Uranium content in rocks by gamma-spectrometric and radiochemical methods is determined on the assumption of radioactive equilibrium between uranium and radium. Studies of the state of radioactive equilibrium in rocks are contradictory. Some researchers point to significant disturbances of radioactive equilibrium, while others point to the presence of equilibrium within the accuracy of the methods used to determine uranium and radium.

Radon and thoron are constituents of the Earth's atmosphere. The distribution of radon concentrations has been studied quite fully. There is much less information on thoron concentrations in the atmosphere. Significant daily and seasonal changes of radon concentrations in the surface layer of the atmosphere have been detected. The concentration of radon and thoron in atmospheric air is determined by their exhalation from rocks and soil, as well as by turbulent mixing in the atmosphere.