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Ochi, Kotaro; Funaki, Hironori; Yoshimura, Kazuya; Iimoto, Takeshi*; Matsuda, Norihiro; Sanada, Yukihisa
Radiation and Environmental Biophysics, 61(1), p.147 - 159, 2022/03
Times Cited Count：2 Percentile：44.25(Biology)Ji, Y.-Y.*; Ochi, Kotaro; Hong, S. B.*; Nakama, Shigeo; Sanada, Yukihisa; Mikami, Satoshi
Radiation Physics and Chemistry, 179, p.109205_1 - 109205_11, 2021/02
Times Cited Count：7 Percentile：70.8(Chemistry, Physical)In situ gamma-ray spectrometry using diverse survey platforms has been conducted in contaminated areas with several dose rate levels around the Fukushima Daiichi Nuclear Power Plant (FDNPP). Six survey sites, including two evacuation zones around the FDNPP, were selected for ground-based gamma-ray spectrometry using HPGe (high purity Ge) and LaBr
(Ce) detectors to assess the radioactive cesium deposition in the ground. The diverse levels of radioactivity of 
Cs were then distributed to six survey sites from 30 to 3000 kBq m
in the measurement period of October 2018. A method to directly calculate the depth profile using in situ measurement was introduced so as to have representation over a wide area, and the results were successfully compared with those of sample analysis at one point in the site.
-ray spectra obtained via aerial radiation monitoring using an unmanned helicopterOchi, Kotaro; Sasaki, Miyuki; Ishida, Mutsushi*; Hamamoto, Shoichiro*; Nishimura, Taku*; Sanada, Yukihisa
International Journal of Environmental Research and Public Health, 14(8), p.926_1 - 926_14, 2017/08
Times Cited Count：4 Percentile：22.46(Environmental Sciences)After the Fukushima Daiichi Nuclear Power Plant accident, the vertical distribution of radiocesium in soil has been investigated to better understand the behavior of radiocesium in the environment. The typical method used for measuring the vertical distribution of radiocesium is troublesome because it requires collection and measurement of the activity of soil samples. In this study, we established a method of estimating the vertical distribution of radiocesium by focusing on the characteristics of -ray spectra obtained via aerial radiation monitoring using an unmanned helicopter. In this method, the change in the ratio of direct rays to scattered rays at various depths in the soil was utilized to quantify the vertical distribution of radiocesium. The results show a positive correlation between the abovementioned and the actual vertical distributions of radiocesium measured in the soil samples.
Kurikami, Hiroshi; Malins, A.; Takeishi, Minoru; Saito, Kimiaki; Iijima, Kazuki
Journal of Environmental Radioactivity, 171, p.99 - 109, 2017/05
Times Cited Count：14 Percentile：45.59(Environmental Sciences)A modified diffusion-sorption-fixation model (mDSF) is proposed to describe the vertical migration of radiocesium in soils following fallout. The model introduces kinetics for reversible sites, meaning that the exponential-shape radiocesium distribution can be reproduced immediately following fallout. The initial relaxation mass depth of the distribution is determined by the diffusion length, which depends on the distribution coefficient, sorption rate and dispersion coefficient. The model captures the long tails of the radiocesium distribution at large depths. These tails are caused by different rates for kinetic sorption and desorption.
Amano, Hikaru; Onuma, Yoshikazu*
Journal of Radioanalytical and Nuclear Chemistry, 255(1), p.217 - 222, 2003/01
Times Cited Count：8 Percentile：49.8(Chemistry, Analytical)no abstracts in English
Amano, Hikaru; Watanabe, Miki*
The 5th Low Level Counting Conf. using Liquid Scintillation Analysis, 0, p.86 - 91, 1996/00
no abstracts in English
Matsuda, Norihiro; Mikami, Satoshi; Yamamoto, Hideaki; Saito, Kimiaki
no journal, ,
no abstracts in English
Cs) in forest soils after the Fukushima Dai-ichi Nuclear Power Plant accident; Observations and model analysisMuto, Kotomi; Atarashi-Andoh, Mariko; Koarashi, Jun; Matsunaga, Takeshi
no journal, ,
no abstracts in English
Kurikami, Hiroshi; Malins, A.
no journal, ,
Despite its affinity for binding to soil, radiocesium gradually migrates deeper into the ground over time. This results in a faster rate of reduction of air dose rates than would be expected by radioactive decay. Using radiation transport methods, this study calculated the trajectory of air dose rates over time given the evolution in the depth profile predicted by the model based on an advection-dispersion equation coupled with kinetic models of reversible/irreversible sorption. The results indicate a faster reduction in dose rates than the rate of radioactive decay in the first ten years following fallout, as there is a gradual migration of radiocesium in soil over this period. The rate of reduction of dose rates over the following years is then set by the rate of radioactive decay alone as the majority of the radiocesium has become fixed to the soil matrix.
Ochi, Kotaro; Sasaki, Miyuki; Ishida, Mutsushi*; Sanada, Yukihisa
no journal, ,
In previous studies, our group have developed the airborne radiation measurement (ARM) technique. We mounted a radiation detector under an unmanned aerial vehicle to evaluate the deposition of Fukushima accident-derived radiocesium over wide area. In this study, we performed ARM with mounting a LaBr(Ce) detector under an unmanned helicopter. A rapid and simple estimation of depth profile of radiocesium in soil was developed on the basis of the relationship between spectra obtained via ARM and actual depth profile of radiocesium. Our goal is same to series 1 that we attempt to achieve the advancement of airborne radiation measurement technique.
Matsuda, Norihiro; Mikami, Satoshi; Saito, Kimiaki
no journal, ,
no abstracts in English
Ochi, Kotaro; Yoshimura, Kazuya; Sanada, Yukihisa; Funaki, Hironori; Iimoto, Takeshi*
no journal, ,
The coefficient for converting from the air dose rate to a radiocesium inventory with relaxation mass depth (
) is proposed by Monte Carlo simulation. We confirm the validity of the conversion coefficient based on vertical distribution of radiocesium in soil and air dose rate obtained by contract research supported by the Nuclear Regulation Authority. The estimated radiocesium inventories based on air dose rate and values ( and 
) were defined as CI
and CI, respectively. Each CI were compared with integrated radiocesium inventory (MI) in soil samples. Good agreement was observed between CI and MI. This result suggested that the method for estimating radiocesium inventory based on and air dose rate is applicable to environment in Fukushima. By contrast, CI was overestimated compared with MI due to the trend of derived from difference of soil characteristics between Fukushima and Chernobyl.
Shimada, Asako; Tsukahara, Takehiko*; Nomura, Masao*; Takeda, Seiji
no journal, ,
Because of the accident at the Fukushima Daiichi Nuclear Power Station (1F), a large area of eastern Japan was contaminated by radiocesium. There are many old nuclear facilities in the area. When the old nuclear facilities will be decommissioned in three decades, the radioactive level of radiocesium from 1F would be more than clearance level. When radiocesium would be detected at the completion of their decommissioning in the site, estimation of the origin of which is from background originated 1F and fallout of atmospheric nuclear test or from decommissioned facilities will be important. Therefore, soils of 3 sites were collected by using U8 containers and by core boring, and Cs radioactivity, 
Cs/Cs radioactivity ratios, 
Cs/Cs isotope ratios were determined. Separation method of Cs from soil materials were developed based on the reported methods. The Cs radioactivity concentrations were varied in not only between sites but also in the same site, however, Cs/Cs radioactivity ratio was approximately constant in all sites. In case of highly contaminated soils, Cs/Cs isotope ratio was almost comparable to that for the soil collected at near the 1F. On the other hand, in case of lower contaminated soils, Cs/Cs isotope ratio was slightly higher than that for soil collected at near the 1F. It is possibly that fallout before the 1F accident contained Cs to increase the Cs/Cs isotope ratio. In the presentation, vertical distribution will also be discussed.
