Characterization of radon gas transmission rate in pore structures of different rock layers by radon daughters inversion calculation

Determining the transmission rate of radon gas in overburden strata is crucial for conducting a comprehensive study of radon gas's longitudinal and long-distance migration mechanisms. This study investigates the mineral components of rocks in the underground strata of the mining area using the X-ray diffraction method. Additionally, it examines the pore structure parameters of the rocks at different depths using the low-temperature nitrogen adsorption method. This research introduces an approach to inversion calculate the radon gas transmission rate through the activity ratio of radon's characteristic daughters based on the decay law and activity balance of ²¹⁰Po and ²¹⁰Pb daughters. In addition, it determines the transmission rates of radon gas in overlying strata at various depths through this method. The relationship between the rock's mineral composition and pore structure is investigated, and the effects of pore structure and mineral composition on the radon gas transmission rate are analyzed. The findings indicated that the pore structure exerts a dual impact on radon gas transport: macropores serve as channels for upward radon gas transport, while micropores offer most of the adsorption area. In contrast, the radon gas transmission rate is indirectly influenced by the mineral composition content associated with the medium's adsorption capacity and pore structure. In the studied lithologies, an increase in quartz content promotes radon gas transmission, while an increase in clay mineral content impedes it. Finally, the mechanisms of radon gas transport, daughter adsorption, and the impacts of rock pore structure and mineral composition on the radon transmission rate are discussed.