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Journal Articles

Factors controlling dissolved $$^{137}$$Cs concentrations in east Japanese rivers

Tsuji, Hideki*; Ishii, Yumiko*; Shin, M.*; Taniguchi, Keisuke*; Arai, Hirotsugu*; Kurihara, Momo*; Yasutaka, Tetsuo*; Kuramoto, Takayuki*; Nakanishi, Takahiro; Lee, S*; et al.

Science of the Total Environment, 697, p.134093_1 - 134093_11, 2019/12

 Times Cited Count:8 Percentile:62.46(Environmental Sciences)

To investigate the main factors that control the dissolved radiocesium concentration in river water in the area affected by the Fukushima Daiichi nuclear power plant accident, the correlations between the dissolved $$^{137}$$Cs concentrations at 66 sites normalized to the average $$^{137}$$Cs inventories for the watersheds with the land use, soil components, topography, and water quality factors were assessed. We found that the topographic wetness index is significantly and positively correlated with the normalized dissolved $$^{137}$$Cs concentration. Similar positive correlations have been found for European rivers because wetland areas with boggy organic soils that weakly retain $$^{137}$$Cs are mainly found on plains. However, for small Japanese river watersheds, the building area ratio in the watershed strongly affected the dissolved $$^{137}$$Cs concentration.

Oral presentation

Performance of a new signal processing system for a detector array

Kimura, Atsushi; Koizumi, Mitsuo; Toh, Yosuke; Oshima, Masumi; Mizumoto, Motoharu; Goto, Jun*; Arai, Yasuo*; Sagara, Masahiro*; Iri, Shinichi*; Kobayashi, Hirotsugu*; et al.

no journal, , 

To measure neutron cross-section data of minor actinides, we construct a Ge-spectrometer utilizing multiple $$gamma$$-ray detection method. This spectrometer consists of 30 Ge crystals (40 detector outputs) and 128 BGO anti-Compton shields. Generally, a data acquisition system for such a big Ge spectrometer consists of many NIM modules; it requires large space and huge cost. To overcome these problems, we developed a new data acquisition system with digital signal processing techniques. We reported the conceptual design (and cost) in NSS 2004. In this NSS 2005, we report basic performance of this system (energy resolution, dead time and so on) and results of experiments with the Ge-spectrometer. We measured the energy resolution with a Eurisys clover detector, which is one component of the Ge-spectrometer. Obtained FWHMs (2.5 - 2.8 keV at 1.33 MeV) show good performances as normal MCA even with short shaping time and much higher channel density. The dead time of this system is only 3.2 micro sec per event.

Oral presentation

Effect of decontamination on the migrations of soil and radiocesium through river system

Taniguchi, Keisuke*; Kuramoto, Takayuki*; Onda, Yuichi*; Yoshimura, Kazuya; Arai, Hirotsugu*; Onuma, Saori*; Sato, Takayuki*

no journal, , 

no abstracts in English

Oral presentation

Study on residual charcoal particles contributed to outflow of radiocaesium from the site of wildfire to hydrosphere

Nomura, Naoki*; Arai, Hirotsugu*; Kuramoto, Takayuki*; Niizato, Tadafumi; Hayashi, Seiji*

no journal, , 

Wildfire in the mountainous forest of Fukushima, approximately 11 km west-north of the Fukushima Dai-ichi Nuclear Power Plant, burned 75 ha, which was occurred on 29th April and extinguished on 10th May 2017. In this study, we estimate the burning temperature and radiocesium elution characteristics of the residual carbides based on the thermal analysis and the dissolution test for the samples collected at the site of the wildfire to assess the impact of the wildfire on the radiocesium outflow.

Oral presentation

Effects on environmental dynamics of radiocesium related to the wildfire in mountainous forest of the Abukuma Mountains, Fukushima

Niizato, Tadafumi; Sasaki, Yoshito; Watanabe, Takayoshi; Mitachi, Katsuaki*; Ito, Satomi; Kuramoto, Takayuki*; Arai, Hirotsugu*; Nomura, Naoki*; Hayashi, Seiji*; Tamaoki, Masanori*

no journal, , 

$$^{137}$$Cs released from the TEPCO's Fukushima Dai-ichi Nuclear Power Plant accident has a long half-life of about 30 years, it is necessary to monitor the distribution and its radioecological impact over the long term. Mountainous forests, which accounts for about 70% of Fukushima prefecture, tend to be a sink of radiocesium contamination rather than a source for the contamination of other ecosystems. An understanding of the environmental dynamics of radiocesium in the forest floor of various conditions is important issue, while progressing to the resident return. In this paper, we report on the results of the field investigation into the $$^{137}$$Cs distribution and the $$^{137}$$Cs outflow in the mountainous forest of Fukushima, where the wildfire broke out in the spring of 2017.

Oral presentation

Study on carbonized temperature estimation of charcoal remained in burnt area in Namie Town, Fukushima

Nomura, Naoki*; Arai, Hirotsugu*; Kuramoto, Takayuki*; Niizato, Tadafumi; Hayashi, Seiji*

no journal, , 

In 2017, a wildfire occurred in mountainous forest of Namie Town, Fukushima Prefecture, where is designated as a difficult-to-return zone due to high radiation dose after TEPCO's Fukushima Daiichi Nuclear Power Plant accident. With the wildfire, changes of dynamics of radionuclide, especially Cs-137 was concerned. In this study, we focused residual charcoal to estimate burning temperature of surface soil and litter because it affects the dissolution behavior of nutrients and radiocesium in soil and litter on the forest floor of the burnt area. As a result of the wildfire, Japanese cedar forest and mixed forest with predominance of Japanese red pine and Japanese oak were burned, so we set up three control sites at each forest and collected the residual charcoals from burnt sites nearby unburnt locations. To clarify the carbonized temperature of residual charcoal, thermal analysis by TG-DTA and infrared adsorption spectrum analysis by micro-FTIR were conducted for litters, artificially burnt litters, and residual charcoals.

Oral presentation

Investigation of factors controlling dissolved $$^{137}$$Cs concentrations in Japanese rivers

Tsuji, Hideki*; Shin, M.*; Taniguchi, Keisuke*; Arai, Hirotsugu*; Kurihara, Momo*; Yasutaka, Tetsuo*; Kuramoto, Takayuki*; Nakanishi, Takahiro; Lee, S*; Shinano, Takuro*; et al.

no journal, , 

To predict the behavior of particulate and dissolved radiocesium ($$^{137}$$Cs) in river water, some soil and land use categories in the watershed should be considered because these may affect the dissolved $$^{137}$$Cs concentration. In this study, to investigate the factors that affect dissolved $$^{137}$$Cs concentrations in Japanese rivers, we measured dissolved $$^{137}$$Cs concentrations in 67 rivers under baseflow conditions 13-280 km from the Fukushima Daiichi Nuclear Power Plant in August and September 2017.

Oral presentation

Cesium-137 distribution and its transfer in mountain forest of Fukushima after the wildfire

Niizato, Tadafumi; Arai, Hirotsugu*; Hayashi, Seiji*

no journal, , 

The inventory of Cs-137 on the forest floor suffered from the wildfire in the Juman-yama region show no clear difference between the burnt and unburnt areas. The monitoring results of Cs-137 outflow from the mountain slope show high outflow rate one year after the wildfire, but restoration of forest floor cover results in the lower outflow rate next year after the wildfire.

Oral presentation

Environmental dynamics of radiocesium in the Fukushima environment

Niizato, Tadafumi; Hayashi, Seiji*; Arai, Hirotsugu*

no journal, , 

In this paper, we present an outline of Phase 1 investigation results and next Phase 2 research plans conducting in the Sector of Environmental dynamic research of Fukushima Prefectural Centre for Environmental Creation.

Oral presentation

Factors controlling dissolved $$^{137}$$Cs concentrations in east Japanese rivers

Tsuji, Hideki*; Ishii, Yumiko*; Hayashi, Seiji*; Shin, M.*; Taniguchi, Keisuke*; Arai, Hirotsugu*; Kurihara, Momo*; Yasutaka, Tetsuo*; Kuramoto, Takayuki*; Nakanishi, Takahiro; et al.

no journal, , 

Controlling factor of dissolved $$^{137}$$Cs concentrations in 66 in East Japan rivers was investigated. Dissolved $$^{137}$$Cs concentrations decreased by one order of magnitude between 2012 and 2017. Normalized dissolved $$^{137}$$Cs concentrations correlated well with building area ratios. Topographic wetness index generally predicted dissolved $$^{137}$$Cs concentrations. The high concentration of dissolved $$^{137}$$Cs in urban area cannot be explained by water quality condition.

Oral presentation

Estimation of the radiocaesium particle fraction in suspended sediment in river waters

Takeuchi, Yukio*; Taniguchi, Keisuke*; Arai, Hirotsugu*; Yoshita, Hirofumi*; Fujita, Kazuki*; Takahashi, Yusuke*; Kuramoto, Takayuki*; Nomura, Naoki*; Hagiwara, Hiroki; Dohi, Terumi; et al.

no journal, , 

no abstracts in English

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