ABSTRACT
Exposure to ionizing radiation inside houses, especially radionuclides of radon and its progeny, poses serious health risks that can be exacerbated when inhaled as a result of interaction with human lung tissue. Also, air ionization is mainly due to these radionuclides. Therefore, accurate measurements of radon activity concentrations and its short-lived progeny are required to assess dose and environmental pollution and estimate ionization rates in indoor environments. For this purpose, we employed a previously tested and approved reliable method, following the three-count procedure. This method is based on airborne radon progeny sampling on polycarbonate membrane filters and alpha counting using a passive α-dosimetry technique with CR-39 detectors. The method also relies on a PC-based software we developed for solving mathematical equations and calculating all the necessary physical quantities. In this study, the concentrations of radon and individual short-lived radon progeny were measured in 20 houses in Sana'a, Yemen. Measurement conditions and meteorological variables were considered. The average activity concentrations of 222Rn, Equilibrium-Equivalent Concentration (EEC), 218Po, 214Pb, and 214Po were 73.1 ± 6.0, 29.2 ± 2.4, 44.4 ± 3.6, 30.5 ± 2.5, and 23.2 ± 1.9 Bq.m-3, respectively. The calculated average unattached fractions f1(218Po), f2(214Pb), and fp were found to be 0.24, 0.04, and 0.07 % respectively. The annual average values of ion-pair production rate caused by 222Rn and their progeny and air ion concentration, were 27.25 ions.cm-3s-1 and 1829 ions.cm-3 respectively. The annual effective dose was estimated to be 1.93 ± 0.16 mSv.y-1, well lower than the recommended 10 mSv.y-1.
ABSTRACT
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 unattached 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 unattached 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 218Po, 214Pb, and 214Po as well as radon activity concentration were determined. Simultaneously, the unattached and aerosol-attached activity concentrations (Cju and Cja) 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 (Ceq), unattached fraction (fp), 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 Ceq, fp, and F, 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.
