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| 1.
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Nugraha, Eka Djatnika ; Hosoda, Masahiro ; Kusdiana ; Untara ; Mellawati, June ; Nurokhim ; Tamakuma, Yuki ; Ikram, Abarrul ; Syaifudin, Mukh ; Yamada, Ryohei ; Akata, Naofumi ; Sasaki, Michiya ; Furukawa, Masahide ; Yoshinaga, Shinji ; Yamaguchi, Masaru ; Miura, Tomisato ; Kashiwakura, Ikuo ; Tokonami, Shinji
概要:
Mamuju is one of the regions in Indonesia which retains natural conditions but has relatively high exposure to natural r
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adiation. The goals of the present study were to characterize exposure of the entire Mamuju region as a high natural background radiation area (HNBRA) and to assess the existing exposure as a means for radiation protection of the public and the environment. A cross-sectional study method was used with cluster sampling areas by measuring all parameters that contribute to external and internal radiation exposures. It was determined that Mamuju was a unique HNBRA with the annual effective dose between 17 and 115 mSv, with an average of 32 mSv. The lifetime cumulative dose calculation suggested that Mamuju residents could receive as much as 2.2 Sv on average which is much higher than the average dose of atomic bomb survivors for which risks of cancer and non-cancer diseases are demonstrated. The study results are new scientific data allowing better understanding of health effects related to chronic low-dose-rate radiation exposure and they can be used as the main input in a future epidemiology study.
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| 2.
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Omori, Yasutaka ; Hosoda, Masahiro ; Takahashi, Fumiaki ; Sanada, Tetsuya ; Hirao, Shigekazu ; Ono, Koji ; Furukawa, Masahide
概要:
The radiation doses from natural radiation sources in Japan are reviewed using the latest knowledge. The United Nations
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Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the Nuclear Safety Research Association report the annual effective doses from cosmic rays, terrestrial radiation, inhalation, and ingestion as natural sources. In this paper, the total annual effective dose from cosmic-ray exposure is evaluated as 0.29 mSv. The arithmetic mean of the annual effective dose from external exposure to terrestrial radiation is 0.33 mSv for the Japanese population using the data of nationwide surveys by the National Institute of Radiological Sciences. Previously in Japan, although three different groups have conducted nationwide indoor radon surveys using passive-type radon monitors, to date only the Japan Chemical Analysis Center (JCAC) has performed a nationwide radon survey using a unified method for radon measurements conducted indoor, outdoor, and in the workplace. Consequently, the JCAC results are used for the annual effective dose from radon and that for radon inhalation is estimated as 0.50 mSv using a current dose conversion factor. In this paper, UNSCEAR values are used for the mean indoor and outdoor thoron-progeny concentrations, and the annual effective dose from thoron is reported as 0.09 mSv. Thus, the annual effective dose from radon and thoron inhalation is 0.59 mSv. From a JCAC large-scale survey of foodstuffs, the committed effective dose from the main radionuclides in dietary intake is 0.99 mSv. Finally, the Japanese population dose from natural radiation is given as 2.2 mSv, which is similar to the reported global average of 2.4 mSv.
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| 3.
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Tamakuma, Yuki ; Yamada, Ryohei ; Iwaoka, Kazuki ; Hosoda, Masahiro ; Kuroki, Tomohiro ; Mizuno, Hiroyuki ; Yamada, Koji ; Furukawa, Masahide ; Tokonami, Shinji
概要:
In this study, a portable radioactive plume monitor using a silicon photodiode was developed for the detection of a radi
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oactive plume (e.g. ^<131>I, ^<134>Cs and ^<137>Cs) in an emergency situation. It was found that the background count rate was proportional to ambient dose equivalent rate and the detection limit for the monitor at 20 μSv h^<−1> as an ambient dose equivalent rate was evaluated to be 187 Bq m^<−3> using the ISO11929 method. These results suggest that the detection limit for the system can be decreased effectively by lead shielding with optimized thickness.
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| 4.
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Akata, Naofumi ; Kakiuchi, Hideki ; Tanaka, Masahiro ; Shima, Nagayoshi ; Shiroma, Yoshitaka ; Tokonami, Shinji ; Hosoda, Masahiro ; Ishikawa, Yoshio ; Furukawa, Masahide ; Sanada, Tetsuya
概要:
We have developed a rapid sampling system for measuring the tritium in atmospheric water vapor. The system consists of a
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high-efficiency particulate air filter cartridge, an oil-free compressor, a water-vapor-separating module with hollow fiber membranes, two cold traps, and an oil-free rotary pump. Compressed air (0.4 - 0.7MPa) is introduced into the water-vapor-separation module, which consists of a stainless steel column containing polyimide membrane tubes. Water vapor permeates through the tubes and is collected by cold traps cooled with dry ice and ethanol. The module is heated with a flexible heater to control its temperature. We have determined the recovery yields under various sampling conditions and find that this system can collect atmospheric water vapor with a recovery yield of >99%. This system can thus be a useful tool for understanding short-term observations of tritium in atmospheric water vapor.
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| 5.
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Akata, Naofumi ; Shiroma, Yoshitaka ; Furukawa, Masahide ; Kato, Akemi ; Kakiuchi, Hideki ; Hosoda, Masahiro ; Kanai, Yutaka ; Yanagisawa, Fumitaka
概要:
Aerosol samples were collected at Naha, Okinawa Prefecture, Japan during July 2001 to March 2005 to elucidate the concen
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trations of chemical components, including ^<210>Pb, present in air for a sub-tropical region of Japan. The NO^-_3, SO^<2->_4, NH^+_4 and Ca^+_2 concentrations had clear seasonal variations and were high in winter to spring and low in summer. ^<210>Pb concentrations ranged from 0.10 to 1.52 mBq m^<-3> and were low in summer and high in the other three seasons. The source of sulfur compounds in the aerosol samples was clarified by combining the sulfur isotope ratio δ^<34>S and ^<210>Pb concentrations. The multi-isotope method using δ^<34>S and ^<210>Pb concentrations was judged to be a good tool for understanding the transported sulfur source.
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| 6.
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城間, 吉貴 ; 城間, 勝人 ; 喜納, 正剛 ; 細田, 正洋 ; 安岡, 由美 ; 赤田, 尚史 ; 古川, 雅英 ; Shiroma, Yoshitaka ; Shiroma, Masato ; Kina, Seigou ; Hosoda, Masahiro ; Yasuoka, Yumi ; Akata, Naofumi ; Furukawa, Masahide
概要:
In order to understand the source of atmospheric radon concentration in the Gyokusendo which is the limestone cave on Ok
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inawa Island, the radon concentrations in the drip water from the ceiling were measured using a liquid scintillation counter. The arithmetic mean (± standard deviation) of radon concentration was 8.7 ± 2.0 kBq m^<-3>. This result suggests that the atmospheric radon in the cave was supplied from the drip water. When comparing the monthly precipitations which are considered to exert a profound influence on isotopic compositions of water seeping into a cave, the variation of radon concentration in the drip water was shown the delay of 60-90 days. The radon concentration in the soil water was estimated to be 47.3 kBq m^<-3>. Furthermore, the radon concentrations in the percolation water at the cave over a period of 9 to 10 days were calculated to be 9.3-7.7 kBq m^<-3>. The estimated radon concentration in the percolation water was almost equivalent with the measurement concentration in the drip water. These results suggest that the radon atoms in the drip water were generated from the soil above the cave. In other words, emanated radon from the soil particles might be the source of radon in the Gyokusendo.
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| 7.
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細田, 正洋 ; 赤田, 尚史 ; 下, 道國 ; 古川, 雅英 ; 岩岡, 和輝 ; 床次, 眞司 ; Hosoda, Masahiro ; Akata, Naofumi ; Shimo, Michikuni ; Furukawa, Masahide ; Iwaoka, Kazuki ; Tokonami, Shinji
概要:
岐阜県東濃地域において3″φ×3″NaI(Tl)シンチレーションスペクトロメータを用いた走行サーベイによって空気吸収線量率の測定を行った。逆距離荷重補間法によって東濃地域の空気吸収線量率の等値線図を作成した。土岐花崗岩及び苗木花崗岩地域の空
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気吸収線量率は領家帯花崗岩地域と比べて相対的に高い傾向を示した。東濃地域の6地点では，3″φ×3″NaI(Tl)シンチレーションスペクトロメータを用いて地表面から1mの高さにおけるγ線波高分布を取得した。得られたγ線波高分布の全てに^<134>Cs及び^<137>Csのフォトピークは観測されなかった。土岐市内の神社境内において最大で552nGy/hの空気吸収線量率，914Bq/kgの^<238>U系列濃度が観測された。
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| 8.
論文（リポジトリ） |
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細田, 正洋 ; 床次, 慎司 ; 古川, 雅英 ; Hosoda, Masahiro ; Tokonami, Shinji ; Furukawa, Masahide
概要:
自然界には多くの放射性核種が存在しており、われわれは常に自然放射線による被ばくを受けている。原子放射線の影響に関する国連科学委員会の2008年の報告書では、自然放射線による被ばく源を大地ガンマ線、ラドン、宇宙線および食物摂取に分類しており、
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ラドンによる被ばくが全体の約50％を占めている。しかしながら一般にはそのことが理解されておらず、平成23年3月11日に勃発した福島第一原子力発電所事故以降、国民の放射線被ばくに対する意識は一気に高まってきている。本稿では、主として大地ガンマ線やラドンに対するわが国の調査結果とそれによって評価された被ばく線量について概説し、さらに福島第一原子力発電所事故による外部被ばく線量の調査結果を報告する。
Various radionuclides are distributed in environmental materials such as soil, rock, and water. People are exposed every day to natural radiation.A ccording to the UNSCEAR 2008 report, Sources of Ionizing Radiation, natural radiation sources are categorized as terrestrial gamma-rays, radon, cosmic rays and food. The effective dose from radon, thoron and its decay products is about 50% of all natural radiation exposure. Consciousness of the Japanese public toward radiation exposure has significantly increased since the start of the Fukushima Dai-ichi Nuclear Power Station accident. In this paper, the nationwide survey and dose estimation for terrestrial gamma-rays and radon are summarized. External dose from artificial radionuclides released by the Fukushima accident are also reported. 論文 続きを見る |
