ABSTRACT
Objective:To measure the influencing factors associated with the analysis of 226Ra gamma spectra in order to obtain more acurate and precise measuring result on a basis of further optimizing the gamma spectrometry method for 226Ra activity. Methods:A laboratory-based HPGe gamma spectrometer was used to carry out the studies on tracking measurement of sample sealing time, measurement of background fluctuation with lead shielding, analytical method, and selection of characteristic gamma ray energy peak of its daughter nuclides in 226Ra measurement. Results:After the sample was sealed for 12 d, the decay products of 226Ra- 222Rn basically reached equilibrium. The day and night fluctuations of 222Rn in the shielded lead room were obvious but had no obvious regularity. The way of filling nitrogen into the shielded lead room could reduce or avoid the influence of background fluctuations. For 31 soil samples measured after 23 days of sealing, the result of using the efficiency curve method showed that the 226Ra result calculated from the 351.9 keV energy peak were generally higher than the 609.3 keV energy peak, and the higher ratio ranged from 8.0% to 20.7%. The result of relative comparison method showed that the deviation ratio of the two peaks ranged from -4.1 % to 10.3 %. Conclusions:It is recommended to consider the uncertainty attributed from decay equilibrium about 4 % of measured at 12 d after the sample is sealed. When filling nitrogen through the shielded lead chamber to avoid background fluctuations, attention must be paid to the matching relationship between the volume of the lead chamber and the nitrogen filling flow. When the efficiency curve method is used to analyze the activity of 226Ra, the 214Bi ( 609.3 keV ) energy peak has the effect of cascade coincidence addition, so 214Bi(609.3 keV) energy peak should be avoided. When the relative comparison method is used to analyze the activity of 226Ra, both two energy peaks of 214Pb ( 351.9 keV ) and 214Bi ( 609.3 keV ) can be used.
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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.
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Objective To apply InSpector 1000 portable γ spectrometer and its corresponding supporting software to the monitoring of thyroid 131I activity of radiation workers, and to estimate the internal radiation dose of medical staff in nuclear medicine department. Methods The spectrometer was calibrated and taken to participate in the 2018 thyroid radioactive iodine intercomparison program initiated by Lawrence Livermore National Laboratory in the United States to ensure the accuracy of the measurement; the spectrometer was used to measure 131I activity ofthe radiation workers of the nuclear medicine departments of two grade-A tertiary hospitals in Beijing and Jinan to verify the feasibility of the method. Results The InSpector 1000 portable γ spectrometer was qualified for international intercomparison. Measurement results from the grade-A tertiary hospital in Beijing showed that the thyroid 131I activity of each of 10 radiation workers was below the detection limit (33.30 Bq). Measurement results from the grade-A tertiary hospital in Jinan showed that the thyroid 131I activities of the 4 radiation workers were 64.05 Bq, 160.77 Bq, 416.67 Bq, below the detection limit (35.18 Bq) respectively, and of 3 of the 4 subjects 131I was detected in the thyroid, and their corresponding thyroid accumulative organ doses were 0.70 μSv, 1.77 μSv, and 4.58 μSv, respectively. Conclusion InSpector 1000 portable γ spectrometer has a strong feasibility for thyroid 131I monitoring of radiation workers in nuclear medicine. The spectrometer has a good application prospect in the field of radiation monitoring, and can play an important role in the field of radiation protection and nuclear emergency detection.
ABSTRACT
Objective To explore the feasibility of using portable γ spectrometer to rapidly identify the low activity of depleted uranium and the underlying conditions.Methods Firstly,high purity germanium (Ge) γ spectrometer was used to analyze energy spectrum of DU samples (5 g) and calculate nuclide percentage of 235U in an attempt to ascertain the properties of these DU samples.The portable γ spectrometer was used to provide the evidences for identification of DU samples.Secondly,portable γ spectrometer was also used to identify DU samples of same group.These samples contain 1 g DU powder and 0-5 g environmental clay powder,which were sealed with double layer pocket,and then detected with a distance of 1-5 cm during the longest detection time of 10 min.According to the detection of nuclide activity of 238U and 235U in the samples and the subsequent calculation of specific activity,the nuclide percentage composition was calculated and the existence of DU was confirmed if this value of 235U was less than 0.718％.Results The activity of 238U was detected using portable γ spectrometer under all test conditions,while the activity of 235U was detectable only under certain test conditions (MA ≥ 1 g,DN ≤ 1 cm).Under the condition that the 238U and 235U was both detected,the nuclide percentage of 235U was all less than 0.718％,which suggested that the DU was confirmed.Conclusions The energy spectrum of low activity of DU and the type of nuclide could rapidly be identified and evaluated by using portable γ spectrometer.This is same as the conclusions obtained with high purity Ge γ spectrometer,α spectrometer and ICP-MS.