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Kono, Takahiko; Shimo, Michikuni*; Hayakawa, Hironobu*; Taniguchi, Kazufumi*; Tanaka, Masato*; Tanaka, Hitomi*; Onoue, Yosuke*; Nagaya, Hiroshi*; Torii, Hiroyuki*; Uno, Kazuko*
Hoken Butsuri (Internet), 55(4), p.226 - 238, 2020/12
After the accident at the Fukushima Daiichi Nuclear Power Station, artificial radionuclides such as radioactive cesium and iodine were released into the environment. It caused great anxiety not only in the vicinity of the Fukushima Daiichi Nuclear Power Station but also in other regions of Japan. Some members of the Japan Health Physics Society (JHPS) which is a leading academic society in Japan in the field of radiation protection volunteered to establish the website called "Question and Answer about radiation in Daily Life" just after the accident to reduce the anxiety of the residents about the health effects of radiation. After that, Committee of "Question and Answer about radiation in Daily Life" was established in August 2011 in JHPS, and this activity had been carried out under the responsibility of the society that answered with sincerity against questions from the public as specialists until February 2013. The number of questions on the website had gradually decreased as time passed; therefore, the Committee members decided to end these activities in February 2013. In this paper, following contents were shown; the activities of the Q&A website for about two years, the issues of the stance on our activities, the information related to the website activities and the analysis of Twitter data. Based on the experience and the knowledge obtained from these activities, the issues and experiences that can be utilized in the initial response to emergencies for radiation protection experts as well as other fields are presented.
Onoue, Tetsuji*; Sato, Honami*; Nakamura, Tomoki*; Noguchi, Takaaki*; Hidaka, Yoshihiro*; Shirai, Naoki*; Ebihara, Mitsuru*; Osawa, Takahito; Hatsukawa, Yuichi; Toh, Yosuke; et al.
Proceedings of the National Academy of Sciences of the United States of America, 109(47), p.19134 - 19139, 2012/11
Times Cited Count：40 Percentile：72.81(Multidisciplinary Sciences)The 34 million year (My) interval of the Late Triassic is marked by the formation of several large impact structures on Earth. As with the Chicxulub impact event at the Cretaceous/Paleogene boudary, the Late Triassic impact events have been considered a factor in biotic extinction events in the Late Triassic (e.g., the Triassic/Jurassic boundary). However, the causal link between these impact events and a mass extinction event in the Late Triassic remains controversial because of a lack of stratigraphic records of their ejecta deposits. Here we report evidence for an impact event (platinum group elements anomaly, nickel-rich magnetite and microspherules) deposited within a Paleo-Pacific basin in the middle Norian (Upper Triassic) deep-sea sediment in Japan. This includes anomalously high abundances of iridium, up to 41.5 parts per billion (ppb), in the ejecta deposit, which suggests that the iridium anomaly may be found on a global scale. The middle Norian age of the ejecta deposit suggests that the impact event that produced the 100-km-wide Manicouagan crater in Canada8 is most likely related to its deposition. Our analysis of siliceous microfossils shows no evidence of a mass extinction event across the impact event horizon, and no contemporaneous faunal turnover is seen in other marine fossils. However, such an event has been reported among terrestrial tetrapods and floras in North America. We therefore hypothesize that the Manicouagan impact caused the catastrophic collapse of terrestrial ecosystems near the impact site, but not within the marine realm.
Onoue, Tetsuji*; Sato, Honami*; Nakamura, Tomoki*; Hatsukawa, Yuichi; Osawa, Takahito; Toh, Yosuke; Koizumi, Mitsuo
no journal, ,
We report that an Upper Triassic deep-sea deposit (bedded chert) in Japan, deposited within the Paleo-Pacific (Panthalassa) pelagic basin, contains microspherules, Ni-rich spinels, and iridium anomaly that are characteristic of distal impact ejecta. These indicators of extraterrestrial impact were discovered from a claystone layer in an Upper Triassic bedded chert succession of the Sakahogi section, Inuyama area, central Japan. The age of the impact-related claystone is constrained by the presence of radiolarians and conodonts. We recognized 18 radiolarian species across the claystone. The claystone layer lies between pelagic chert layers of the radiolarian zones Capnodoce-Trialatus and Trialatus robustus-Lysemelas olbia. The last occurrence of Trialatusrobustus, which indicates the Lacian (Early Norian), is a good indicator of the ejecta deposit. Capnodoce serisa and Xiphosphaerafistulata and the co-occurrence of these taxa clearly indicate the late Lacian to early Alaunian (Middle Norian) age for the examined part of the Sakahogi section. Small numbers of conodonts from the claystone include Mockina medionorica, indicating an early Alaunian age (Mockina medionorica Zone). Therefore, the Lacian-Alaunian boundary in the Sakahogi section can belocated around the Capnodoce-Trialatus and Trialatus robustus-Lysemelas olbia Zone boundary.
Sato, Honami*; Onoue, Tetsuji*; Nakamura, Tomoki*; Noguchi, Takaaki*; Hatsukawa, Yuichi; Osawa, Takahito; Toh, Yosuke; Koizumi, Mitsuo
no journal, ,
Microspherules were discovered from a claystone layer (5 cm thick) in an Upper Triassic bedded chert succession of the Sakahogi section, Mino Terrane, Japan. An analysis of radiolarian fossils reveals that the claystone layer is correlated with the early to middle Norian stage of the Upper Triassic. The base of the layer contains 10-15% (by rock volume) green microspherules. Microspherules range in size from 200 to 300 microns. Synchrotron X-ray diffraction analysis indicates that the microspherules are composed mainly of clinoclore. Some microspherules contain a high proportion of small, euhedral to subhedral crystals of oxidized Ni-rich spinels. They are distinguished from typical igneous spinels by high contents of NiO and Fe
. The geochemical signals of extraterrestrial impact are recorded in the claystone layer. Examination of the clay layer using a multiple 
-ray analysis system after neutron activation reveals that microspherules and Ni-rich spinels occur associated with an iridium anomaly, which levels comparable with those at the Cretaceous-Paleogene boudary. A scanning X-ray analytical microscope analysis shows high concentrations of siderophile elements such as nickel and cobalt, which would be expected from an extraterrestrial source.
