Radon diffusion through polymer membranes used in the solar neutrino experiment Borexino

We have measured the radon diffusion, solubility and permeability coefficients of various foils being of interest for the Borexino experiment. The applied methods and instrumentation are described and the mathematical model for diffusion of Rn, including its decay, is outlined. A very strong influence of water on the Rn diffusion through nylon foils was found. The rather low Rn permeability for dry nylon foil (mean value is equal to 3.35×10−12 cm2/s) increases by more than two orders of magnitude if the foil is immersed in water. No significant influence compared to dry nylon has been observed if the foil was surrounded by pseudocumene.