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KMID : 1039220190290020167
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Journal of Korean Society of Occupational and Environmental Hygiene
2019 Volume.29 No. 2 p.167 ~ p.175
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Characteristics of Internal and External Exposure of Radon and Thoron in Process Handling Monazite
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Chung Eun-Kyo
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Abstract
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Objectives: The purpose of this study was to evaluate airborne radon and thoron levels and estimate the effective doses of workers who made household goods and mattresses using monazite.
Methods: Airborne radon and thoron concentrations were measured using continuous monitors (Rad7, Durridge Company Inc., USA). Radon and thoron concentrations in the air were converted to radon doses using the dose conversion factor recommended by the Nuclear Safety and Security Commission in Korea. External exposure to gamma rays was measured at the chest height of a worker from the source using real-time radiation instruments, a survey meter (RadiagemTM 2000, Canberra Industries, Inc., USA), and an ion chamber (OD-01 Hx, STEP Co., Germany).
Results: When using monazite, the average concentration range of radon was 13.1-97.8 ㏃/㎥ and thoron was 210.1-841.4 ㏃/㎥. When monazite was not used, the average concentration range of radon was 2.6-10.8 ㏃/㎥ and the maximum was 1.7-66.2 ㏃/㎥. Since monazite has a higher content of thorium than uranium, the effects of thoron should be considered. The effective doses of radon and thoron as calculated by the dose conversion factor based on ICRP 115 were 0.26 m㏜/yr and 0.76 m㏜/yr, respectively, at their maximum values. The external radiation dose rate was 6.7 μ㏜/hr at chest height and the effective dose was 4.3 m㏜/yr at the maximum.
Conclusions: Regardless of the use of monazite, the total annual effective doses due to internal and external exposure were 0.03-4.42 mSv/yr. Exposures to levels higher than this value are indicated if dose conversion factors based on the recently published ICRP 137 are applied.
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KEYWORD
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dose conversion factor, effective dose, internal and external exposure, monazite, radon and thoron
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