Investigation and analysis of radiation dose levels in a cyclotron room

Objective Levels and distribution of radiation dose in a cyclotron room were investigated to guide protection of personnel against radiation onsite and provide technical basis for the shielding design of workplaces with radioactive drugs. Methods A cyclotron HM-20S and the room in a hospital where it was installed were investigated.Several LiF (Mg, Cu, and P) thermoluminescence dosimeters, CR39 neutron dosimeters, a neutron dose equivalent rate meter NH-1B, and a dose survey meter 451 B were used to measure the neutron and gamma radiation dose rates in the cyclotron room. Radiation dose levels outside the room were also validated. Results When irradiation conditions were 20 MeV of proton energy and 100 μA of beam current, the maximum neutron dose rate from the southern surface of the self-shielding body of the equipment was 63 times higher than that from northern surface of the self-shielding body. Additionally, the maximum gamma-ray dose rate of the southern surface was 6.0 times higher than that of the northern surface. Neutron and gamma-ray dose rates measured on the inner surface of the southern wall were 11 and 5.3 times higher than those measured on the inner surface of the northern wall, respectively. In addition, mean values of neutron and gamma-ray radiation dose rates from the inner surface of the eastern wall were 21 and 45 μSv/h, correspondingly, whereas those from the western side were 34 and 69 μSv/h, respectively. Conclusion Levels and distribution of radiation dose in a cyclotron room are closely related to several factors, such as beam direction and target position. Radiation dose values measured onsite can be used to facilitate the shielding design of workplaces and provide radiation safety for personnel. Key words: Cyclotron; Cyclotron room; Radiation dose; Radiation protection