Research progress on radon migration in porous media.

Radon (222Rn), the only naturally occurring radioactive inert gas in the uranium decay chain, undergoes a multi-field coupled process of release and migration in porous media such as soil, rock and building materials. This paper reviews the emanation mechanisms (recoil, collision loss, particle geometry) and migration behaviours (diffusion, advection, relay transport) of radon, discusses the effects of intrinsic medium properties (nuclide abundance, pore structure, water content) and external environmental factors (temperature, wind speed, crustal stress, atmospheric pressure) on radon evolution, and summarises the progress in laboratory experiments, CFD numerical simulations, as well as the application achievements in indoor pollution control, mine safety monitoring, groundwater tracing and oil-gas exploration. Finally, the bottlenecks such as complex geological environment simulation, long-term cross-regional in-situ monitoring, and non-ideal multi-field coupled models are analysed, and future directions including cross-scale from micro to macro, development of smart sensors, and dynamic simulation of heterogeneous media are envisioned, providing scientific support for radiation protection and resource exploration.