Online ISSN: 1884-4111 Print ISSN: 0033-8303
Radioisotopes 68(9): 595-603 (2019)


モンテカルロ計算を用いた原子力及び加速器施設における均等被ばく状況下での放射線業務従事者の被ばくの不均一性に関する検討γ線及びβ線による均等被ばく状況下での眼の水晶体への被ばくAssessment of Inhomogeneity of Exposure to Radiation Workers in Homogeneous Exposure Situations in Nuclear Industry and Accelerator Facility by Using Monte Carlo Calculations Coupled with a Mathematical PhantomExposure to the Lens of the Eye in Homogeneous Exposure Situation Due to Gamma and Beta Rays

日本原子力研究開発機構原子力科学研究所放射線管理部Department of Radiation Protection, Nuclear Science Research Institute, Japan Atomic Energy Agency ◇ 319–1195 茨城県那珂郡東海村大字白方2–4 ◇ 2–4 Shirakata, Tokai-mura, Naka-gun, Ibaraki 319–1195, Japan

受付日:2019年2月12日Received: February 12, 2019
受理日:2019年4月15日Accepted: April 15, 2019
発行日:2019年9月15日Published: September 15, 2019

国際放射線防護委員会(ICRP)勧告では,放射線業務従事者の眼の水晶体等価線量限度が現在の限度である一年あたり150 mSvから5年平均で年間20 mSvに大幅に引き下げられた。本稿では,原子力及び加速器施設で放射線業務従事者が通常受ける,均等被ばく状況に着目し,従事者の水晶体線量の体幹部で測定される線量との違いについて評価した。その結果,β線の場合,体幹部での70 μm線量当量の測定値から推定する場合,眼の水晶体等価線量を4倍程度過大評価することが示された。

The recommended annual limit of equivalent dose to the lens of the eye has decreased to 20 mSv y−1 from the current limit of 150 mSv y−1. In terms of occupational exposure to radiation workers, exposure inhomogeneity plays an important role when estimating equivalent dose to the eye lens from readings of dosimeters worn by workers on their trunk. The authors focused on homogeneous exposure situations that radiation workers may encounter in nuclear and accelerator facilities. Moreover, the authors investigated how radiation workers are exposed non-homogenously in homogeneous exposure scenarios, where radiation workers may usually be encountered, regardless of their radiation works. In our previous study, we proposed a methodology to quantitatively evaluate the inhomogeneity of exposure. The homogeneity of exposure was evaluated by performing Monte Carlo calculations with a mathematical phantom under the isotropic and rotational irradiation geometries due to gamma and beta rays. Hp(3)eye/Hp(10)trunk exceeded 1.0 even in the case of homogenous exposure to gamma rays. Even in the homogeneous exposure scenarios, the Hp(3)eye might exceed the revised annual dose limit for radiation workers who are exposed close to annual dose limit. For exposure due to beta rays from 90Y, the equivalent dose of the lens of the eye might overestimate around four times when estimated from the Hp(0.07) measured on worker’s trunk.

Key words: eye lens dose; Hp(3); occupational exposure; radiation protection; Monte Carlo calculation

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