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Journal Articles

Vertical distributions of Iodine-129 and iodide in the Chukchi Sea and Bering Sea

Miwa, Kazuji; Obata, Hajime*; Suzuki, Takashi

Journal of Nuclear Science and Technology, 57(5), p.537 - 545, 2020/05

 Times Cited Count:1 Percentile:23.13(Nuclear Science & Technology)

This study investigated the vertical distribution of Iodine-129 ($$^{129}$$I) which is mainly produced by European nuclear reprocessing plants in the Chukchi Sea and Bering Sea. $$^{129}$$I was found to be distributed almost uniformly in fallout level, and an increasing in $$^{129}$$I concentration levels caused by high $$^{129}$$I water inflow from the Atlantic Ocean was not observed. Additionally, we revealed the vertical distribution of iodide, one chemical form of iodine, from the Bering Shelf area to the Chukchi Sea for the first time. The increasing tendency of iodide near sea bottom was observed.

Journal Articles

Rapid collection of iron hydroxide for determination of Th isotopes in seawater

Okubo, Ayako; Obata, Hajime*; Magara, Masaaki; Kimura, Takaumi; Ogawa, Hiroshi*

Analytica Chimica Acta, 804, p.120 - 125, 2013/12

 Times Cited Count:2 Percentile:8.87(Chemistry, Analytical)

This work introduces a novel method of recovery of iron hydroxide using a DIAION CR-20 chelating resin column to determine Th isotopes in seawater with a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). Thorium isotopes in seawater were coprecipitated with iron hydroxide, and this precipitate was sent to chelating resin column. The chelating column quantitatively collected $$^{232}$$Th with iron hydroxide in seawater at flow rates of 20-25 mL/min. Based on this flow rate, a 5 L sample was processed within 3-4 h.

Journal Articles

Atmospheric deposition of trace metals to the western North Pacific Ocean observed at coastal station in Japan

Okubo, Ayako; Takeda, Shigenobu*; Obata, Hajime*

Atmospheric Research, 129-130, p.20 - 32, 2013/07

 Times Cited Count:34 Percentile:73.29(Meteorology & Atmospheric Sciences)

To understand the atmospheric input of trace metals to surface seawaters, the total deposition samples were collected simultaneously from three coastal station in Japan. The observed flux was within the lower limit of the previous estimation based on a model. Except for Sc and Fe, all the elements showed a increasing tendency toward dissolution with decreasing the pH. We calculated the Sc-normalized enrichment factors. The increasing tendency toward dissolution with decreasing the pH was higher for Al than that of Fe.

Journal Articles

$$^{230}$$Th and $$^{232}$$Th distributions in mid-latitudes of the North Pacific Ocean; Effect of bottom scavenging

Okubo, Ayako; Obata, Hajime*; Gamo, Toshitaka*; Yamada, Masatoshi*

Earth and Planetary Science Letters, 339-340, p.139 - 150, 2012/07

 Times Cited Count:34 Percentile:73.65(Geochemistry & Geophysics)

Vertical distributions of total $$^{230}$$Th and dissolved $$^{232}$$Th were determined in the mid-latitudes of the North Pacific Ocean. Th in the Pacific Ocean have been described well using the reversible-scavenging model. However, we observed the depletion of total Th. The enhanced vertical eddy diffusion derived from the complex topography of the western Pacific Ocean might promote bottom scavenging and transport of the low Th in deep water to the upper layers.

Oral presentation

Vertical distributions of $$^{230}$$Th in the Pacific Ocean and their relation to advection and diffusion

Okubo, Ayako; Obata, Hajime*; Gamo, Toshitaka*; Yamada, Masatoshi*

no journal, , 

We investigated the vertical distribution of total $$^{230}$$Th in mid latitudes of the Pacific Ocean. The west to east section of $$^{230}$$Th shows a strong gradient in the deep waters around 170 degree east and 110 degree west. At depths of 2000 to 4000 m and 4000 m to bottom within the time-scale of scavenging residence time of $$^{230}$$Th, the horizontal eddy diffusion could reach 1100 to 1400 km and 400 to 700 km, respectively. The horizontal eddy diffusion transport is too weak to affect Th distribution in the deep layers between each station in this study area.

Oral presentation

Rapid collection of iron hydroxiedes for determination of Th isotopes in seawater using polyamin type chelating resin

Okubo, Ayako; Obata, Hajime*; Magara, Masaaki; Kimura, Takaumi; Ogawa, Hiroshi*

no journal, , 

This work introduces a novel method of recovery of iron hydroxide with thorium using a DIAION CR-20 chelating resin column to determine Th isotopes in seawater with a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). Thorium isotopes in seawater were co-precipitated with iron hydroxide, and this precipitate was sent to chelating resin column. The chelating column quantitatively collect $$^{232}$$Th with iron hydroxide in seawater at flow rate of 20-25 mL/min. Based on this flow rate, 5 L sample was processed within 3-4 h. The aging of iron hydroxide tends to reduce the recovery of $$^{232}$$Th. The rapid collection method was successfully applied to the determination of$$^{230}$$ Th and $$^{232}$$Th in open-ocean seawater samples.

Oral presentation

Iodine speciation and iodine-129 distribution in the Chukchi Sea and Bering Sea

Obata, Hajime*; Miwa, Kazuji*; Kondo, Yoshiko*; Gamo, Toshitaka*; Otosaka, Shigeyoshi; Suzuki, Takashi

no journal, , 

Distributions chemical species of iodine (iodide, iodate and organic iodine) in seawater were investigated in the Chukchi Sea and Bering Sea, Arctic northern marginal seas. $$^{129}$$I, which is a good tracer for anthropogenically released iodine to the marine environments, were also revealed by this study. Iodide concentrations in seawater often increased toward the seafloor. This tendency was remarkable with iodide and organic iodine, indicating that these iodine species are released from the sediments of the continental shelf. Concentrations of $$^{129}$$I ranged from 0.79 to 2.89$$times$$10$$^{7}$$ atom/L. While this level was several times higher than those in the North Pacific, significant increase of $$^{129}$$I concentration due to seawater inflow from the North Atlantic was not observed. Considering latitudinal range of this study area, it can be estimated that most $$^{129}$$I detected by this study was derived by atmospheric deposition of $$^{129}$$I originates from Europe.

Oral presentation

Distribution and source of I-129 in Chukchi Sea and Bering Sea

Miwa, Kazuji; Obata, Hajime*; Suzuki, Takashi; Otosaka, Shigeyoshi

no journal, , 

I-129 in a global environment is originated from the European nuclear fuel reprocessing plants (NFRP), Sellafield in U.K. and La Hague in France, and it is observed a large amount of I-129 inflows from European NFRP into the eastern and central Arctic Ocean. Previous studies on I-129 at surface indicated seawater with high I-129 concentration does not inflow from eastern and central Arctic Ocean to Chukchi Sea, located in western Arctic Ocean. However, there is a possibility of inflow of I-129 because the vertical distribution of I-129 has not observed at the ocean. The purpose of this study is to identify the inflow of seawater with high I-129 concentration from eastern and central Arctic Ocean by observing the vertical distribution of I-129 and water mass structure in Chukchi Sea and Bering Sea. Seawater with high temperature at surface of southern Chukchi Sea (- 66$$^{circ}$$N) and with low temperature at bottom of the northern Chukchi Sea (69$$^{circ}$$N - ) were observed. The seawater with low temperature might include high I-129 concentration. However, I-129 concentration in some points was observed ranging from 0.79 to 2.89 (10$$^{7}$$atoms/L), which was two orders of magnitude lower than that in the eastern and central Arctic Ocean. And no significant difference of I-129 concentration between seawater at surface and at bottom was shown. Therefore, we could not identify the inflow of seawater with high I-129 concentration from eastern and central Arctic Ocean to Chukchi Sea.

Oral presentation

Study on the generation process of radioactive particles emitted from Unit 1 of FDNPP

Ishii, Tatsuya*; Sueki, Keisuke*; Matsuo, Kazuki*; Kurosawa, Masanori*; Satou, Yukihiko; Kobata, Masaaki; Fukuda, Tatsuo; Yoshii, Kenji; Tanida, Hajime; Okane, Tetsuo; et al.

no journal, , 

Radioactive particles were released into the environment by the accident of Fukushima Daiichi Nuclear Power Plant (FDNPP). They have information to understand the inside of the reactor during the accident. Now, nobody knows the generation process of radioactive particles. In this study, we analyzed (1) elements of particles' cross section with SEM-EDS to reveal what is the material and (2) chemical states of elements on particles' surface with HAXPES. (1) Radioactive particles are composed of the two parts. One is the basic material and the other is the heavy elemental materials. We considered the basic material was soda-lime glass and the heavy elemental materials included lead glass. (2) HAXPES brought out that the chemical states of Cs on particles, surface was different in the Na-poor areas and the Na-rich areas. In the Na-poor areas, the chemical state of Cs showed CsFeSiO$$_4$$ mainly, but zero valence partly. In the Na-rich areas, the chemical state of Cs couldn't be identified. For above analyses, we can reveal the generation process of radioactive particles.

Oral presentation

Hard X-ray photoelectron spectroscopy study of radiation effects of Pt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$

Kobata, Masaaki; Yoshii, Kenji; Fukuda, Tatsuo; Kawasaki, Ikuto; Satou, Yukihiko; Tanida, Hajime; Okane, Tetsuo; Yamagami, Hiroshi; Yaita, Tsuyoshi; Harii, Kazuya; et al.

no journal, , 

We have investigated the electronic structures of Pt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ thin films irradiated by gamma ray and heavy particles. Investigating details of this system is interesting from a possible application of waste heat recovery using the spin Seebeck effect (SSE) due to a tolerance against a presence of atomic defect. Irradiation of $$^{60}$$Co gamma ray does not affect the spectral profiles such as Fe 2$it{p}$, a fact being consistent with the gamma-ray tolerance of SSE as reported previously. On the other hand, the irradiation of Au particles was found to lead to a chemical shift of some photoelectron peaks, suggesting a possible defect of some ions such as Fe$$^{3+}$$.

Oral presentation

Transport and accumulation of particulate $$^{137}$$Cs on the continental shelf off Fukushima

Otosaka, Shigeyoshi*; Misono, Toshiharu; Dohi, Terumi; Tsuruta, Tadahiko; Takahashi, Yoshio*; Sugihara, Naoko*; Obata, Hajime*; Ikenoue, Takahito*; Jimi, Naoto*; Hookabe, Natsumi*

no journal, , 

no abstracts in English

Oral presentation

Status and future of radiocesium in the seafloor off Fukushima

Otosaka, Shigeyoshi*; Aono, Tatsuo*; Fukuda, Miho*; Kambayashi, Shota*; Misono, Toshiharu; Dohi, Terumi; Tsuruta, Tadahiko; Suzuki, Takashi; Takahashi, Yoshio*; Sugihara, Naoko*; et al.

no journal, , 

While the amount of cesium-137 ($$^{137}$$Cs: half-life 30.1 years) accumulated on the seabed due to the accident of the Fukushima Daiichi Nuclear Power Plant (0.1-0.2 PBq) is only about 1 to 2% of the total amount of $$^{137}$$Cs transported to the ocean, it has been reported that it will remain for a long time in the coastal areas. On the other hand, long-term migration process of the sedimentary radiocesium and the impact on the ecosystem near the seafloor remain unknown. In this presentation, we will give an overview of the distribution and behavior of $$^{137}$$Cs, especially on the seafloor along the coast of Fukushima, and report the latest results on the processes I the seafloor that should be considered on decadal timescale.

Oral presentation

Development of micro XAFS system at SPring-8 JAEA beamline BL22XU

Tanida, Hajime; Tsuji, Takuya; Kobata, Masaaki; Kitagaki, Toru

no journal, , 

In the decommissioning of Fukushima Daiichi Nuclear Power Plant, analysis of fuel debris is extremely important to understand its properties. The fuel debris to be removed on a trial basis and the samples available for analysis are expected to be fine particles. In the case of relatively large samples, handling becomes difficult due to the dose problem. Non-destructive X-ray analysis using X-rays, especially XAFS, is an effective analysis method for such samples, but in order to apply it to fine particles, X-rays must be focused to the micrometer order. For this purpose, a Kirkpatrick-Baez (KB) mirror was installed in the experimental hutch 3 of the RI building of the JAEA beamline BL22XU, which has a hard X-ray undulator as a light source, at SPring-8.

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