Nuclear Engineering and Technology

Korean Nuclear Society (한국원자력학회)
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Improvement of accuracy in radioactivity assessment of medical linear accelerator through self-absorption correction in HPGe detector

  • Suah Yu (Radiation Therapy Technology and Standards, Korea Institute of Radiological and Medical Sciences) ;
  • Na Hye Kwon (Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine) ;
  • Sang-Rok Kim (Radiation Safety Section, Korea Institute of Radiological and Medical Sciences) ;
  • Young Jin Won (Department of Radiation Oncology, Uijeongbu Eulji Medical Center, Eulji University) ;
  • Kum Bae Kim (Radiation Therapy Technology and Standards, Korea Institute of Radiological and Medical Sciences) ;
  • Se Byeong Lee (Proton Therapy Center, National Cancer Center) ;
  • Cheol Ha Baek (Department of Radiological Science, Kangwon Nation University) ;
  • Sang Hyoun Choi (Radiation Therapy Technology and Standards, Korea Institute of Radiological and Medical Sciences)
  • Received : 2023.09.18
  • Accepted : 2024.01.28
  • Published : 2024.06.25
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Abstract

Medical linear accelerators with an energy of 8 MV or higher are radiated owing to photonuclear reactions and neutron capture reactions. It is necessary to quantitatively evaluate the concentration of radioactive isotopes when replacing or disposing them. HPGe detectors are commonly used to identify isotopes and measure radioactivity. However, because the detection efficiency is generally calibrated using a standard material with a density of 1.0 g/cm3, a self-absorption effect occurs if the density of the measured material is high. In this study, self-absorption correction factors were calculated for tungsten, lead, copper, and SUS-303, which are the main materials of medical linear accelerator head parts, for each gamma-ray energy using MCNP 6.2 code. The self-absorption effect was more pronounced as the energy of the emitted gamma rays decreased and the density of the measured materials increased. These correction factors were applied to the radioactivity measurements of the in-built and portable HPGe detectors. Furthermore, compared to the surface dose rate measured by the survey meter, the accuracy of the measurements of radioactivity improved by an average of 124.31 and 100.53 % for inbuilt and portable HPGe detectors, respectively. The results showed a good agreement, with an average difference of 3.70 and 5.24 %.

Keywords

Acknowledgement

This research was supported by the National Research Foundation of Korea (NRF) grant (No.2020M2D9A309417021) & the Nuclear Safety Research Program through the Korea Foundation of Nuclear Safety (KoFONS) using the financial resource granted by the Nuclear Safety and Security Commission (NSSC) of the Republic of Korea (No.2205013) & National Research Council of Science & Technology (NST) grant by the Korean government (MSIT) (No. CAP22041-000).

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