Evidence for nondiffusive transport of 86Rn in the ground and a new physical model for the transport

Abstract

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.