| 210Pb is a highly toxic radionuclide with both radioactive and chemical toxicity,which can endanger human health in body.International Atomic Energy Agency and World Health Organization also set the strict concentration limits for 21oPb in food and drinking water.Therefore,there is important significance to measure and evaluate the level of 210Pb in environment and food accurately for radiation hygiene.As one of the important methods for measuring radionuclides,?-ray spectrometry has the advantages of simple preparation process and relatively short measurement time.It is suitable for rapid measurement of a large number of samples and widely used in measuring environment and food samples and emergency monitoring.However,the most of traditional ? spectrometers were coaxial P-type detectors with thick dead layer of the detector crystal,whose detective efficiency in low energy range was low.So,due to its low energy(46.5 keV)and small emission probability(4.25%),there was not much data reported for 210Pb measured by y spectroscopy.With the development of detector technology,the performance of some current detectors have been met the requirements for 210Pb measurement.But because of some characteristics in environment and food samples,such as diverse and strongly individual specificity,the self-absorption effect of the sample is serious and the degree of self-absorption effect is not constant.So,it was reported in previous literature that the pass rates of 210Pb in past international comparisons were low.To ensure the accuracy of the 210Pb measurement results,the individual specificity of the samples can not be ignored,which is also the difficulty of 7 spectrum measurement method for measuring 11rPb in environmental and food samples.Therefore,the purpose of this study is to establish a method for measuring the 210Pb activity level in environment and food samples with a gamma spectrometer.This measuring method can solve the current difficult problem for measuring 210Pb that is the individual specificity of the sample and take full advantage of y-ray spectrometry in process of sample preparation and measurement.In this study,a method for measuring 210Pb activity in environmental samples and food samples with a y spectrometer was developed.In the process of establishing the method,three standard calibration sources containing the known activity of 210Pb were first prepared,which could be dated back to national legal metrology department.The energy calibration of the Canberra BE5030 broad energy germanium(BEGe)y spectrometer and the detection efficiency of the samples were calibrated by the prepared standard calibration sources.Secondly,the models of Laboratory Sourceless Object Counting System(LabSOCS)were validated and optimized according to the efficiency calibrations acquired by corresponding standard calibration sources.After optimization,the maximum deviation between the efficiency value of LabSOCS and the corresponding efficiency from source was 4.29%.Then,the detection efficiency of the different samples was studied by LabSOCS software as an emphasis.The impact on detection efficiency of the ?-ray emitted by 210Pb,which is caused by the self-absorption effect of different samples,was evaluated,and the relevant self-absorption correction models were studied and discussed.More than 140 detection efficiencies of 210Pb were obtained by LabSOCS software.Those efficiencies of 210Pb were simulated from two kinds of container(cylinder sample container and Marinelli beaker)filled with more than 10 kinds of different matrix composition whose density was in a range from 0.50 g/cm3 to 3.00 g/cm3,respectively.And a self-absorption correction model was established based on this data.With the self-absorption correction model established,the detection efficiency obtained from the standard source can be corrected according to the density and matrix composition of every sample.Finally,the 210Pb measurement method established in this study was verified,and results of verification showed that this method could control the deviation of the measurement results within 5%.After the establishment of the measurement method,this method was used to measure the level of 210Pb activity in the environment and food samples.A total of 38 samples of air aerosol,2 samples of seabed sediment,5 samples of seafood and 3 samples of grain were measured and analyzed.The average 210Pb activity concentration of air aerosol was 878.7 }iBq/m3,and the results of 210Pb in the two seabed sediments were 59.42 Bq/kg and 114.91 Bq/kg.210Pb in 3 of the 5 seafoods can be detected.The specific activity was from 0.60 Bq/kg to 1.96 Bq/kg(fresh weight).And the specific activity of 210Pb in the grain(millet)samples ranged from 2.46 Bq/kg to 3.11 Bq/kg,which was higher than the default operational intervention level of 210Pb in food and drinking water(2 Bq/kg)recommended by International Atomic Energy Agency.From the work of measuring 210Pb in the environment and food samples,it was not only getting the data of 210Pb in detected samples,but also testing the feasibility of the 210Pb measurement method established in this study by practice.The method for measuring 210Pb activity developed by this study has considered the characteristics of environment and food samples,which makes it can get accurate results according to the self-absorption effect of the sample individual.This method can be applied in environment and food samples with a density from 0.50 g/cm3 to 3.00 g/cm3.It can enhance the accuracy of the measurement results and improve the quality of the data by measuring 210Pb activity in environmental samples and food samples with this method.This method can not only make the 21oPb data in the environment and food samples update quickly,but also grasp the 210Pb level in the environment and in food more accurately,which could provide more accurate base data for evaluation of environmental quality,food safety and public health related work. |
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