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

We have measured the radon diffusion, solubility and permeability coefficie nts of various foils being of interest for the Borexino experiment. The app lied methods and instrumentation are described and the mathematical model f or diffusion of Rn, including its decay, is outlined. A very strong influen ce of water on the Rn diffusion through nylon foils was found. The rather l ow Rn permeability for dry nylon foil (mean value is equal to 3.35 x 10(-12 ) cm(2)/s) increases by more than two orders of magnitude if the foil is im mersed in water. No significant influence compared to dry nylon has been ob served if the foil was surrounded by pseudocumene. (C) 2000 Elsevier Scienc e B.V. All rights reserved.