New observations in radon emanation and migration

An apparatus is built to observe radon emanation and migration under laboratory controlled conditions. The setup has a soil column as radon source, a chamber for continuous radon monitoring, and a closed loop with forced air circulation. Within this setup, radon levels are not affected by environmental factors. Radon only disappears through natural decay. Alpha recoil is the most important factor affecting the release of radon from mineral grains. Only those radon atoms produced near the surface of the grain, and recoil toward the surface have the chance of entering the pore space and migrating into the surrounding environment. Therefore, emanation power is related to particle surface area available for this release. A soil sample is collected and sieved to various sizes for radon emanation testing. Under this recoil-release model, one should expect that the radon level in the setup will increase as the particle size decreases. However, the authors discovered that the emanation power decreases with decreasing grain size. A new term, radon retention power, is proposed on the assumption that the negatively charged radon atom, due to alpha decay, could be retained on the surface of the same or another particle. This depends on the nature of the static charge of that particle. Radon levels in the setup are found to increase if the column is allowed to tilt down towards the monitor. As radon gas is approximately 7.5 times heavier than air, concentration of radon due to gravity is possible. This may explain the downward radon flux phenomenon in soil profiles observed by some investigators