Prediction of radon-silica systems in the Earth's mantle

Rn is a radioactive gas naturally produced in the Earth's crust that occurs in soils of different rock types. Cracking of rocks under pressure can affect the release of Rn, leading to an increase in atmospheric Rn concentrations. Hence, monitoring changes in Rn concentrations is important for predicting the geological activity. Silica is a major mineral in the Earth and super-Earth, and exploring the reaction between silica and radon has important implications for understanding the storage of radon in the mantle. Here, using crystal structure predictions and first-principles calculations, we have explored the reaction of radon gas with silica under the conditions of the mantle. The calculation results show that Rn and silica can form stable structures including Fd3̄m and P4₁ phases. These two phases exist in three regions including solid, partially diffused and liquid at high temperature and pressure. Under conditions of the Earth's mantle, the presence of RnSiO₂ systems means that silica can act as a reservoir for radon gas.