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Journal Articles

Research and development behind a computation system for 3D distributions of air dose rates in the environment; Estimating environmental radiation doses using PHITS together with remote sensing data

Kim, M.; Malins, A.; Sakuma, Kazuyuki; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

Isotope News, (765), p.30 - 33, 2019/10

Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The $$^{134}$$Cs and $$^{137}$$Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, individual conifer and broadleaf trees, and the topography of the land surface. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

Journal Articles

Development of an air dose rate evaluation system (3D-ADRES) for complex real environments in Fukushima Prefecture; Using remote sensing data and evaluating the influence of different features (topography, soil, buildings, trees, etc.)

Kim, M.; Malins, A.; Sakuma, Kazuyuki; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

RIST News, (64), p.3 - 16, 2018/09

To improve the accuracy of simulations for air dose rates over fallout contaminated areas, the distribution of the radionuclides within the environment should be modelled realistically, e.g. considering differences in radioactivity levels between agricultural land, urban surfaces, and forest compartments. Moreover simulations should model the shielding of $$gamma$$ rays by buildings, trees and land topography. Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The $$^{134}$$Cs and $$^{137}$$Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, based on nine common Japanese designs, individual conifer and broadleaf trees, and the topography of the land surface. Models are generated from Digital Elevation Model (DEM) and Digital Surface Model (DSM) datasets, and refined by users assisted with ortho-photographs of target sites. Completed models are exported from the system in a format suitable for the Particle and Heavy Ion Transport code System (PHITS) for the calculation of air dose rates and other radiological quantities. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

Journal Articles

Long-term predictions of ambient dose equivalent rates after the Fukushima Daiichi Nuclear Power Plant accident

Kinase, Sakae; Takahashi, Tomoyuki*; Saito, Kimiaki

Journal of Nuclear Science and Technology, 54(12), p.1345 - 1354, 2017/12

 Times Cited Count:5 Percentile:12.06(Nuclear Science & Technology)

Journal Articles

Analysis on the effect of forest decontamination on reducing the air dose rate using the three-dimensional transport code MCNP

Hemmi, Ko; Yamaguchi, Tetsuji; Takeda, Seiji; Kimura, Hideo

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 24(1), p.3 - 14, 2017/06

Conditions of contaminated sources and ranges of forest decontamination that significantly reduce the air dose rate in residential areas were investigated by means of a sensitivity analysis related to the decontamination of the forest contaminated by radiocesium deriving from the accident at Fukushima Daiichi Nuclear Power Station. The contaminated sources including $$^{134}$$Cs and $$^{137}$$Cs were assumed to be a layer of sedimented organic matter (the A$$_{0}$$ layer) and surface soils (the A$$_{1}$$ layer). The air dose rates were calculated using the three-dimensional Monte Carlo transport code MCNP. A slope number of the forest, angles, state of contaminant distribution, radiocesium content in the forest soils, decontamination ranges, distance from the forest boundary to an evaluation point, and height at the evaluation point were adopted as the parameters. The decontamination of a litter (A$$_{0}$$) layer within the distance of 20 m from the forest boundary was revealed to be effective in reducing the air dose rate when the source distribution was homogeneous. The air dose rates were significantly reduced by the decontamination of the A$$_{0}$$ layer within a distance of 40 m from the forest boundary on condition that the radiocesium content of the A$$_{0}$$ layer was larger than that of the A$$_{1}$$ layer and the source distribution was non-homogeneous, such as the forest areas beyond 20 m from the forest boundary, which were more heavily contaminated than those within 20 m.

Journal Articles

Evaluation of ambient dose equivalent rates owing to natural radioactive nuclides in eastern Japan by car-borne surveys using KURAMA-II

Ando, Masaki; Matsuda, Norihiro; Saito, Kimiaki

Nippon Genshiryoku Gakkai Wabun Rombunshi, 16(2), p.63 - 80, 2017/05

In order to discriminate the contribution of radioactive cesium due to the Fukushima Dai-ichi Nuclear Power Plant accident to the air dose rates measured by the car-borne surveys, natural background radiation was evaluated for eastern Japan area as the municipality averaged values. The window count method for distinction between natural and artificial radioactive nuclides was applied to the car-borne surveys using the KURAMA-II. Distribution of the evaluated natural background radiation showed geological feature, and it was found that the radiations measured along paved roads were reflecting the distribution of terrestrial $$gamma$$-rays. The effect of the radioactive cesium as of 2014 for the municipalities designated as the Intensive Contamination Survey Area was beyond the uncertainty of the natural background radiation. That for the other municipalities, however, was found to be almost negligible.

Journal Articles

Field test around Fukushima Daiichi Nuclear Power Plant site using improved Ce:Gd$$_{3}$$(Al,Ga)$$_{5}$$O$$_{12}$$ scintillator Compton camera mounted on an unmanned helicopter

Shikaze, Yoshiaki; Nishizawa, Yukiyasu; Sanada, Yukihisa; Torii, Tatsuo; Jiang, J.*; Shimazoe, Kenji*; Takahashi, Hiroyuki*; Yoshino, Masao*; Ito, Shigeki*; Endo, Takanori*; et al.

Journal of Nuclear Science and Technology, 53(12), p.1907 - 1918, 2016/12

 Times Cited Count:11 Percentile:6.81(Nuclear Science & Technology)

The Compton camera was improved for use with the unmanned helicopter. Increase of the scintillator array from 4$$times$$4 to 8$$times$$8 and expanse of the distance between the two layers contributed to the improvements of detection efficiency and angular resolution, respectively. Measurements were performed over the riverbed of the Ukedo river of Namie town in Fukushima Prefecture. By programming of flight path and speed, the areas of 65 m $$times$$ 60 m and 65 m $$times$$ 180 m were measured during about 20 and 30 minutes, respectively. By the analysis the air dose rate maps at 1 m height were obtained precisely with the angular resolution corresponding to the position resolution of about 10 m from 10 m height. Hovering flights were executed over the hot spot areas for 10-20 minutes at 5-20 m height. By using the reconstruction software the $$gamma$$-ray images including the hot spots were obtained with the angular resolution same as that evaluated in the laboratory (about 10$$^{circ}$$).

Journal Articles

Prediction of ambient dose equivalent rates for 30 years after the Fukushima accident and its technological development

Kinase, Sakae

Nippon Genshiryoku Gakkai-Shi, 58(6), p.362 - 366, 2016/06

no abstracts in English

Journal Articles

Changes in ambient dose equivalent rates around roads at Kawamata town after the Fukushima accident

Kinase, Sakae; Sato, Satoshi; Sakamoto, Ryuichi*; Yamamoto, Hideaki; Saito, Kimiaki

Radiation Protection Dosimetry, 167(1-3), p.340 - 343, 2015/11

 Times Cited Count:3 Percentile:53.75(Environmental Sciences)

Journal Articles

Outline of the national mapping projects implemented after the Fukushima accident

Saito, Kimiaki; Onda, Yuichi*

Journal of Environmental Radioactivity, 139, p.240 - 249, 2015/01

 Times Cited Count:20 Percentile:7.39(Environmental Sciences)

no abstracts in English

Journal Articles

Issue of air dose rate measurement using survey-meters

Tsuda, Shuichi; Saito, Kimiaki

"Fukushima No Fukko Ni Mukete No Hoshasen Ni Kansuru Korekara No Kadai" Shimpojiumu Hokokusho, p.30 - 33, 2015/00

Dose rate monitoring in air in the environment has been performed since the Fukushima Dai-ichi Nuclear Power Plant accident happened. The reliability of detectors such as survey-meters is ensured under a controlled set of standard conditions in a radiation calibration field. However, the calibration is performed only in a uniform irradiation condition in general, but in reality, the incident direction of the photons is random in the environment. Since detector responses are dependent on incident direction, except for spherical detectors, it is necessary to evaluate the reliability of the measured dose. In this study, using the PHITS code, dose rates in air of a common NaI(Tl) scintillation survey-meter and CsI(Tl) detectors used in the KURAMA system are calculated in a semi-infinite radiation field. In the presentation, the dependence of the dose rates on the incident direction of photons will be shown.

Journal Articles

Prediction of ambient dose equivalent rates for the next 30 years after the accident

Kinase, Sakae; Takahashi, Tomoyuki*; Sato, Satoshi*; Yamamoto, Hideaki; Saito, Kimiaki

Proceedings of International Symposium on Radiological Issues for Fukushima's Revitalized Future, p.40 - 43, 2015/00

To support recovery and rehabilitation in Fukushima, prediction models have been developed for ambient dose equivalent rate distribution within the 80 km-radius around the Fukushima Daiichi Nuclear Power Plant. The prediction models that are based on bi-exponential functions characterized by ecological half-lives of radioactive caesium for land-use, enable Fukushima residents to obtain distribution maps of ambient dose equivalent rates for the next 30 years after the accident. Model parameters were evaluated using ambient dose equivalent rates through car-borne surveys. The model parameters in deciduous and evergreen forest areas were found to be different from those in other areas. In addition, it was found that distribution maps of ambient dose equivalent rates for the next 30 years after the accident, created by the prediction models would be useful for follow-up of the radiological situation.

JAEA Reports

Study on measurement of spatial dose rates from simulated products made from recycled metal below clearance levels arising from dismantling of nuclear facilities (Contract research)

Okamoto, Akiko; Kitami, Yasuo*; Ando, Yoshiaki*; Nakamura, Hisashi; Saito, Kimiaki; Nakashima, Mikio

JAERI-Tech 2002-051, 40 Pages, 2002/06

JAERI-Tech-2002-051.pdf:3.63MB

In order to contribute to safety assessment of recycling products made from dismantling metal wastes, metal ingots containing $$^{60}$$Co were produced and spatial dose rates from the ingots were evaluated by gamma-ray measurement and calculation. Stripping operations were made using detector response functions calculated by Monte Carlo program to derive spatial dose rates from measured gamma-ray spectra. In the computer simulation, Monte Carlo and point kernel calculation codes were used. Agreement between measured and calculated values was satisfactory in spite of an extremely low concentration of $$^{60}$$Co in the ingots and a complicated geometric condition between detector and samples.

JAEA Reports

None

PNC-TJ1600 98-004, 50 Pages, 1998/03

PNC-TJ1600-98-004.pdf:1.63MB

no abstracts in English

JAEA Reports

None

PNC-TJ1600 97-002, 97 Pages, 1997/03

PNC-TJ1600-97-002.pdf:4.13MB

no abstracts in English

JAEA Reports

None

*; *

PNC-TJ1600 96-005, 52 Pages, 1996/03

PNC-TJ1600-96-005.pdf:1.4MB

no abstracts in English

JAEA Reports

None

*

PNC-TJ1600 96-003, 77 Pages, 1996/03

PNC-TJ1600-96-003.pdf:5.15MB

no abstracts in English

JAEA Reports

None

PNC-TJ1607 94-002, 60 Pages, 1994/03

PNC-TJ1607-94-002.pdf:2.52MB

no abstracts in English

JAEA Reports

None

PNC-TJ1545 91-001, , 1991/03

PNC-TJ1545-91-001.pdf:7.6MB

no abstracts in English

Oral presentation

Study on distribution and migration of radioactive substances around the Fukushima Daiichi Nuclear Power Plant, 8; Air dose measurement in living environment

Matsuda, Norihiro; Mikami, Satoshi; Nakano, Masakazu; Uno, Kiichiro; Hagiwara, Shigetomo; Yamamoto, Hideaki; Saito, Kimiaki

no journal, , 

no abstracts in English

Oral presentation

Study on distribution and migration of radioactive substances around the Fukushima Daiichi Nuclear Power Plant, 4; Measurement of air dose rate maps by a series of car-borne surveys

Ando, Masaki; Matsuda, Norihiro; Sato, Tetsuro*; Saito, Kimiaki

no journal, , 

A series of measurements of air-dose rate has been performed with a car-borne survey system KURAMA-II over wide areas in eastern Japan since 2011 to obtain data to grasp distribution of air dose rates and the decreasing tendency. Air dose rate maps were constructed by the seven car-borne surveys. It was found that the decreasing trend of air dose rates measured through car-borne surveys was found to be more pronounced than those expected on the basis of the physical decay of radioactive cesium and of the air dose rates measured using NaI (Tl) survey meters in the areas surrounding the roadways. In addition, it was found that the extent of decrease in air dose rates was moderated through the car-borne surveys performed in 2013.

60 (Records 1-20 displayed on this page)