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Health Phys. 1996 Mar;70(3):372-87.

High 222Rn levels, enhanced surface deposition, increased diffusion coefficient, humidity, and air change effects.

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  • 1International Academy of Hi-Tech Services, Inc., Annapolis, MD 21403, USA.


Measurements have been made of surface deposition rates for 218Po radon decay products in a small (0.283m3) aluminum test chamber for 222Rn levels from 1 to 1,600 kBq m-3. an increase in macroscopic surface deposition rate has been found to be induced by the high 222Rn concentrations. A distinct 222Rn level threshold has been found below which plateout is constant at the normal rate for ambient residential conditions. Above the threshold, an increase in plateout is observed and the transition quickly reaches a constant, higher plateout. With all environmental conditions remaining constant and varying humidity, the threshold 222Rn level decreases with increasing relative humidity. The rate of rise to the new plateau is found to increase with increasing humidity. For the constant air change rate of ACH = 0.2 h-1, the fraction of airborne 218Po lost by the enhanced plateout was consistently 0.4 +or- 0.25 for seven values of humidity from 8 to 54% RH. For a fixed RH = 40 +or- 2%, it was found that the threshold increases from 5 to 58 kBq m-3 for a change in ACH from 0 1.06 h-1. In converting the deposition data to values of diffusion coefficient D, using Crump and Seinfeld's theory, a very high D of 0.18 cm2s-1 is assumed for ambient air conditions. Results indicate an ambient D = 0.027 cm2s-1. The results may impact on research utilizing high levels in test chambers and diffusion coefficients and attached and unattached fractions, and also for cancer studies using animals with 222Rn levels as much as 10(4) times greater than ambient residential levels.

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