system recorded 51 gamma-ray radiation events from thundercloud and lightning. Highlights of science results obtained from this unprecedented amount of data include the discovery of photonuclear reaction in lightning which produces neutrons and positrons along with gamma rays, and deeper insights into the life cycle of a particle-acceleration and gamma-ray-emitting region in a thunder-cloud. The present paper reviews objective, methodology, and results of our experiment, with a stress on its instrumentation.
和田 有希*; 中澤 知洋*; 榎戸 輝揚*; 古田 禄大; 湯浅 孝行*; 牧島 一夫*; 土屋 晴文
Physical Review D, 101(10), p.102007_1 - 102007_6, 2020/05
被引用回数：1 パーセンタイル：8.09(Astronomy & Astrophysics)During a winter thunderstorm on November 24, 2017, a downward terrestrial gamma-ray flash took place and triggered photonuclear reactions with atmospheric nitrogen and oxygen nuclei, coincident with a lightning discharge at the Kashiwazaki-Kariwa nuclear power station in Japan. We directly detected neutrons produced by the photonuclear reactions with gadolinium orthosilicate scintillation crystals installed at sea level. Two gadolinium isotopes included in the scintillation crystals, 
Gd and 
Gd, have large cross sections of neutron captures to thermal neutrons such as Gd(n,
)
Gd and Gd(n,)
Gd. De-excitation gamma rays from Gd and Gd are self-absorbed in the scintillation crystals, and make spectral-line features which can be distinguished from other non-neutron signals. The neutron burst lasted for 100 ms, and neutron fluences are estimated to be 
58 and 31 neutrons cm at two observation points at the power plant. Gadolinium orthosilicate scintillators work as valid detectors for thermal neutrons in lightning.
和田 有希*; 榎戸 輝揚*; 中村 佳敬*; 森本 健志*; 佐藤 光輝*; 牛尾 知雄*; 中澤 知洋*; 湯浅 孝行*; 米徳 大輔*; 澤野 達也*; et al.
Journal of Geophysical Research; Atmospheres, 125(4), p.e2019JD031730_1 - e2019JD031730_11, 2020/02
被引用回数：21 パーセンタイル：80.58(Meteorology & Atmospheric Sciences)During 2017-2018 winter operation of the Gamma-Ray Observation of Winter Thunderclouds experiment in Japan, two downward terrestrial gamma-ray flashes (TGFs) that triggered atmospheric photonuclear reactions were detected. They took place during winter thunderstorms on 5 December 2017 and 9 January 2018 at Kanazawa, Ishikawa Prefecture, Japan. Each event coincided with an intracloud/intercloud discharge, which had a negative-polarity peak current higher than 150 kA. Their radio waveforms in the low-frequency band are categorized as a distinct lightning type called energetic in-cloud pulse (EIP). Negative-polarity EIPs have been previously suggested to be highly associated with downward TGFs, and the present observations provide evidence of the correlation between them for the first time. Furthermore, both of the downward TGFs followed gamma-ray glows, minute-lasting high-energy emissions from thunderclouds. It is suggested that the negative EIPs took place with downward propagating negative leaders or upward positive ones developed in highly electrified regions responsible for the gamma-ray glows.
和田 有希*; 榎戸 輝揚*; 中澤 知洋*; 古田 禄大; 湯浅 孝行*; 中村 佳敬*; 森本 健志*; 松元 崇弘*; 牧島 一夫*; 土屋 晴文
Physical Review Letters, 123(6), p.061103_1 - 061103_6, 2019/08
被引用回数：33 パーセンタイル：88.25(Physics, Multidisciplinary)During a winter thunderstorm on 2017 November 24, a strong burst of gamma-rays with energies up to 10 MeV was detected coincident with a lightning discharge, by scintillation detectors installed at Kashiwazaki-Kariwa Nuclear Power Plant at sea level in Japan. The burst had a sub-second duration, which is suggestive of photoneutron productions. The leading part of the burst was resolved into four intense gamma-ray bunches, each coincident with a low-frequency radio pulse. These bunches were separated by 0.7
1.5 ms, with a duration of 
1 ms each. Thus, the present burst may be considered as a "downward" terrestrial gamma-ray flash (TGF), which is analogous to up-going TGFs observed from space. Although the scintillation detectors were heavily saturated by these bunches, the total dose associated with them was successfully measured by ionization chambers, employed by nine monitoring posts surrounding the power plant. From this information and Monte Carlo simulations, the present downward TGF is suggested to have taken place at an altitude of 2500500 m, involving 
avalanche electrons with energies above 1 MeV which is comparable to those in up-going TGFs.
和田 有希*; 榎戸 輝揚*; 中村 佳敬*; 古田 禄大; 湯浅 孝行*; 中澤 知洋*; 森本 健志*; 佐藤 光輝*; 松元 崇弘*; 米徳 大輔*; et al.
Communications Physics (Internet), 2(1), p.67_1 - 67_9, 2019/06
被引用回数：49 パーセンタイル：93.08(Physics, Multidisciplinary)Two types of high-energy events have been detected from thunderstorms. One is "terrestrial gamma-ray flashes" (TGFs), sub-millisecond emissions coinciding with lightning discharges. The other is minute-lasting "gamma-ray glows". Although both phenomena are thought to originate from relativistic runaway electron avalanches in strong electric fields, the connection between them is not well understood. Here we report unequivocal simultaneous detection of a gamma-ray glow termination and a downward TGF, observed from the ground. During a winter thunderstorm in Japan on 9 January 2018, our detectors caught a gamma-ray glow, which moved for 
100 s with ambient wind, and then abruptly ceased with a lightning discharge. Simultaneously, the detectors observed photonuclear reactions triggered by a downward TGF, whose radio pulse was located within 1 km from where the glow ceased. It is suggested that the highly-electrified region producing the glow was related to the initiation of the downward TGF.
和田 有希*; Bowers, G. S.*; 榎戸 輝揚*; 鴨川 仁*; 中村 佳敬*; 森本 健志*; Smith, D.*; 古田 禄大*; 中澤 知洋*; 湯浅 孝行*; et al.
Geophysical Research Letters, 45(11), p.5700 - 5707, 2018/06
被引用回数：31 パーセンタイル：81.84(Geosciences, Multidisciplinary)An on-ground observation program for high energy atmospheric phenomena in winter thunderstorms along Japan Sea has been performed via lightning measurements of -ray radiation, atmospheric electric field and low-frequency radio band. On February 11, 2017, the radiation detectors recorded -ray emission lasting for 75 sec. The -ray spectrum extended up to 20 MeV and was reproduced by a cutoff power-law model with a photon index of 1.36
, being consistent with a Bremsstrahlung radiation from a thundercloud (as known as a -ray glow). Then the -ray glow was abruptly terminated with a nearby lightning discharge. The low-frequency radio monitors, installed 50 km away from Noto School, recorded intra/inter-cloud discharges spreading over 60km area with a 300 ms duration. The timing of the -ray termination coincided with the moment when a sequence of intra/inter-cloud discharges passed 0.7 km horizontally away from the radiation monitors. The atmospheric electric-field measurement presented that negative charge was located in the cloud base and not neutralized by the lightning discharge. This indicates that the -ray source was located at an higher region than the cloud base.
榎戸 輝揚*; 和田 有希*; 古田 禄大*; 中澤 知洋*; 湯浅 孝行*; 奥田 和史*; 牧島 一夫*; 佐藤 光輝*; 佐藤 陽祐*; 中野 俊男*; et al.
Nature, 551(7681), p.481 - 484, 2017/11
被引用回数：116 パーセンタイル：97.64(Multidisciplinary Sciences)Relativistic electrons accelerated by electric fields of lightnings and thunderclouds emit bremsstrahlung rays, which have been detected at ground observations. The energy of the rays is sufficiently high to potentially invoke atmospheric photonuclear reactions N(, n)N, which would produce neutrons and eventually positrons via decay of generated unstable radioactive isotopes, especially N. However, no clear observational evidence for the reaction has been reported to date. Here we report the first detection of neutron and positron signals from lightning with a ground observation. During a thunderstorm on 6 February 2017 in Japan, an intense -ray flash (1 ms) was detected at our monitoring sites. The subsequent initial burst quickly subsided with an exponential decay constant of 40-60 ms, followed by a prolonged line emission at 0.511MeV, lasting for a minute. The observed decay timescale and spectral cutoff at 10 MeV of the initial emission are well explained with de-excitation rays from the nuclei excited by neutron capture. The centre energy of the prolonged line emission corresponds to the electron-positron annihilation, and hence is the conclusive indication of positrons produced after the lightning. Our detection of neutrons and positrons is unequivocal evidence that natural lightning triggers photonuclear reactions.
小高 裕和*; 一戸 悠人*; 武田 伸一郎*; 福山 太郎*; 萩野 浩一*; 齋藤 新也*; 佐藤 有*; 佐藤 悟朗*; 渡辺 伸*; 国分 紀秀*; et al.
Nuclear Instruments and Methods in Physics Research A, 695, p.179 - 183, 2012/12
被引用回数：23 パーセンタイル：84.01(Instruments & Instrumentation)Si/CdTe半導体両面ストリップ検出器(DSD)を用いた新しいコンプトンカメラの開発を行った。このカメラは、各面において電極が128ストリップ(250
mピッチ)で分割されている、厚さ500mのSi-DSDと4層の厚さ750mのCdTe-DSDから成り、ファインピッチのDSDを4mm間隔で積層配置することで、高角度分解能(356keVで4.5度、662keVで3.5度)を有しかつ小型な装置を実現している。許容できる検出効率を保ちつつこのような高解像度を得るために、コンプトン散乱連続スペクトルを用いたエネルギー較正法と、CdTe-DSD内の深度計測を用いたデータ処理法を新たに試みた。さらに、同時マルチエネルギーイメージングの結果を用いて、カメラの撮像能力について詳細な検討を行った。
-ray camera武田 伸一郎*; 一戸 悠人*; 萩野 浩一*; 小高 裕和*; 湯浅 孝行*; 石川 真之介*; 福山 太郎*; 齋藤 新也*; 佐藤 有*; 佐藤 悟朗*; et al.
Physics Procedia, 37, p.859 - 866, 2012/10
被引用回数：22 パーセンタイル：98.43(Physics, Applied)ASTRO-Hミッションのために開発されたSi/CdTe半導体両面ストリップ検出器(DSD)を利用したコンプトンカメラを用い、放射線ホットスポットのモニタリングの実行可能性チェックを目的とした複数放射線源の画像化実験を行った。本装置は半導体検出器によって与えられた良好なエネルギー分解能により、既に商業的な画像処理システムが提供するホットスポットの画像可能力に加え、複数の放射性同位元素を同定する能力を有する。今回の実験では、
Ba(356keV), 
Na(511keV)及び
Cs(662keV)の三放射性同位元素を同時に測定し、これらの画像化に成功した。5つの検出器モジュール(有効面積: 1.710
cm
)を積み重ねることによって、662keVの線に対し、検出効率1.6810
、及び、3.8度の角度分解能を確認した。本装置は、より多くの検出器モジュールをスタックすることにより、さらに大きな検出効率を達成することが可能である。
高松 邦吉; 沢 和弘; 國富 一彦; 日野 竜太郎; 小川 益郎; 小森 芳廣; 中澤 利雄*; 伊与久 達夫; 藤本 望; 西原 哲夫; et al.
日本原子力学会和文論文誌, 10(4), p.290 - 300, 2011/12
高温工学試験研究炉(HTTR)において平成22年1月から3月にかけて50日間の高温(950
C)連続運転を実施し、水素製造に必要な高温の熱を長期にわたり安定供給できることを世界で初めて示した。本運転の成功により、高温ガス炉の技術基盤を確立するとともに、低炭素社会に向けて温室効果ガスを排出しない革新的な熱化学水素製造等の熱源として原子力エネルギーを利用できることを世界で初めて実証した。
-ray imaging capability with a Si/CdTe semiconductor Compton camera武田 伸一郎*; 青野 博之*; 奥山 翔*; 石川 真之介*; 小高 裕和*; 渡辺 伸*; 国分 紀秀*; 高橋 忠幸*; 中澤 知洋*; 田島 宏康*; et al.
IEEE Transactions on Nuclear Science, 56(3), p.783 - 790, 2009/06
被引用回数：56 パーセンタイル：96.13(Engineering, Electrical & Electronic)A semiconductor Compton camera that combines silicon (Si) and Cadmium Telluride (CdTe) detectors was developed, and its imaging capability was examined with various kinds of -ray targets such as a point source, arranged point sources and an extended source. The camera consists of one double-sided Si strip detector and four layers of CdTe pad detectors, and was designed to minimize the distance between a scatterer and the target. This is because the spatial resolution with Compton imaging improves as the target approaches the scatterer. This new camera realizes a minimum distance of 25 mm. By placing the target at a distance of 30 mm from the detector, resolving power better than 3 mm was demonstrated experimentally for a 364 keV (
I) -ray. Positional determination with accuracy of 1 mm was also demonstrated. As a deconvolution method, we selected the iteration algorithm (called List-Mode Expectation-Maximizing Maximum Likelihood), and applied it to several kinds of experimental data. The Compton back projection images of the arranged point sources and an extended object were successfully deconvolved.
土屋 晴文*; 榎戸 輝揚*; 鳥居 建男; 中澤 知洋*; 湯浅 孝行*; 鳥井 俊輔*; 福山 太郎*; 山口 貴弘*; 加藤 博*; 岡野 眞治*; et al.
Physical Review Letters, 102(25), p.255003_1 - 255003_4, 2009/06
被引用回数：71 パーセンタイル：90.38(Physics, Multidisciplinary)2008年9月20日に標高2770mの乗鞍観測所において線と電子が同時に検出された。これらの放出は、雷雲活動によるもの考えられ90秒続いた。線のエネルギーは10MeVに達し、距離60130mにある線源からの制動放射線によるものと推定された。電子は、雷雲中での加速によって生成されたものと考えられる。
