| The radionuclides and radioactive gas of 222Rn,220Rn from the soil can cause radiation exposures to human beings. In this study, specific activity of natural radionuclides (235U,226Ra,210Pb,^Th and 40K) and artificial radionuclide (137Cs) and the concentrations of radioactive gas of 222Rn,220Rn in the urban soil samples, collected from the Third Ringroad area of Xi’an city, were measured using the high-resolution gamma spectrometer and RAD-7 solid state alpha electronic radon detector.The values of radionuclides specific activity and concentrations of radioactive gas of 222Rn,220Rn were measured in the studied soil samples. Pearson correlation analysis was applied to determine the interaction and relationships of the natural and artificial radionuclides concentrations, and radon gas of 222Rn,220Rn in soils. The characteristic of spatial distributions of radionuclides and 222Rn,220Rn in soils of Xi’an were analyzed based on the measured values using the geostatistics method. Radium equivalent activity (Raeq), the internal and external exposure indexes (Hin, Hex), absorbed gamma dose rate (D) and annual effective dose rate (AED) were calculated to evaluate the radiation risk level of Xi’an soil. Depending on the above studies, the main conclusions as follows:(1) The average specific activities of natural radionuclides 235U,226Ra,210Pb,232Th and 40K in Xi’an soil were 1.1,38.2,46.3,56.3 and 699.9 Bq kg-1, respectively. The average value of artificial radionuclide 137Cs was 0.8 Bq kg"1. The average values of the natural radionuclides 226Ra,232Th and 40K in Xi’an soil were slightly higher than those of Shaanxi, China and the world soil, respectively. The average specific activity of 226Ra in Xi’an soil was 1.1,1.2 and 1.2 times of Shaanxi, China and the world soil, respectively. For 232Th, the average value was 1.2,1.4 and 1.3 times of Shaanxi, China and the world soil, respectively. For 40K, the average value was 1.2,1.6 and 1.7 times of Shaanxi, China and the world soil, respectively. The average specific activity of artificial radionuclide 137Cs in Xi’an soil was less than other cities.(2) The average concentration values of soil radon gas of 222Rn and 220Rn, measured in the depth of 50cm from the soils, were 3233,6595 Bq m’3, respectively. The average value of the studied soil gas 222Rn was less than 10 OOOBq m-3, and it was in the low level compared with the reported values of other cities in China.Xi’an belongs to the low radon concentrations area and the soil radon concentrations range in the normal level.(3) The measured soil gas of 222Rn and 220Rn concentrations results showed different characteristics of spatial distribution in the studied area. For 222Rn, the high concentrations were measured in the east and northwest areas of the citiy, the low areas were found at the iner area of the Second Ringroad of Xi’an city. For 220Rn, the high concentrations were measured in the north and south areas.(4) Significant correlations of the natural and artificial radionuclides contents were found in Xi’an soil.222Rn and 220Rn concentrations in soil were also significantly correlated to the natural radionuclides contents.(5) The average values of Raeq, Hin, Hex, absorbed gamma dose rate and annual effective dose rate in the studied soil samples were 172.6 Bq kg-1,0.57,0.46,83.67 nGy h-1 and 0.10 mSv y-1, respectively. The average values of the evaluation indexes Raeq, Hin,Hex were much lower than the limit levels, respectively. The average values of absorbed gamma dose rate and annual effective dose rate were slightly higher than the worldwide representative values. |
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