The Research On The Evaluation Of Urban Environmental Natural Radioactivity

This paper is based on the project of "The Study of Radon Radiation Field and Environmental Effect on the Air-Ground Interface", financed by the National Natural Science Foundation of China (NO: 40374051), and "The Urban Ecology and Geochemistry Evaluation of Chengdu Economic Region", financed by Chinese Geology Survey (NO: 200314200015). The methods of urban environment's natural radioactivity were investigated through abundances of experiments and field measurements. Based on the data of Geochemistry and the model of U-Ra equilibrium, the natural radioactivity's level of Chengdu has been analyzed and evaluated, and got some conclusions as follows:(1) The survey method for urban environmental radioactivity has been developed, by mean of theoretically and experimentally investigating the influence of urban building on the urban natural radioactivity;(2) The model of U-Ra equilibrium was created by means of the correcting of the content of ²²⁶Ra and ²³⁸U in soil, thereby it supplied the mathematic model for the gamma exposure rate of natural radioactivity in Chengdu;(3) By analyzing the content of natural radioactive nuclides in soil, it could be conclude that the external exposure index in Chengdu is between 0.35 and 0.7; the internal radiation is between 0.17 and 0.31; the frequency is above 90% of gamma exposure rate between 70nGyh^-1 and 110 nGyh^-1, and effective dose is between 0.38mSv and 0.55mSv, which is in normal level.(4) The average of the gamma exposure rate in the western Chengdu is higher than the eastern area 10nGyh^-1, which is caused by the fracture zone of Shuangliu-Chengdu-Deyang. The measurement results show that the external exposure index and gamma exposure rate in the near fracture zone is obviously higher than other area. Moreover coil-fire power plant will also increase the radioactivity level in its near area.