Factors regulating the concentration of particulate iodine in coastal seawater

Sato, Yuhi*; Otosaka, Shigeyoshi*; Suzuki, Takashi; Nakanishi, Takahiro

Limnology and Oceanography, 68(7), p.1580 - 1594, 2023/07

https://doi.org/10.1002/lno.12369

To investigate the factors regulating the concentration of particulate iodine (PI) in seawater, it was measured in two Pacific coastal areas adjacent to Japan in two seasons along with parameters such as particulate organic carbon (POC) and nitrogen (PON), dissolved iodine (DI), and phytoplankton pigments. The dataset was divided in three groups namely, lower (Group A), average (Group B), and higher (Group C) atomic ratios of PI to POC (I/C). The three groups were characterized by phytoplanktonic physiological states as highly productive, steady, and senescent states, respectively. Based on the finding that PI production is associated with the phytoplankton physiological state, the seasonal and regional differences in PI concentration and I/C in the observation areas were consistently explained. Finally, we suggest that the phytoplanktonic physiological state is one of the vital factors regulating the PI concentration in seawater.

Distribution and settling behavior of americium-241 in the tropical East Pacific

Kinoshita, Norikazu*; Nagaoka, Mika; Nakanishi, Takashi*

Science of the Total Environment, 753, p.142087_1 - 142087_10, 2021/01

https://doi.org/10.1016/j.scitotenv.2020.142087

The distribution of the anthropogenic radionuclide americium-241 (Am), a decay product of Pu discharged from atmospheric tests of nuclear weapons, was investigated to resolve its horizontal and vertical migration in the Tropical East Pacific. We analyzed Am concentrations in seawater samples collected in 2003. On comparing the Am concentrations with the previously determined concentrations of Pu in the same samples, the vertical profiles of Am were found to be similar to those of Pu. At some stations, the maximum concentration of Am occurred 100-200 m deeper than that of Pu. The Am/Pu ratios in the North Pacific and South Pacific were comparable to one another, and were typical of the ratio for the Pacific. The Am distribution was influenced by the water mass at depths below 400 m. The Am data support the view there is a current flowing at depths of 400-3000 m from the North Pacific through the equator to the South Pacific. In addition, the Am vertical profile was explained by using a box model that considers the decay of Pu and adsorption and scavenging by suspended particles. The different depths for the maximum concentrations of Am and Pu observed at some stations were well explained by the model and by the distribution of CaCO particles. The residence time of Am in the Pacific was also estimated by using the model.

Study on current US views on bilateral civilian nuclear cooperation agreements

Tazaki, Makiko; Tamai, Hiroshi; Shimizu, Ryo; Kimura, Takashi; Kitade, Yuta; Nakanishi, Hiroaki; Suda, Kazunori

Nihon Kaku Busshitsu Kanri Gakkai Dai-39-Kai Nenji Taikai Rombunshu (Internet), 7 Pages, 2018/11

no abstracts in English

Summary of research result of State Level Concept (SLC)

Kimura, Takashi; Tazaki, Makiko; Kitade, Yuta; Shimizu, Ryo; Tamai, Hiroshi; Nakanishi, Hiroaki; Suda, Kazunori

Nihon Kaku Busshitsu Kanri Gakkai Dai-39-Kai Nenji Taikai Rombunshu (Internet), 5 Pages, 2018/11

This is the summary of research result of State Level Concept (SLC) which has been developed and conducted by the IAEA and a major purpose of the research reported here is to promote the nuclear operator's understandings for the importance of Broder Conclusion drawn continuously by the IAEA under SLC.

Vertical and lateral transport of particulate radiocesium off Fukushima

Otosaka, Shigeyoshi; Nakanishi, Takahiro; Suzuki, Takashi; Sato, Yuhi; Narita, Hisashi*

Environmental Science & Technology, 48(21), p.12595 - 12602, 2014/11

https://doi.org/10.1021/es503736d

From August 2011 to July 2013, a sediment trap was deployed at 100 km east of the Fukushima Daiichi Nuclear Power Plant and sinking particles were collected. Sinking flux of Cs decreased over time with seasonal fluctuation. The Cs fluxes were mainly affected by two principal modes. One was a rapid sinking of radiocesium-bound particles (moderate mode). This mode was dominant especially in the early post-accident stage, and was presumed to establish the distribution of radiocesium in the offshore seabed. Another was the secondary transport of particles attributed to turbulence near the seabed and was observed in winter (turbulence mode). Although the latter process would not drastically change the distribution of sedimentary radiocesium, attention should be paid as this key process redistributing the accident-derived radiocesium may cumulatively affect the long-term distribution.

Basic vacuum test of 500-kV photocathode DC gun components at KEK

Yamamoto, Masahiro*; Uchiyama, Takashi*; Miyajima, Tsukasa*; Honda, Yosuke*; Sato, Kotaro*; Matsuba, Shunya*; Saito, Yoshio*; Kobayashi, Masanori*; Kurisu, Hiriki*; Hajima, Ryoichi; et al.

Proceedings of 7th Annual Meeting of Particle Accelerator Society of Japan (DVD-ROM), p.717 - 720, 2010/08

http://www.pasj.jp/web_publish/pasj7/proceedings/P_4PM/P_EH_4PM/WEPS124.pdf

A 500-kV photocathode DC electron gun which can supply the beam of a low emittance and a high average current has been developed in collaboration with KEK, JAEA, Hiroshima Univ., Nagoya Univ. and Yamaguchi Univ. The vacuum of the gun chamber has to be lower Extreme High Vacuum for maintain cathode-life time. A titanium chamber and new material of ceramic were employed to reduce outgassing rate. The result of outgassing rate of the gun chamber is described in this report.

Design of a 500kV electron gun for ERL light source at KEK

Yamamoto, Masahiro*; Honda, Yosuke*; Miyajima, Tsukasa*; Uchiyama, Takashi*; Kobayashi, Masanori*; Muto, Toshiya*; Matsuba, Shunya*; Sakanaka, Shogo*; Sato, Kotaro*; Saito, Yoshio*; et al.

Proceedings of 6th Annual Meeting of Particle Accelerator Society of Japan (CD-ROM), p.860 - 862, 2009/08

A newly 500 kV electron gun (2nd - 500 kV gun) for an ERL light source is designed at KEK. A new concept and state of-the-art technologies of vacuum system, ceramic insulators, high voltage power supply, photocathode and preparation system will be employed. The details are described in this report.

Fe translocation in barley as monitored by a Positron-Emitting Tracer Imaging System (PETIS); Evidence for the direct translocation of Fe from roots to young leaves via phloem

Tsukamoto, Takashi*; Nakanishi, Hiromi*; Uchida, Hiroshi*; Watanabe, Satoshi; Matsuhashi, Shimpei; Mori, Satoshi*; Nishizawa, Naoko*

Plant & Cell Physiology, 50(1), p.48 - 57, 2009/01

https://doi.org/10.1093/pcp/pcn192

New system of nuclear education by network

Hasegawa, Makoto; Nakanishi, Takashi*; Fujii, Yasuhiko*; Odaka, Tomohiro*

Hosha Kagaku Nyusu, (17), p.29 - 35, 2008/03

http://www.radiochem.org/rad-nw/rad_nw17.pdf

no abstracts in English

Mutational reconstructed ferric chelate reductase confers enhanced tolerance in rice to iron deficiency in calcareous soil

Ishimaru, Yasuhiro*; Kim, S.*; Tsukamoto, Takashi*; Oki, Hiroyuki*; Kobayashi, Takanori*; Watanabe, Satoshi; Matsuhashi, Shimpei; Takahashi, Michiko*; Nakanishi, Hiromi*; Mori, Satoshi*; et al.

Proceedings of the National Academy of Sciences of the United States of America, 104(18), p.7373 - 7378, 2007/05

https://doi.org/10.1073/pnas.0610555104