Radon and its isotopes are inert gases as they do not interact with any chemical compounds. Compared with thoron (220Rn) and radon-219 (219Rn), the risk of radioactive exposure of radon-222 (222Rn) is very high due to its long half-life of 3.8 d, while the half-life of 220Rn is 55 sec and of 219Rn is 4 sec. As a gas, radon can escape from the surfaces of ore, minerals, and rocks, then dissolve into groundwater and move very far from the formation site...