Radon in ground water and soil as a potential tracer for uranium exploration and earthquake precursory studies

Radon, produced by radioactive decay of the trace amounts of uranium present in most rock is considered as a natural tracer for uranium exploration and studying earthquake precursory phenomena such as changes of radon concentration due to stress release from earth crust. Radon emitted from rocks containing uranium can partly dissolve and remain in ground water, subject to radioactive decay, until dispensed and aerated. Hence, a measurement of dissolved radon in ground water is a key path finder for uranium deposit. The paper discusses formulation and modeling of radon transport in soil media and its usefulness for interpretation of measured radon data with uranium deposit and stress release from earth crust. Analytical models were derived from basis radon transport theory of porous media considering diffusion as well as advection transport in addition to radon emanation and radioactive decay in the soil pore. Analysis of the model solutions indicates that radon monitoring in sub-soil is more reliable for stress release and earthquake precursory studies than deep soil sampling. On the other hand, radon monitoring in deep soil, preferably in ground water, can be applied for detecting the uranium deposit in certain areas. But it is necessary to measure ²²⁶Ra along with radon to compensate the contribution of radon from dissolved ²²⁶Ra in the water. The compensated radon activity is the actual indicator of ²²⁶Ra and uranium content in rocks at the vicinity of ground water source. Results of two experimental case studies were also presented to validate the above prediction of model. (author)