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KMID : 0364920170420010033
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Journal of Radiation Protection and Research
2017 Volume.42 No. 1 p.33 ~ p.41
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The Transport Characteristics of 238U, 232Th, 226Ra, and 40K in the Production Cycle of Phosphate Rock
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Jung Yoon-Hee
Lim Jong-Myoung
Ji Young-Yong
Chung Kun-Ho
Kang Mun-Ja
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Abstract
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Background: Phosphate rock and its by-product are widely used in various industries to produce phosphoric acid, gypsum, gypsum board, and fertilizer. Owing to its high level of natural radioactive nuclides (e.g., 238 U and 226 Ra), the radiological safety of workers who work with phosphate rock should be systematically managed. In this study, 238 U, 232 Th, 226 Ra, and 40 K levels were measured to analyze the transport characteristics of these radionuclides in the production cycle of phosphate rock.
Materials and Methods: Energy dispersive X-ray fluorescence and gamma spectrometry were used to determine the activity of 238 U, 232 Th, 226 Ra, and 40 K. To evaluate the extent of secular disequilibrium, the analytical results were compared using statistical methods. Finally, the distribution of radioactivity across different stages of the phosphate rock production cycle was evaluated.
Results and Discussion: The concentration ratios of 226 Ra and 238 U in phosphate rock were close to 1.0, while those found in gypsum and fertilizer were extremely different, reflecting disequilibrium after the chemical reaction process. The nuclide with the highest activity level in the production cycle of phosphate rock was 40 K, and the median 40 K activity was 8.972 Bq·g -1 and 1.496 Bq·g -1 , respectively. For the 238 U series, the activity of 238 U and 226 Ra was greatest in phosphate rock, and the distribution of activity values clearly showed the transport characteristics of the radionuclides, both for the byproducts of the decay sequences and for their final products.
Conclusion: Although the activity of 40 K in k-related fertilizer was relatively high, it made a relatively low contribution to the total radiological effect. However, the activity levels of 226 Ra and 238 U in phosphate rock were found to be relatively high, near the upper end of the acceptable limits. Therefore, it is necessary to systematically manage the radiological safety of workers engaged in phosphate rock processing.
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KEYWORD
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Naturally occurring radioactive material (NORM), Phosphate rock, X-ray fluorescence spectrometry, Gamma spectrometry, Secular equilibrium
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