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Yamamoto, Yoichi; Kijima, Yuichi; Tomita, Yutaka
no journal, ,
Radionuclide monitoring is the only way to judge whether the target explosion event was a nuclear test. Among the radionuclides produced by the nuclear explosion, the noble gases are particularly important because they are inert and more likely to leak to the ground rather than other substances in an underground nuclear test. Only 4 radioxenon isotopes as the noble gases are monitored for the CTBT verification. It was after the first nuclear test of North Korea in October 2006, when a radioxenon monitoring system installed at the Takasaki radionuclide monitoring station in Japan and the radioxenon monitoring has been carried out since January 2007. We report on the past observation results of the radioxenon at the Takasaki radionuclide monitoring station and the characteristics of radioxenon background.
Yamamoto, Yoichi; Kijima, Yuichi; Tomita, Yutaka
no journal, ,
After the Great East Japan Earthquake in 2011, the Fukushima Daiichi Nuclear Power Plant accident happened and large amounts of radioactive materials were released into the environment and spread globally. The National Data Center-2 (NDC-2) in the Japan Atomic Energy Agency received observation data every day sent from the radionuclide monitoring network of the CTBT International Monitoring System and analyzed the data. The radionuclides released by the accident generally circulated around the northern hemisphere in about 12 days. The activity concentration of Xenon-133 around each radionuclide station in the northern hemisphere almost became uniformed by diffusion in early April, 2011, and after that, the activity concentration at each station decreased with the half-life of Xe-133 and returned to the normal level before the accident in early June. NDC-2 also estimated the timing of first arrival of the radioactive plume at the CTBT Takasaki radionuclide station using the observation data of the station. Consistent results were found between the estimated timing and the time when the spatial gamma-ray dose rate at the monitoring post neat the station rose suddenly.
Purtschert, R.*; Kalinowski, M.*; Riedmann, R.*; Fontaine-Lagrand, J.-E.*; Kusmierczyk-Michulec, J.*; Gheddou, A.*; Bourgouin, P.*; Tomita, Yutaka
no journal, ,
Argon-37 (
Ar) is produced in the high troposphere by spallation of argon through 
Ar(n,4n)Ar and by neutron capture, 
Ar(n,
)Ar. The resulting natural equilibrium concentration of Ar in the mixed troposphere is about 0.5-1 mBq/m
. This value may define the background level for the use of Ar for search area reduction by means of atmospheric Ar measurements in downwind direction of a potential test area in the course of an OSI. In order to investigate long term atmospheric activity levels of Ar, bulk air samples were collected close to the CTBTO IMS Radionuclide station located in Takasaki, Japan. In the years 2016-2018 in total 105 air samples were taken and analyzed for their Ar activity concentrations with no value exceeding 10 mBq/m.