Inhalation of 131I is the main route for internal doses to nuclear medicine workers. This study aimed to establish a simple analysis method for determining 131I activity in carbon cartridges, explore the activity concentration of 131I in nuclear medicine departments, and evaluate the internal dose of workers. A total of 21 nuclear medicine departments in the hospital conducted air sampling using a high-volume air sampler equipped with carbon cartridges and glass fiber filters to collect gaseous 131I and aerosol 131I, respectively. Furthermore, a mathematical model was developed to analyze the 131I activity with inhomogeneous distribution in cartridges. Based on the 131I activity measured by the HPGe γ spectrometer, the personal annual inhalation effective dose was estimated. The results showed that there is a significant difference in the activity of gaseous 131I and aerosol 131I, with the activity ranging from 1.5±0.08 Bq m-1 to 3,944.23±197.21 Bq m-3 and ND (not detectable) to 842.11±42.11 Bq m-3, respectively. The activity of aerosol 131I is about 1% to 7% of that of gaseous 131I. The annual committed effective dose caused by inhalation of 131I for workers is 3.6 μSv to 8.23 mSv, which is lower than the dose limit of 20 mSv y-1. In general, the 131I contamination in the nuclear medicine department cannot be ignored, and the concentration of 131I should be regularly monitored to prevent and control the internal radiation to which workers may be exposed.
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