Refine your search:     
Report No.
Search Results: Records 1-20 displayed on this page of 182

Presentation/Publication Type

Initialising ...


Journal/Book Title

Initialising ...

Meeting title

Initialising ...

First Author

Initialising ...


Initialising ...


Initialising ...

Publication Year

Initialising ...

Held year of conference

Initialising ...

Save select records

JAEA Reports

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


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 $$^{14}$$C) and stable carbon ($$^{13}$$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 $$^{13}$$C (and stable nitrogen isotope, $$^{15}$$N) and $$^{14}$$C analyses; and $$^{13}$$C, $$^{15}$$N, and $$^{14}$$C measurements by the use of isotope ratio mass spectrometry and accelerator mass spectrometry (AMS). The guide briefly introduces ways to report $$^{14}$$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.

Journal Articles

Effectiveness of decontamination by litter removal in Japanese forest ecosystems affected by the Fukushima nuclear accident

Koarashi, Jun; Atarashi-Andoh, Mariko; Nishimura, Shusaku; Muto, Kotomi*

Scientific Reports (Internet), 10(1), p.6614_1 - 6614_11, 2020/04

 Times Cited Count:0 Percentile:100(Multidisciplinary Sciences)

We conducted a pilot-scale decontamination study in a deciduous broadleaved forest in Fukushima. The entire forest, other than two untreated areas, was decontaminated by removing the litter layer approximately 3.3 years after the accident. For three years after decontamination, we quantified $$^{137}$$Cs contamination levels in the litter and topsoil layers and in the tree leaves, in the untreated and decontaminated areas. The decreased inventories of litter-associated $$^{137}$$Cs in the decontaminated areas were observed only in the first year after decontamination. Generally, no decontamination effects were observed on the $$^{137}$$Cs transfer in tree leaves. The primary reason for this was the rapid shift in the main reservoir of $$^{137}$$Cs from litter layers to the underlying mineral soil, which differs from the observations in post-Chernobyl studies of European forest ecosystems. The results suggest that litter-removal decontamination can only be successful if it is implemented more quickly for Japanese forest ecosystems.

Journal Articles

Characterizing vertical migration of $$^{137}$$Cs in organic layer and mineral soil in Japanese forests; Four-year observation and model analysis

Muto, Kotomi; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Koarashi, Jun

Journal of Environmental Radioactivity, 208-209, p.106040_1 - 106040_10, 2019/11

 Times Cited Count:2 Percentile:52.23(Environmental Sciences)

Vertical distributions of $$^{137}$$Cs in the soil profile were observed at five forest sites with different vegetation types for 4.4 years after the Fukushima Dai-ichi Nuclear Power Plant accident, and $$^{137}$$Cs migration in the organic layer and mineral soil was analyzed based on a comparison of models and observations. Cesium-137 migration from the organic layer was faster than that observed in European forests, suggesting that the mobility and bioavailability of $$^{137}$$Cs could be suppressed rapidly in Japanese forests. The diffusion coefficients of $$^{137}$$Cs in the mineral soil were estimated to be 0.042-0.55 cm$$^2$$y$$^{-1}$$, which were roughly comparable with those of European forest soils affected by the Chernobyl Nuclear Power Plant accident. Model predictions indicated $$^{137}$$Cs mainly distributed in the surface mineral soil at 10 years after the accident. It suggest that the $$^{137}$$Cs deposited onto Japanese forest ecosystems will be retained in the surface layers of mineral soil for a long time.

Journal Articles

Effect of dry-wet cycles on carbon dioxide release from two different volcanic ash soils in a Japanese temperate forest

Nagano, Hirohiko; Atarashi-Andoh, Mariko; Koarashi, Jun

Soil Science and Plant Nutrition, 65(5), p.525 - 533, 2019/10

 Times Cited Count:1 Percentile:100(Plant Sciences)

In the present study, two volcanic ash soils (soil A and B) from a temperate broad-leaved forest in eastern Japan were incubated under repeated dry-wet cycles and continuously constant moisture conditions. The primary aims were to quantify the potential for enhancement of carbon dioxide (CO$$_{2}$$) release owing to increased water fluctuation and to examine differences in the responses of volcanic ash soils with different physicochemical properties. Soil B, rather than soil A, was a typical Andosol. During incubation at 20 $$^{circ}$$C for 120 days with five dry-wet cycles, the CO$$_{2}$$ release rate was measured periodically. Abundance of the stable carbon isotope in CO$$_{2}$$ ($$delta^{13}$$C-CO$$_{2}$$) was measured to capture changes in the origin of decomposed soil organic matter (SOM) owing to the dry-wet cycles. The CO$$_{2}$$ release rate under the dry-wet cycles was up to 49% higher than the values predicted from a parabolic relationship between CO$$_{2}$$ release and water content during incubation under the continuously constant moisture condition. The magnitude of CO$$_{2}$$ release enhancement was 2.7-fold higher in soil B relative to that in soil A. The $$delta^{13}$$C-CO$$_{2}$$ value in the dry-wet cycles was enriched by 0.3-2.3%$$_{0}$$ compared to that during incubation under the continuously constant moisture conditions, suggesting that the decomposition of old and/or well-metabolized SOM was enhanced by the dry-wet cycles. Thus, the present study suggests that Andosols, which have been believed to have a strong SOM stabilization ability, are vulnerable to dry-wet cycles. Then, increased water fluctuation in a future warmer world would have significant potential to stimulate CO$$_{2}$$ release from soils.

Journal Articles

A New perspective on the $$^{137}$$Cs retention mechanism in surface soils during the early stage after the Fukushima nuclear accident

Koarashi, Jun; Nishimura, Shusaku; Atarashi-Andoh, Mariko; Muto, Kotomi; Matsunaga, Takeshi*

Scientific Reports (Internet), 9, p.7034_1 - 7034_10, 2019/05

 Times Cited Count:11 Percentile:9.01(Multidisciplinary Sciences)

The aim of the present study is to explore the retention mechanisms of $$^{137}$$Cs in the surface soil layers of terrestrial ecosystems affected by the Fukushima NPP accident, with a specific focus on the interactions between $$^{137}$$Cs, soil minerals, and organic matter. Soil samples were collected from field, orchard, and forest sites in July 2011, separated into three soil fractions with different mineral-organic interaction characteristics. The results show that 20-71% of the $$^{137}$$Cs was retained in association with relatively mineral-free, particulate organic matter-dominant fractions in the orchard and forest surface soil layers. Given the physicochemical and mineralogical properties and the $$^{137}$$Cs extractability of the soils, $$^{137}$$Cs incorporation into the complex structure of particulate organic matter is likely the main mechanism for $$^{137}$$Cs retention in the surface soil layers.

Journal Articles

Low $$^{137}$$Cs retention capability of organic layers in Japanese forest ecosystems affected by the Fukushima nuclear accident

Koarashi, Jun; Atarashi-Andoh, Mariko

Journal of Radioanalytical and Nuclear Chemistry, 320(1), p.179 - 191, 2019/04

 Times Cited Count:5 Percentile:6.03(Chemistry, Analytical)

To quantify the $$^{137}$$Cs retention behavior in forest-floor organic layers in relation to the litter dynamics, litter samples were collected at five forest sites in Fukushima in 2011 and 2015, and separated into eight fractions with different precursor species and degrees of degradation; afterward, $$^{137}$$Cs inventory was determined in each litter fraction. The ecological half-lives of $$^{137}$$Cs in the litter fractions were estimated to be from 0.7 to 4.4 years and found to depend not on the sampling site but rather on the precursor species of the litter materials. Broadleaf- and pine-needle-originated litter fractions exhibited shorter ecological half-lives of $$^{137}$$Cs, while those of cedar-originated and finely fragmented litter fractions were longer. The results suggested that the organic layers in Japanese forest ecosystems have a low $$^{137}$$Cs retention capability, although it differs depending on the forest type.

Journal Articles

Radiocesium distribution in aggregate-size fractions of cropland and forest soils affected by the Fukushima nuclear accident

Koarashi, Jun; Nishimura, Shusaku; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Sato, Tsutomu*; Nagao, Seiya*

Chemosphere, 205, p.147 - 155, 2018/08

 Times Cited Count:7 Percentile:37.03(Environmental Sciences)

There is little understanding of how soil aggregation can affect the mobility and bioavailability of $$^{137}$$Cs in soils. To explore this, soil samples were collected at seven sites under different land-use conditions in Fukushima and were separated into four aggregate-size fractions. The fractions were then analyzed for $$^{137}$$Cs content and extractability and mineral composition. In forest soils, aggregate formation was significant, and $$^{137}$$Cs was largely associated with large-sized aggregates. In contrast, there was less aggregation in agricultural field soils, and most of $$^{137}$$Cs was in the clay- and silt-sized fractions. Across all sites, the $$^{137}$$Cs extractability was higher in the large-sized aggregate fractions than in the clay-sized fractions. The results demonstrate that large-sized aggregates are a significant reservoir of potentially mobile and bioavailable $$^{137}$$Cs in organic-rich (forest and orchard) soils.

Journal Articles

Fluctuation tendency of radioactive cesium in surface soil

Fujita, Hiroki; Maehara, Yushi; Nagaoka, Mika; Koarashi, Jun

KEK Proceedings 2017-6, p.35 - 39, 2017/11

no abstracts in English

Journal Articles

Sources of $$^{137}$$Cs fluvial export from a forest catchment evaluated by stable carbon and nitrogen isotopic characterization of organic matter

Muto, Kotomi; Atarashi-Andoh, Mariko; Koarashi, Jun; Takeuchi, Erina; Nishimura, Shusaku; Tsuzuki, Katsunori; Matsunaga, Takeshi*

Journal of Radioanalytical and Nuclear Chemistry, 314(1), p.403 - 411, 2017/10

 Times Cited Count:9 Percentile:11.84(Chemistry, Analytical)

Fluvial export of particulate and dissolved $$^{137}$$Cs was investigated to reveal its sources and transfer mechanisms in a broadleaved forest catchment using a continuous collection system. The finest size fraction ($$<$$ 75$$mu$$m), consisting of decomposed litter and surface mineral soil, was the dominant fraction in the particulate $$^{137}$$Cs load, although the contribution of coarser size fractions increased during high water discharge in 2014. The dissolved $$^{137}$$Cs originated from the decomposition of $$^{137}$$Cs-contaminated litter. Temporal changes in $$^{137}$$Cs distribution in the litter-mineral soil system indicated that the dissolved $$^{137}$$Cs load will be moderated in several years, while particulate $$^{137}$$Cs load has the potential to continue for a long time.

Journal Articles

Vertical distributions of global fallout $$^{137}$$Cs and $$^{14}$$C in a Japanese forest soil profile and their implications for the fate and migration processes of Fukushima-derived $$^{137}$$Cs

Koarashi, Jun; Atarashi-Andoh, Mariko; Amano, Hikaru*; Matsunaga, Takeshi

Journal of Radioanalytical and Nuclear Chemistry, 311(1), p.473 - 481, 2017/01

 Times Cited Count:11 Percentile:9.58(Chemistry, Analytical)

Vertical distributions of global fallout $$^{137}$$Cs and $$^{14}$$C were investigated in a Japanese forest soil in 2001. Even 38 years after the fallout, $$^{137}$$Cs was still observed mostly in the uppermost 5 cm. A preferential accumulation of $$^{137}$$Cs was found in a 1-cm-thick transition layer between organic-rich A and underlying B horizons. This unique observation indicated that $$^{137}$$Cs migrated through the A horizon at a rate of 0.20% y$$^{-1}$$ and the transition layer acted as a barrier for $$^{137}$$Cs migration to deeper layers. The vertical distributions of $$^{137}$$Cs and $$^{14}$$C were significantly correlated, suggesting a coupled downward migration of $$^{137}$$Cs and organic matter on a time scale of decades, along the same physical pathways.

Journal Articles

Post-deposition early-phase migration and retention behavior of radiocesium in a litter-mineral soil system in a Japanese deciduous forest affected by the Fukushima nuclear accident

Koarashi, Jun; Nishimura, Shusaku; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi

Chemosphere, 165, p.335 - 341, 2016/12

 Times Cited Count:20 Percentile:21.76(Environmental Sciences)

We established field lysimeters in a Japanese deciduous broad-leaved forest soon after the Fukushima nuclear accident to continuously monitor the downward transfer of $$^{137}$$Cs at three depths: the litter-mineral soil boundary and depths of 5 cm and 10 cm in the mineral soil. Observations were conducted at two sites within the forest from May 2011 to May 2015. Results revealed similar temporal and depth-wise variations in $$^{137}$$Cs downward fluxes for both sites. The $$^{137}$$Cs downward fluxes generally decreased year by year at all depths, indicating that $$^{137}$$Cs was rapidly leached from the forest-floor litter layer and was then immobilized in the upper (0-5 cm) mineral soil layer through its interaction with clay minerals. The decreased inventory of mobile (or bioavailable) $$^{137}$$Cs observed during early stages after deposition indicates that the litter-soil system in the Japanese deciduous forest provides only a temporary source for $$^{137}$$Cs recycling in plants.

Journal Articles

Forest type effects on the retention of radiocesium in organic layers of forest ecosystems affected by the Fukushima nuclear accident

Koarashi, Jun; Atarashi-Andoh, Mariko; Matsunaga, Takeshi; Sanada, Yukihisa

Scientific Reports (Internet), 6, p.38591_1 - 38591_11, 2016/12

 Times Cited Count:21 Percentile:23.38(Multidisciplinary Sciences)

Forest-floor organic layers play a key role in controlling the overall bioavailability of $$^{137}$$Cs in forest ecosystems; however, there is still an insufficient understanding of how forest types influence the retention capability of $$^{137}$$Cs in organic layers in Japanese forest ecosystems. Here we conducted plot-scale investigations on the retention of $$^{137}$$Cs in organic layers at two contrasting forest sites in Fukushima. In a deciduous broad-leaved forest, approximately 80% of the deposited $$^{137}$$Cs migrated to mineral soil located below the organic layers within two years after the accident, with an ecological half-life of approximately one year. Conversely, in an evergreen coniferous forest, more than half of the deposited $$^{137}$$Cs remained in the organic layers, with an ecological half-life of 2.1 years. The observed retention behavior can be well explained by the tree phenology and accumulation of $$^{137}$$Cs associated with litter materials with different degrees of degradation in the organic layers.

Journal Articles

Year-round variations in the fluvial transport load of particulate $$^{137}$$Cs in a forested catchment affected by the Fukushima Daiichi Nuclear Power Plant accident

Matsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 310(2), p.679 - 693, 2016/11


 Times Cited Count:5 Percentile:36.45(Chemistry, Analytical)

Particulate $$^{137}$$Cs in stream water was collected continuously for two years in order to assess the long-term trend of the $$^{137}$$Cs discharge from the forest environment. Sampling was conducted from December 2011 to December 2013 in a mountainous stream, which received the $$^{137}$$Cs from the Fukushima Daiichi Nuclear Power Plant accident. A seasonal increase in fluvial transport load of particulate $$^{137}$$Cs associated with suspended solids (SS) was observed in August and September when rainfall was abundant. The particulate $$^{137}$$Cs concentration decreased at a faster rate than the rate due to radioactive decay. This decrease might be resulted from redistribution of the easily eroded and polluted soil surface due to heavy rain events such as typhoons. These findings indicate that the particulate $$^{137}$$Cs load was subject to the inter-annual variations in rainfalls, and decreased gradually over a long period of time due to a decrease in $$^{137}$$Cs concentration in SS.

Journal Articles

Modeling dynamics of $$^{137}$$Cs in forest surface environments; Application to a contaminated forest site near Fukushima and assessment of potential impacts of soil organic matter interactions

Ota, Masakazu; Nagai, Haruyasu; Koarashi, Jun

Science of the Total Environment, 551-552, p.590 - 604, 2016/05

 Times Cited Count:21 Percentile:20.32(Environmental Sciences)

A model for $$^{137}$$Cs transfer in forest was developed to assess behavior of Fukushima-derived $$^{137}$$Cs. The model simulation well reproduced observed 3 year migration of $$^{137}$$Cs in organic layer and mineral soil. Long-term predictions indicated that more than 90% of the deposited $$^{137}$$Cs remains in the top 5 cm soil till 30 years, suggesting that forest acts as a long-term reservoir of $$^{137}$$Cs with limited loss via groundwater pathway. Impacts of soil organic matter (SOM) on $$^{137}$$Cs dynamics were investigated by modifying parameters of $$^{137}$$Cs turnover. The results showed that SOM-induced reduction of $$^{137}$$Cs adsorption, slower fixation of $$^{137}$$Cs by clay and enhanced mobilization of the fixed $$^{137}$$Cs elevate soil-to-plant transfer of $$^{137}$$Cs by increasing fraction of dissolved $$^{137}$$Cs. A substantial proportion (27% $$sim$$ 73%) of $$^{137}$$Cs in these soils was delivered to horizons deeper than 5 cm decades later. These results suggested that SOM significantly influences behavior of $$^{137}$$Cs over long-term.

Journal Articles

Atmospheric discharge of $$^{14}$$C from the Tokai reprocessing plant; Comprehensive chronology and environmental impact assessment

Koarashi, Jun; Fujita, Hiroki; Nagaoka, Mika

Journal of Nuclear Science and Technology, 53(4), p.546 - 553, 2016/04

 Times Cited Count:5 Percentile:36.45(Nuclear Science & Technology)

Quantitative evaluation of the atmospheric discharge of radiocarbon ($$^{14}$$C) is of primary importance for accurately assessing the radioecological impact of the operation of the Tokai reprocessing plant (TRP). However, monitoring the atmospheric $$^{14}$$C discharge was not conducted at the TRP prior to October 1991. The main purpose of this study was to establish the chronology of atmospheric $$^{14}$$C discharges for the entire operation period (1977-2014). We found strong correlation between the $$^{14}$$C discharge and spent fuel reprocessing data obtained after October 1991; we used this correlation to estimate the monthly $$^{14}$$C discharges in the 1977-1991 period. The total amount of atmospheric $$^{14}$$C discharge was estimated at 7741 $$pm$$ 217 GBq for the entire period. Tree-ring $$^{14}$$C analysis and model calculations using the established discharges were conducted to assess the excess $$^{14}$$C concentrations around the TRP in the past. The results indicated no significant radioecological impact of atmospheric $$^{14}$$C discharges from the TRP.

Journal Articles

Fluvial discharges of particulate and dissolved radiocesium from a forest and its monthly trend

Muto, Kotomi; Atarashi-Andoh, Mariko; Takeuchi, Erina; Nishimura, Shusaku; Koarashi, Jun; Tsuzuki, Katsunori; Nakanishi, Takahiro; Matsunaga, Takeshi

KEK Proceedings 2015-4, p.252 - 257, 2015/11

As a result of the Fukushima Daiichi Nuclear Power Plant accident, a large amount of radiocesium released into the atmosphere was deposited in forests. This study estimated the monthly trend in the fluvial discharges of radiocesium from a forest. The study site was a forested catchment in Kitaibaraki City. Radiocesium in river water was collected with a filtration system as both particulate and dissolved components. Filters and columns including dissolved Cs absorbent were replaced every month. The collected suspended solids were sieved into 2000-3000 $$mu$$m, 500-2000 $$mu$$m, 75-500 $$mu$$m, and $$<$$75 $$mu$$m fractions. The $$^{137}$$Cs concentrations in the samples were measured using $$gamma$$-ray spectrometry with Ge semiconductor detectors. The $$^{137}$$Cs discharge increased with the river water discharge. The particulate $$^{137}$$Cs discharge was dominant in both 2013 and 2014. The $$^{137}$$Cs discharge rate of the dissolved component increased in winter, when the river water discharge decreased.

Journal Articles

Catchment-scale distribution of radiocesium air dose rate in a mountainous deciduous forest and its relation to topography

Atarashi-Andoh, Mariko; Koarashi, Jun; Takeuchi, Erina; Tsuzuki, Katsunori; Nishimura, Shusaku; Matsunaga, Takeshi

Journal of Environmental Radioactivity, 147, p.1 - 7, 2015/09


 Times Cited Count:15 Percentile:40.7(Environmental Sciences)

We collected a large amount of radiocesium air dose rate data by mountain-walking with a small $$gamma$$-ray survey system, KURAMA-II, to create an air dose rate map of a mountainous deciduous forest that received radiocesium from the Fukushima Dai-ichi Nuclear Power Plant accident. Measurements were conducted in a small stream catchment 0.6 km$$^{2}$$ in size in August and September 2013, and the relationship between air dose rates and the mountainous topography was examined. Air dose rates increased with elevation, suggesting that more radiocesium was deposited on ridges, and that it had remained there for 2.5 years with no significant migration due to soil erosion or water drainage. Slope aspect also strongly affected air dose rates. By the continuous measurement using KURAMA-II, we describe the variation in air dose rates in a mountainous area and suggest that it is important to consider topography when selecting sampling points to estimating dose rates or contaminant deposition.

Journal Articles

A Passive collection system for whole size fractions in river suspended solids

Matsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; Nagao, Seiya*

Journal of Radioanalytical and Nuclear Chemistry, 303(2), p.1291 - 1295, 2015/02

 Times Cited Count:3 Percentile:62.51(Chemistry, Analytical)

An innovative, yet simple method for the passive collection of radioactive materials in river water has been developed and validated. The method employes large filter vessels, containing multiple cartridge filters. River water is led to the system naturally using a drop of the riverbed by hose from upstream. This method makes long-term, unmanned monitoring possible. In addition to regular radioactivity analyses, this method provides an opportunity for the characterization of suspended materials based on its ample collection quantities (more than several tens of grams). This method may also be applicable to sediment-bound chemicals.

Journal Articles

Topographic heterogeneity effect on the accumulation of Fukushima-derived radiocesium on forest floor driven by biologically mediated processes

Koarashi, Jun; Atarashi-Andoh, Mariko; Takeuchi, Erina; Nishimura, Shusaku

Scientific Reports (Internet), 4, p.6853_1 - 6853_7, 2014/10

 Times Cited Count:29 Percentile:23.29(Multidisciplinary Sciences)

The accident at the Fukushima Daiichi Nuclear Power Plant caused serious radiocesium ($$^{137}$$Cs) contamination of forest ecosystems located in mountainous and hilly regions with steep terrain. To understand topographic effects on the redistribution and accumulation of $$^{137}$$Cs on forest floor, we investigated the distribution of Fukushima-derived $$^{137}$$Cs in forest-floor litter layers on a steep hillslope in a Japanese deciduous forest in August 2013. Both leaf-litter materials and litter-associated $$^{137}$$Cs were accumulated in large amounts at the bottom of the hillslope. At the bottom, a significant fraction (65%) of the $$^{137}$$Cs inventory was observed to be associated with newly shed and less degraded leaf-litter materials, with estimated mean ages of 0.5-1.5 years, added via litterfall after the accident. Newly emerged leaves at the site were contaminated with Fukushima-derived $$^{137}$$Cs in May 2011 (two months after the accident) and $$^{137}$$Cs concentration in them decreased with time. However, the concentrations were still two orders of magnitude higher than the pre-accident level in 2013 and 2014. These observations are the first to show that $$^{137}$$Cs redistribution on a forested hillslope is strongly controlled by biologically mediated processes and continues to supply $$^{137}$$Cs to the bottom via litterfall at a reduced rate.

Journal Articles

Monitoring of airborne $$^{14}$$C discharge at RI facilities; A Comparison of collection and oxidation methods

Ueno, Yumi; Koarashi, Jun; Iwai, Yasunori; Sato, Junya; Takahashi, Teruhiko; Sawahata, Katsunori; Sekita, Tsutomu; Kobayashi, Makoto; Tsunoda, Masahiko; Kikuchi, Masamitsu

Hoken Butsuri, 49(1), p.39 - 44, 2014/03

The Japan Atomic Energy Agency has conducted a monthly monitoring of airborne $$^{14}$$C discharge at the forth research building (RI facility) of the Tokai Research and Development Center. In the current monitoring, $$^{14}$$C, which exists in various chemical forms in airborne effluent, is converted into $$^{14}$$CO$$_{2}$$ with CuO catalyst and then collected using monoethanolamine (MEA) as CO$$_{2}$$ absorbent. However, this collection method has some issues on safety management because the CuO catalyst requires a high heating temperature (600$$^{circ}$$C) to ensure a high oxidation efficiency and the MEA is specified as a poisonous and deleterious substance. To establish a safer, manageable and reliable method for monitoring airborne $$^{14}$$C discharge, we examined collection methods that use different CO$$_{2}$$ absorbents (MEA and Carbo-Sorb E) and oxidation catalysts (CuO, Pt/Alumina and Pd/ZrO$$_{2}$$). The results showed 100% CO$$_{2}$$ collection efficiency of MEA during a 30-day sampling period under the condition tested. In contrast, Carbo-Sorb E was found to be unsuitable for the monthly-long CO$$_{2}$$ collection because of its high volatile nature. Among the oxidation catalysts, the Pd/ZrO$$_{2}$$ showed the highest oxidation efficiency for CH$$_{4}$$ at a lower temperature.

182 (Records 1-20 displayed on this page)