Radon exhalation and ultrafine fraction of radon progeny in closed room air

The influence of 222Rn exhalation from walls and air exchange (low ventilation rates ν<0.3 h-1) upon its concentration in room air has been considered. It was found that the radon concentration reachs 84 Bq m-3 at exhalation and ventilation rates of 66 Bq hm-2 and 0.28 h-1, respectively. The radon concentration and the ultrafine fraction fp of potential α energy concentration as well as the equilibrium factor F of the short-lived radon progeny were also determined in three different completely closed rooms. An electroprecipitation method was applied for determining the 222Rn concentration while a single wire-screen technique was used for the determination of ultrafine radon progeny. During the measurements, the radon concentrations were varied between 33 and 134 with a mean value 89 Bq m-3. A mean ultrafine fraction (fp) of 0.16 was obtained at a mean aerosol particle concentration (Z) of 1700 cm-3 and a mean equilibrium factor (F) of 0.33. The obtained mean value of fp was found to be about five times higher than the value reported in the ICRP publication (fp=0.03). The attachment rate (X), the deposition rate (qf) and the deposition velocity (vfd) of the ultrafine radionuclide 218Po were calculated. A mean value of X was found to be 49 h-1 at a mean qf of 46 h-1 and a mean vfd of 4.6 m h-1. The attachment coefficient β of 218Po was found to vary between 0.016 and 0.047 with a mean value 0.028 cm3 h-1.