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.

Practical guide on soil sampling, treatment, and carbon isotope analysis for carbon cycle studies

Koarashi, Jun; Atarashi-Andoh, Mariko; Nagano, Hirohiko*; Sugiharto, U.*; Saengkorakot, C.*; Suzuki, Takashi; Kokubu, Yoko; Fujita, Natsuko; Kinoshita, Naoki; Nagai, Haruyasu; et al.

JAEA-Technology 2020-012, 53 Pages, 2020/10

JAEA-Technology-2020-012.pdf:3.71MB

There is growing concern that recent rapid changes in climate and environment could have a significant influence on carbon cycling in terrestrial ecosystems (especially forest ecosystems) and could consequently lead to a positive feedback for global warming. The magnitude and timing of this feedback remain highly uncertain largely due to a lack of quantitative understanding of the dynamics of organic carbon stored in soils and its responses to changes in climate and environment. The tracing of radiocarbon (natural and bomb-derived C) and stable carbon (C) isotopes through terrestrial ecosystems can be a powerful tool for studying soil organic carbon (SOC) dynamics. The primary aim of this guide is to promote the use of isotope-based approaches to improve our understanding of the carbon cycling in soils, particularly in the Asian region. The guide covers practical methods of soil sampling; treatment and fractionation of soil samples; preparation of soil samples for C (and stable nitrogen isotope, N) and C analyses; and C, N, and C measurements by the use of isotope ratio mass spectrometry and accelerator mass spectrometry (AMS). The guide briefly introduces ways to report C data, which are frequently used for soil carbon cycling studies. The guide also reports results of a case study conducted in a Japanese forest ecosystem, as a practical application of the use of isotope-based approaches. This guide is mainly intended for researchers who are interested but are not experienced in this research field. The guide will hopefully encourage readers to participate in soil carbon cycling studies, including field works, laboratory experiments, isotope analyses, and discussions with great interest.

Verification of safety margin of reactor pressure vessel exposed to various thermal transients based on probabilistic approach

Suzuki, Masahide*; Murakami, Kenta*; Suzuki, Takashi*; Okayama, Ryuta*; Katsuyama, Jinya; Li, Y.

E-Journal of Advanced Maintenance (Internet), 11(4), p.172 - 178, 2020/02

https://www.jsm.or.jp/ejam/Vol.11No.4/AA/AA171/AA171.html

no abstracts in English

Distribution and fate of I in the seabed sediment off Fukushima

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

Journal of Environmental Radioactivity, 192, p.208 - 218, 2018/12

AA2017-0744.pdf:1.17MB

https://doi.org/10.1016/j.jenvrad.2018.06.025

From August 2011 to October 2013, the concentration of iodine-129 (I) in the seabed sediment collected from 26 stations located within 160 km from the Fukushima Daiichi Nuclear Power Plant was estimated. The concentrations of I in seabed sediment off Fukushima in 2011 ranged between 0.02 and 0.45 mBq/kg. Although iodine is a biophilic element, the accident-derived radioiodine negligibly affects the benthic ecosystem. Until October 2013, a slightly increased activity of I in the surface sediment in the shelf-edge region (bottom depth: 200-400 m) was observed. The increase of the I concentrations in the shelf-edge sediments was affected by the (1) transport of I-bound particles from the land through rivers and (2) re-deposition of I desorbed from the contaminated coastal sediment to the shelf-edge sediments, which were considered to be dominant processes.

Impacts of anthropogenic source from the nuclear fuel reprocessing plants on global atmospheric iodine-129 cycle; A Model analysis

Kadowaki, Masanao; Katata, Genki*; Terada, Hiroaki; Suzuki, Takashi; Hasegawa, Hidenao*; Akata, Naofumi*; Kakiuchi, Hideki*

Atmospheric Environment, 184, p.278 - 291, 2018/07

AA2017-0580.pdf:2.03MB

https://doi.org/10.1016/j.atmosenv.2018.04.044

The long-lived radioactive iodine (I) is a useful geochemical tracer in the atmospheric environment. We recently observed clear seasonal trends in air concentration and deposition of I in Japan. Using these data, we developed a global atmospheric I transport model to reveal key processes for the global atmospheric I cycle. The model generally reproduced the observed seasonal change in air concentration and deposition of I in Japan, and the global distribution of I concentration in rain as presented in past literature. Numerical experiments changing the intensity of anthropogenic and natural sources were conducted to quantify the impact of anthropogenic sources on the global I cycle. The results indicated that the atmospheric I from the anthropogenic sources was deposited in winter and can be accumulated mainly in the northern part of Eurasia. In contrast, the atmospheric I from the natural sources dominated the deposition in summer. These results suggested that the re-emission process of I from the Earth's surface may be important as a secondary impact of I in the global-scaled environment. Furthermore, although wet deposition dominated the total deposition in the Northern hemisphere, dry deposition regionally and seasonally contributed to the total deposition over arctic and northern part of Eurasia in winter, suggesting that the dry deposition may play a key role in the seasonal change of I deposition in the Northern hemisphere high latitudes.

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.

Chapter 2 "Radiation measurement" and Chapter 3 "Measurement and estimation of exposed dose"

Yoshizawa, Michio; Suzuki, Takashi; Noguchi, Masayasu*

Hoshasen Anzen Kanri No Jissai 3-Han, p.39_90 - 91_120, 2013/10

It was decided to revise the book of "Actual Radiation Safety Management", which has been used as a main text for the radiation protection supervisors, in order to reflect the latest amendment of the Radiation Hazards Prevention Act. Then, we revised Chapter 2 "Radiation measurement" and Chapter 3 "Measurement and estimation of exposed dose" of the book, which were the writing parts of the current version, so as to incorporate the most up-to-date information. Main subjects of these revises were the change of radiation and tissue weighting factors in the 2007 recommendations of the International Commission on Radiological Protection (ICRP), update of the information about survey meters and personal dosimeters, clarification of sentences and so on.

Distribution of iodine-129 in the northwestern North Pacific Ocean between Jan and Feb 2012

Suzuki, Takashi; Otosaka, Shigeyoshi; Kuwabara, Jun

Dai-15-Kai AMS Shimpojiumu Hokokushu, p.49 - 52, 2013/03

no abstracts in English

Strong correlation among structural, electronic, and magnetic properties of SrFeMoO (0 x 1)

Yoshida, Koji*; Ikeuchi, Shinya*; Shimizu, Hajime*; Okayasu, Satoru; Suzuki, Takashi*

Journal of the Physical Society of Japan, 80(4), p.044716_1 - 044716_4, 2011/04

https://doi.org/10.1143/JPSJ.80.044716

We studied systematic changes of the structural, electric, and magnetic properties in SrFeMoO with 0 x 1, which bridges between a half-metallic double perovskite SrFeMoO (x = 0) and an antiferromagnetic metal SrFeO (= SrFeO: x = 1). The lattice volume at room temperature linearly decreases with x. The decline steeply enhances around x = 0.5, which is accompanied with a symmetry change from a tetragonal to a cubic crystal structure. In the same composition, we also found changes in the electronic ground state from a metal to an insulator and in the magnetic one from ferromagnetism to paramagnetism. These results indicate the strong correlation among the crystal structure, itinerant electrons and occurrence of ferromagnetic state in the double perovskite. In addition, the value of the critical composition could reflect peculiar physical changes with x.

Status of JAEA-AMS-MUTSU

Tanaka, Takayuki; Kabuto, Shoji; Kinoshita, Naoki; Suzuki, Takashi; Kuwabara, Jun; Seki, Takeo

Dai-13-Kai AMS Shimpojiumu Hokokusho, p.129 - 132, 2011/01

An accelerator mass spectrometry at Aomori Research and Development Center, JAEA (JAEA-AMS-MUTSU) was established in 1997 and the routine operation of C and I measurement was started from 1999 and 2003, respectively. This AMS has adopted the open door policy for the general users from the fiscal year of 2006 and various researches have been in progress by many users. In this presentation, we introduce the status of JAEA-AMS-MUTSU. The total number of measurements has increased well for five years after the open door policy excluding in 2008. The reasons for the decrease in 2008 were that we had stopped the operation of AMS for about one and half months because the operation system of AMS was upgraded, and that we could not measure the C for several months because the amplifier of detector had broken. We had resolved this trouble and our AMS can measure smoothly both C and I.