ABSTRACT
Objective:To investigate the differences in applicability of both the portable high-purity germanium (HPGe) γ spectrometer and the portable lanthanum bromide (LaBr) γ spectrometer for measuring thyroid 131I activity and internal exposure monitoring for radiation workers. Method:Both DETECTIVE-DX100-KT portable HPGe γ spectrometer and InSpector 1000 portable LaBr γ spectrometer were used to measure the 131I content in thyroid of radiation workers for comparison of the measuring result, minimum detectable activity (MDA) and corresponding annual committed effective doses between two types of spectrometers. Results:The detection rate of 131I in thyroid of radiation workers was 67.7% for HPGe γ spectrometer and 26.2% for LaBr γ spectrometer, respectively. The MDA was 12.26-14.74 Bq (measuring time: 3-5 min) for HPGe γ spectrometer and 56.56-80.37 Bq for LaBr γ spectrometer (measuring time: 2-4 min). The annual committed effective dose corresponding to MDA was 0.07-0.08 mSv (3-5 min) for HPGe and 0.31-0.45 mSv (2-4 min) for LaBr, respectively, in the case of using chronic continuous intake mode and 7 d monitoring period. Conclusions:The minimum detectable activity (MDA) of the two types of portable spectrometers could meet the requirements specified in GBZ 129-2016 Specifications for individual monitoring of occupational internal exposure for thyroid monitoring equipment. The two types of spectrometers could be used for routine monitoring of internal contamination. The difference between the monitoring result of LaBr γ and HPGe γ spectrometers might be due to such factors as large uncertainty in short measuring time and low activity concentrations, incomplete identical of distance between probe and neck, probe angle setting, different response of equipment to the environment, background deduction method.
ABSTRACT
Objective:To explore the assessment methodology for internal dose to workers exposed to 131I radionuclide. Methods:Workers were chosen in a 131I radiopharmaceutial manufacturer and a nuclear medicine department in a hospital using 131I to treat hyperthyroidism and thyroid cancer. A portable high purity germanium (HPGe) gamma spectrometer was used to measure the content of 131I in the thyroid for 4 consecutive times in a period of 7 d. The internal dose was estimated combining with the work rotation mode for workers dealing with 131I. Results:When the monitoring month was used as a typical month to estimate the internal dose, the annual committed effective dose was 0.09-1.93 mSv for the production staff engaged in the repackaging of 131I radiopharmaceuticals in the surveyed enterprise, and 0.06-0.58 mSv for the nuclear medicine staff in the surveyed hospital. After adjusting the monitoring result of the current monitoring period based on the rotation mode, the annual committed effective dose was estimated to be 0.06-1.22 mSv for radiopharmaceutical production workers and 0.03-0.15 mSv for nuclear medicine workers, respectively. Conclusions:In the assessment of internal dose to radiation workers exposed to 131I, using a single time measurement result to estimate the annual dose would lead to a larger error. In the case of continuous monitoring, the result of subsequent monitoring periods should be corrected according to the result of previous monitoring periods. In order to accurately estimate the internal dose of workers exposed to 131I, it is necessary to take full account of the 131I exposure pattern, time and frequency and the internal contamination route. For workers who may be exposed to 131I with potential internal dose greater than 1 mSv/year, a 14 day-routine monitoring period was appropriate.