Estimation of unattached and aerosol-attached activities of airborne short-lived radon progeny in indoor environments

Inhalation of the airborne short-lived radon progeny is regarded as the most crucial way of internal exposure to the natural radiation dose delivered to the human lung. In this respect, this study aims to determine the unat-tached and aerosol-attached activities of radon progeny and to estimate some important physical parameters employed to assess the radiological impact of this radiation on humans. For this purpose, radioactive aerosol samples collected on polycarbonate membrane filters to measure total alpha activity by passive alpha dosimetric technique using CR-39 detectors in sixteen different locations including some houses and workplaces in El Jadida city, in Morocco. In addition, the room-specific parameters and aerosol physical processes that affect the unat-tached and attached activity concentrations were determined. The obtained experimental results by the three-count method and room model parameters were used as input data on a developed PC-based software that we have developed to solve mathematical equations and calculate required physical quantities. Accordingly, the individual activities of radon progeny namely Po-218, Pb-214, and Po-214 as well as radon activity concentration were determined. Simultaneously, the unattached and aerosol-attached activity concentrations (C-j(u) and C-j(a)) of radon progeny were calculated based on the room model calculation. Consequently, some radiological quantities used in the calculation of the lung dose were estimated. The results showed that the indoor radon activity concentration in different targeted locations ranges between 38 and 143 Bq. m(-3) with an average value of 84.8 +/- 9.5 Bq. m(-3). The average obtained values of the equilibrium-equivalent concentration (C-eq), unattached fraction (f(p)), and equilibrium factor (F) at low and good ventilation rates change respectively from (24 Bq. m(-3), 0.08, and 0.25) to (34 Bq. m(-3), 0.02, and 0.41). Under normal environmental conditions, the average obtained values of C-eq, and F-p, in houses and at workplaces were (17 Bq.m(-3), 0.07, and 0.25) and (32 Bq. m(-3), 0.04, and 0.35) respectively. Depending on the different aerosol conditions and obtained values of unattached fraction fp, the calculated average values of dose conversion factors (DCFs) were 8.70 mSv.WLM-1 and 11 mSv.WLM-1 in houses and workplaces respectively. These values were in good agreement with the recommended values by ICRP, which are in the order of 9 mSv.WLM-1 and 12 mSv.WLM-1 for houses and workplaces respectively.