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Okuno, Mitsuru*; Nagaoka, Shinji*; Kokubu, Yoko; Nakamura, Toshio*; Kobayashi, Tetsuo*
Fukuoka Daigaku Rigaku Shuho, 48(1), p.1 - 5, 2018/03
Kuju volcanic group, located in central Kyushu, Japan, consists of over twenty volcanoes (lava domes as well as small stratovolcanoes). The Kurodake is largest lava dome with a volume of 1.6 km
, and generated Kurodake pyroclastic-flow (Kj-Kd) and ash-fall (Kj-KdA) deposits. To refine age of the Kurodake eruption, we conducted radiocarbon dating of a charcoal fragment in the Kj-Kd with an AMS system at Tono Geoscience Center, JAEA. The obtained 
C date, 1505
40 BP, can correspond to 1310-1423 cal BP (probability= 74.6%), 1430-1442 cal BP (2.4%) and 1456-1521 cal BP (23.0%) in 2
confidence level. The medium probability date, 1391 cal BP, is consistent with the stratigraphy and gives the reliable age for the Kj-Kd.
Okuno, Mitsuru*; Nagaoka, Shinji*; Kokubu, Yoko; Nakamura, Toshio*; Kobayashi, Tetsuo*
Radiocarbon, 59(2), p.483 - 488, 2017/00
Times Cited Count：3 Percentile：14.08(Geochemistry & Geophysics)We present here results of AMS C dating to refine the history of the middle and western parts of the Kuju Volcanic Group, located in middle Kyushu, Japan, which consists of more than 20 lava domes and cones. C dating has conducted by AMS (JAEA-AMS-TONO) under the Common-Use Facility Program of JAEA. The Handa PF deposits, which are products of the largest eruption of the group, were dated to 
53.5 ka BP. The Shirani and Muro PF deposits, which are block-and-ash flows, were dated to 44 to 
50 cal ka BP and 3539 cal ka BP, respectively. These ages can be correlated with the TL ages for the lava domes. Therefore, both TL and C methods can be useful tools in establishing the eruptive sequence of lava domes and pyroclastic flows. This study also demonstrates that these eruptive activities occurred after the Handa pfl, the biggest eruption during the last 150 kyrs without a significant time interval.
Okuno, Mitsuru*; Nagaoka, Shinji*; Kokubu, Yoko
Gekkan Chikyu, 37(4), p.119 - 121, 2015/04
Onidake scoria fall deposit at Goto-Fukue Island, Japan is a product of the latest eruption of the Onidake volcano group. Radiocarbon date and C/N ratio of humic soil below the deposit are 19,840120 BP and 9.14, respectively. It shows that the soil proceeded with decomposition in part and the date might be younger than the true one. However the date is older than the result (18,090100 BP) in the soil of the same layer reported by Nagaoka and Furuyama (2004) and is consistent with stratigraphical correlation with widespread tephra such as AT and K-Ah. The calibrated date is approximately 24 cal kBP.
Cs released from Nagasaki atomic bomb in sediment of Nishiyama reservoir at NagasakiKokubu, Yoko; Yasuda, Kenichiro; Magara, Masaaki; Miyamoto, Yutaka; Sakurai, Satoshi; Usuda, Shigekazu; Yamazaki, Hideo*; Yoshikawa, Shusaku*; Nagaoka, Shinji*; Mitamura, Muneki*; et al.
Journal of Environmental Radioactivity, 99(1), p.211 - 217, 2008/01
Times Cited Count：19 Percentile：40.5(Environmental Sciences)In a sediment core of Nishiyama reservoir at Nagasaki, depth profiles of 
Pu/
Pu ratio, 
Pu and Cs concentrations were determined. Sediments containing plutonium and Cs, which were fallout deposited immediately after a detonation of Nagasaki atomic bomb, were identified in the core. Observed below the sediments were macroscopic charcoals, providing evidence for initial deposit of the fallout. This is the first entire depositional records of plutonium and Cs released from the Nagasaki atomic bomb together with those from atmospheric nuclear tests.
Kokubu, Yoko; Yasuda, Kenichiro; Magara, Masaaki; Miyamoto, Yutaka; Sakurai, Satoshi; Usuda, Shigekazu; Murakami, Akiko*; Inoue, Jun*; Yoshikawa, Shusaku*; Yamazaki, Hideo*; et al.
no journal, ,
no abstracts in English
Kokubu, Yoko; Yasuda, Kenichiro; Magara, Masaaki; Miyamoto, Yutaka; Sakurai, Satoshi; Usuda, Shigekazu; Yoshikawa, Shusaku*; Yamazaki, Hideo*; Nagaoka, Shinji*
no journal, ,
no abstracts in English
Kokubu, Yoko; Yasuda, Kenichiro; Magara, Masaaki; Miyamoto, Yutaka; Sakurai, Satoshi; Usuda, Shigekazu; Yoshikawa, Shusaku*; Yamazaki, Hideo*; Nagaoka, Shinji*
no journal, ,
no abstracts in English
Cs derived from Nagasaki atomic bomb; The Sedimentation in Nishiyama reservoir for the last 60 years and the distribution in surface soil at presentKokubu, Yoko; Yasuda, Kenichiro; Magara, Masaaki; Miyamoto, Yutaka; Sakurai, Satoshi; Usuda, Shigekazu; Yamazaki, Hideo*; Yoshikawa, Shusaku*; Nagaoka, Shinji*
no journal, ,
In order to determine sedimentation of plutonium and Cs derived from Nagasaki atomic bomb for the last 60 years, we measured Pu/Pu ratio and Pu and Cs concentration in a sediment core collected at Nishiyama reservoir in Nagasaki city. A layer where plutonium and Cs deposited immediately after the detonation was specified in the core. Even at present, the plutonium and Cs from the atomic bomb are continuously being deposited together with those of the atmospheric nuclear tests. We also measured the ratios in soils collected at eastern part of Nagasaki prefecture and Kumamoto prefecture and so on to determine the detailed distributions of the plutonium. The ratios in soils collected in the Shimabara peninsula, Kumamoto city and Aso city were relatively lower than value of global fallout from atmospheric nuclear tests. It indicates that the atomic bomb plutonium was deposited between 2 km and about 100 km east from the hypocenter.
Yamazaki, Hideo*; Bessho, Keisuke*; Nishida, Hironori*; Yoshikawa, Shusaku*; Murakami, Akiko*; Tsujimoto, Akira*; Fujiki, Toshiyuki*; Kokubu, Yoko; Magara, Masaaki; Nagaoka, Shinji*
no journal, ,
no abstracts in English
Kokubu, Yoko; Magara, Masaaki; Usuda, Shigekazu; Shinohara, Nobuo; Yamazaki, Hideo*; Yoshikawa, Shusaku*; Murakami, Akiko*; Tsujimoto, Akira*; Nagaoka, Shinji*
no journal, ,
Depth profiles of concentration of Pu and Pu/Pu ratio in the cores collected from the center of the Nagasaki Bay were determined to find depositional records of plutonium released from Nagasaki atomic bomb and other nuclear tests. The ratio in sediment at the depth of about 50 cm was higher than that of the global stratospheric fallout, which might show that the plutonium has come from the nuclear tests carried out around the Marshall Islands. Deposition of plutonium from the Nagasaki atomic bomb will be also reported in the presentation.
Yamazaki, Hideo*; Kawashima, Asami*; Kokubu, Yoko; Nagaoka, Shinji*; Tsujimoto, Akira*; Murakami, Akiko*; Yoshikawa, Shusaku*
no journal, ,
no abstracts in English
Kokubu, Yoko; Magara, Masaaki; Sakurai, Satoshi; Usuda, Shigekazu*; Kimura, Takaumi; Yamazaki, Hideo*; Yoshikawa, Shusaku*; Nagaoka, Shinji*
no journal, ,
Plutonium isotopes were released from Nagasaki atomic bomb which exploded on August 9, 1945. The isotopes are interesting in research on environmental radioactivity, because evident information of the plutonium release provide opportunities to simplify understanding of environmental behavior of Pu. The Nagasaki area is one of the oldest areas that were contaminated with the artificial Pu in the world. As the isotopic composition of Pu depends on its origin, Pu/Pu ratio is a useful tool for the identification of the source of Pu. This paper is intended to report the Pu/Pu ratios in sediments and surface soils and distribution of the Pu from the atomic bomb.
Okuno, Mitsuru*; Nagaoka, Shinji*; Kokubu, Yoko; Nakamura, Toshio*; Kobayashi, Tetsuo*
no journal, ,
Kuju volcano, located between Aso and Yufu-Tsurumi volcanoes in middle Kyushu, Japan, consists of more than 20 eruptive centers. We present here results of AMS radiocarbon dating to refine the history of the middle and western parts of Kuju volcano taking in the ages of Thermoluminescence (TL) dating. Radiocarbon ages for pyroclastic flows of Handa, Shirani and Muro on the southern sector of the volcano were ca. 30 - 50 kBP. These dates can be correlated with the TL ages for the lava domes. These results shows the lava domes formed relatively constant and the pyroclastic flows ran down toward the base of the volcano after the pyroclastic flow of Handa. Eruptions released at different periods are difficult to distinguish each other because their petrographical features are similar. Therefore, both TL and radiocarbon dating methods can be useful tools in establishing the eruptive sequence of lava domes and pyroclastic flows.
Okuno, Mitsuru*; Nagaoka, Shinji*; Kokubu, Yoko; Nakamura, Toshio*; Kobayashi, Tetsuo*
no journal, ,
Kuju Volcanic Group, located in middle Kyushu, Japan, consists of lava domes and small stratovolcanoes. We present here results of AMS C dating of pyroclastic flow deposits (Pfl) on southern slope of the Kuju Volcanic Group. The C dating has conducted by AMS (JAEA-AMS-TONO) under the Common-Use Facility Program of JAEA. The Handa Pfl was the biggest eruption during the last 200 kyrs and the AMS C age was about 54 kBP. Shirani Pfl and Muro Pfl are block-and ash flow type and the C ages were 48 kBP and 41 kBP, 32 - 34 kBP, respectively. These ages can be correlated with Thermoluminescence ages for lava domes of Kutsukake-yama and Hossho-zan. This study demonstrates that the lava dome and block-and ash flow deposits formed at the summit area after the eruption of Handa Pfl.
