Abstract: In order to quickly and accurately determine the pollution source terms for the decommissioning of uranium mines, and to solve the problems of long test cycle and cumbersome detection methods in the investigation process, the contaminated soil from uranium mines was used as research object in this paper. The decay characteristics under unbalanced conditions was analyzed, and the semi-infinite general source estimation model was used to calculate the γ dose rate of the surface concern points caused by the contaminated soil at different vertical depths. According to the dose rate contribution of uranium-series radionuclides and the effect on different vertical depths, the relationship between γ dose rate and radionuclide activity in soil surface layer was deduced. The results showed that the γ dose rate of the concern point caused by uranium series radionuclides is mainly contributed by the three daughters ^234mPa, ²¹⁴Bi and ²¹⁴Pb, which accounted for 96%. The dose rate of concern points caused by polluted radionuclides in the soil surface layer (20 cm) accounts for about 94%. According to the segmental equilibrium theory and the uranium- radium equilibrium coefficient, the characterization relationship between ²³⁸U and ²²⁶Ra as the representative radionuclides and the γ dose rate on the soil surface is deduced, compared with the actual monitoring results, the error was within ±5%. Based on this, the scope of the polluted soil could be quickly identified, the efficiency of source item investigation and monitoring distribution could be improved, and new ideas for scientific and objective in source item investigation of polluted soil could be provided.

Key words: uranium mine, contaminated soil, dose rate, radionuclide activity, characterization relationship