Thermal diffusion of radon in porous media.
Based on the non-intersection model of cylindrical capillaries, the mean radius of the pores of some soils and building materials are estimated. In size, the above-mentioned radii are usually of the order of the free path of gas molecules at atmospheric pressure. A review of pore size distribution data also reveals that a large fraction of concrete pores belong to Knudsen's region. This fact indicates that the thermal gradient in these media must cause gas (radon) transport. The interpretation of the experimental data concerning the rate of emanation of 222Rn from a concrete-capped source subjected to a sudden increase in temperature is given, based on irreversible thermodynamics theory. The calculations given here for radon flux, caused by concentration and thermal gradients, are in satisfactory agreement with the experimental data. It is shown that thermodiffusion can significantly contribute to radon flux in concrete. The need to include the thermodiffusion radon flux in the radon entry model is discussed.
Minkin
L
L
Portland Community College, Physics Department, Sylvania Campus, ST 312, 12000 S.W. 49th Avenue, Portland, OR 97219, USA. lminkin@pcc.edu
D000396:Air Pollutants, Radioactive; D016902:Air Pollution, Indoor; D003252:Construction Materials; D004058:Diffusion; D005740:Gases; D006358:Hot Temperature; D015233:Models, Statistical; D011312:Pressure; D011886:Radon; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors
D000396:Air Pollutants, Radioactive; D005740:Gases; D011886:Radon