A study on natural radiation exposure in different realistic living rooms

摘要

In the first part of the paper, the factors affecting ~(222)Rn properties in 25 different realistic living rooms (with low ventilation rates) of different houses in El-Minia City (Upper Egypt) have been studied; they included the activity concentration of ~(222)Rn gas (C_o), the unattached fraction (f_p) of ~(218)Po and ~(214)Pb, the unattached potential alpha energy concentration (PAEC) and the equilibrium factor (F). The activity distributions of unattached ~(218)Po and ~(214)Pb as well as for the PAEC were determined. With a dosimetric model calculation [ICRP, 1994b. Human Respiratory Tract Model For Radiological Protection. Pergamon Press, Oxford. ICRP Publication 66] the total deposition fraction of unattached ~(218)Po and ~(214)Pb in human respiratory tract was evaluated to determine the total equivalent dose. An electrostatic precipitation method and a wire screen diffusion battery technique were both employed for the determination of ~(222)Rn gas concentration and its unattached decay products, respectively. The mean activity concentration of ~(222)Rn gas (C_o) was found to be 110 ± 20 Bq m~(-3). The mean unattached activity concentrations of ~(218)Po and ~(214)Pb were found to be 0.6 and 0.35 Bq m~(-3), respectively. A mean unattached fraction (f_p) of 0.09 ± 0.01 was obtained at a mean aerosol particle concentration (Z) of (2.9 ± 0.23) X 10~3 cm~(-3) The mean equilibrium factor (F) was determined to be 0.31 ± 0.02. The mean PAEC of unattached ~(218)Po and ~(214)Pb was found to be 8.74 ± 2.1 Bqm~(-3). The activity distributions of ~(218)Po and ~(214)Pb show mean activity median diameters (AMD) of 1.5 and 1.85 nm with mean geometric standard deviations (SD) of 1.33 and 1.45, respectively. The mean activity distribution of the PAEC shows an AMD of 1.65 nm with a geometric standard deviation of 1.25. At a total deposition fraction of about 97% the total equivalent dose to the lung was determined to be about 133 μSv. The second part of this paper deals with a study of natural radionuclide contents of samples collected from the building materials of the rooms under investigations in part one. Analyses were performed in Marinelli beakers with a gamma multichannel analyzer equipped with a NaI(Tl) detector. The samples revealed the presence of the uranium-radium and thorium radioisotopes as well as ~(40)K. Nine γ-lines of the natural radioisotopes corresponding to ~(212)Pb, ~(214)Pb, ~(214)Bi, ~(228)Ac, ~(40)K and ~(208)T1 were detected and measured. The activity concentrations of ~(226)Ra, ~(232)Th and ~(40)K were determined with mean activity concentrations of 58 ± 19, 31 ± 11 and 143 ± 62 Bq kg~(-1), respectively. These activities amount to a radium equivalent (Ra_(eq)) of 113 Bq kg~(-1) and to a mean value of external hazard index of 0.31.