Concentration of radon has been measured in the soil near the ground surface with solid-state, nuclear track detectors with the inverted cup technique. Measurements were made in the overburden at depth intervals 0.1-0.7 m, at 0.1-6 m, and at a constant depth of 0.2 m, in a narrow rectangular matrix. The results disagree with the hypothesis that radon concentration only depends upon local production and migration by diffusion with a diffusion length of about 1 m. A transport length of 0.1-0.2 m is observed near the ground surface and the transport is dominated by a flow component.Radon measurements in the ground surface over the Laisvall lead mine have given evidence of radon transport through rock exceeding a distance of 100 m, which is possible only if the migration is a flow transport with a characteristic transport length larger than about 10 m/day.To explain the radon transport in the overburden and through the rock with a common transport system, the existence of a general upward flow of geo-gas is proposed. This geo-gas works as a carrier mechanism for radon. The physical conditions for the existence of a flow transport of radon are discussed.

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