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Oral presentation

Lateral distributions of Th-228 activity and Ra-228/Ra-226 activity ratio of surface water within the Sea of Japan, the East China Sea, and the Sea of Okhotsk

Yoshida, Keisuke*; Inoue, Mutsuo*; Minakawa, Masayuki*; Nakano, Yusuke*; Kofuji, Hisaki*; Otosaka, Shigeyoshi; Kiyomoto, Yoko*; Shiomoto, Akihiro*; Hamajima, Yasunori*; Yamamoto, Masayoshi*

no journal, , 

The authors have developed an analytical method for Th-228, Ra-226 and Ra-228 measurements in seawater using an ultra-low background $$gamma$$-ray detector. In this study, the authors measured the three radionuclides in surface seawater obtained from 16 stations in the Japan Sea, East China Sea and Okhotsk Sea. Concentrations of Ra-228 and Th-228 in surface waters in the southern Japan Sea were lower than those in the northern regions. Considering that the Th-228/Ra-228 activity ratios were not different between the northern and southern regions of the Japan Sea, we could conclude that (1) input of terrestrial materials from the East China Sea has not affected the distribution of the radionuclides in the Japan Sea, and (2) the efficiency of scavenging was not different between the regions.

Oral presentation

Transport and supply process of $$^{22}$$Na and $$^{7}$$Be depositions in Tsuruga city

Yoshida, Keisuke; Kato, Shingo; Inoue, Mutsuo*; Ishizuka, Akihiro; Okuyama, Shinichi

no journal, , 

$$^{22}$$Na is observed for environmental monitoring of Monju fast breeder reactor because Monju reactor contains $$^{22}$$Na in primary coolant. But $$^{22}$$Na is produced in upper atmosphere, therefore, $$^{22}$$Na is detected in assembled deposition sample. To increase accuracy of environmental monitoring, it is necessary to understand transport and supply process of $$^{22}$$Na and $$^{7}$$Be depositions from high latitude region where a lot of $$^{22}$$Na is produced. We collect deposition samples at Tsuruga city to measure $$^{22}$$Na and collect $$^{7}$$Be deposition data in 5 sites in Fukui prefecture and Ishikawa prefecture. Because $$^{22}$$Na and $$^{7}$$Be shows good correlation, $$^{22}$$Na have same behavior with $$^{7}$$Be. $$^{7}$$Be deposition is maximum at Kanazawa city and minimum at Shika town, but $$^{7}$$Be deposition is maximum in Winter season at all sites. $$^{7}$$Be deposition and precipitation shows correlation. From the above, Winter monsoon transport $$^{7}$$Be and $$^{22}$$Na from high latitude region and precipitation provide these nuclides to ground surface at Tsuruga city. The deference of $$^{7}$$Be deposition in Winter season is likely owing to height of mountain and distance of sampling sites.

Oral presentation

Variation of Be-7 and Na-22 in deposition sample and mesoscale meteorological phenomena in Tsuruga city in winter season

Kato, Shingo; Yoshida, Keisuke; Inoue, Mutsuo*; Yamashita, Masahiro; Okuyama, Shinichi; Ishimori, Yuu

no journal, , 

no abstracts in English

Oral presentation

Temporal and lateral variations of $$^{7}$$Be depositions in Hokuriku, Japan

Yoshida, Keisuke; Kato, Shingo; Uchida, Kengo*; Yamashita, Masahiro; Okuyama, Shinichi; Inoue, Mutsuo*

no journal, , 

In winter, $$^{7}$$Be deposition profile shows wide variation in Hokuriku region. Temporal and regional variations of $$^{7}$$Be deposition data during 30 years (Apr. 1991 to Mar. 2021) were analyzed and material transport mechanisms from arctic region were studied. Due to pressure pattern around Japan in winter and inhomogeneous precipitation in Hokuriku region caused by topography, characteristic seasonal variation was found and highest $$^{7}$$Be deposition was observed in mountainous area in Kanazawa City. In addition, the period of high $$^{7}$$Be deposition observed approximately agreed with that of minimum sunspot number or maximum precipitation. Therefore, sunspot number and precipitation affect temporal variations of $$^{7}$$Be deposition.

Oral presentation

Fluctuation of $$^{7}$$Be and $$^{22}$$Na deposition in the Hokuriku region in winter

Yoshida, Keisuke; Tsunokawa, Shoji; Umeda, Masayuki; Yamashita, Masahiro; Nakano, Masanao; Ishimori, Yuu; Inoue, Mutsuo*

no journal, , 

no abstracts in English

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