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KMID : 1151820170110050335
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Journal of the Korean Society of Radiology
2017 Volume.11 No. 5 p.335 ~ p.341
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Radioactivation Analysis of Concrete Shielding Wall of Cyclotron Room Using Monte Carlo Simulation
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Jang Dong-Gun
Lee Dong-Yeon
Kim Jung-Hoon
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Abstract
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Cyclotron is a device that accelerates positrons or neutrons, and is used as a facility for making radioactive drugs having short half-lives. Such radioactive drugs are used for positron emission tomography (PET), which is a medical apparatus. In order to make radioactive drugs from a cyclotron, a nuclear reaction must occur between accelerated positrons and a target. After the reaction, unncessary neutrons are produced. In the present study, radioactivation generated from the collisions between the concrete shielding wall and the positrons and neutrons produced from the cyclotron is investigated. We tracked radioactivated radioactive isotopes by conducting experiments using FLUKA, a type of Monte Carlo simulation. The properties of the concrete shielding wall were comparatively analyzed using materials containing impurities at ppm level and materials that do not contain impurities. The generated radioactivated nuclear species were comparatively analyzed based on the exposure dose affecting human body as a criterion, through RESRAD-Build. The results of experiments showed that the material containing impurities produced a total of 14 radioactive isotopes, and 60 Co(72.50%), 134 Cs(16.75%), 54 Mn(5.60%), 152 Eu(4.08%), 154 Eu(1.07%) accounted for 99.9% of the total dose according to the analysis having the exposure dose affecting human body as criterion. The 60 Co nuclear species showed the greatest risk of radiation exposure. The material that did not contain impurities produced a total of five nuclear species. Among the five nuclear species, 54Mn accounted for 99.9% of the exposure dose. There is a possibility that Cobalt can be generated by inducive nuclear reaction of positrons through the radioactivation process of 56 Fe instead of impurities. However, there was no radioactivation because only few positrons reached the concrete wall. The results of comparative analysis on exposure dose with respect to the presence of impurities indicated that the presence of impurities caused approximately 98% higher exposure dose. From this result, the main cause of radioactivation was identified as the small ppm-level amount of impurities.
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KEYWORD
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Cyclotron, Activation, impurities
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