ACTIVITY OF ULTRAFINE FRACTION OF RADON PROGENY IN INDOOR AIR

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1 Journal of Nuclear and Radiation Physics, Vol. 8, No. 1&2, pp ACTIVITY OF ULTRAFINE FRACTION OF RADON PROGENY IN INDOOR AIR A. Mohamed, M. Yuness, M. Abd El-Hady and Mona Moustafa Department of Physics, Faculty of Science, Minia University, Minia, Egypt and Rec. 05/01/2013 Accept.10/12/2013 Inhalation of 222 Rn progeny has been recognized as a health risk, primarily as a cause of human lung cancer. 222 Rn progeny in the domestic environment contributes the greatest fraction of the natural radiation exposure to the public. The ultrafine activity of these progeny amounts up to about 10 percent of the total activity (attached and ultrafine), but is considered to yield about 50 percent of the total radiation dose. Therefore, measurements of ultrafine fraction are essential for the estimation of radiation dose. The current study presents measured data on the total equilibrium equivalent concentration (EEC) and ultrafine equilibrium equivalent concentration ( EEC un ), ultrafine fraction (f b ), and unattached activity size distributions of radon progeny in the low ventilated room at Minia University, Minia City, Egypt. A screen diffusion battery was used for collection the ultrafine fraction and measuring the total activity concentration of radon progeny. The EEC of radon progeny was varied between 1.3 and 18.9 Bq m -3 with a mean value of 5.2 ± 0.48 Bq m -3. The mean activity thermodynamic diameter (AMTD) of ultrafine of radon progeny was determined to be 1.26 nm with relative mean geometric standard deviations (GSD) of 1.3. The ultrafine fraction of radon progeny, f b, has a range 0.01 to 0.21 with an average of 0.08 ± Based on the above experimental results, the deposition fractions have been evaluated in each air way generation through the human lung by applying a lung deposition model. The effect of radon progeny deposition by adult male has been also studied for various levels of physical exertion. The dose conversion factor has been discussed as a function of f b. Finally, the annual dose was calculated to be 0.36 msv. Keywords: radon progeny; equilibrium equivalent concentration; unattached activity size distributions of radon progeny; Deposition fractions; annual dose INTRODUCTION Over the past 50 y, there has been a considerable and increasing interest in natural radiation to which the people are exposed. The measurement of short-lived 222 Rn progeny ( 218 Po, 214 Pb, 214 Bi and 214 Po) in air has become a routine procedure for controlling the radiation exposure by inhalation. In general, the concentration of 222 Rn and its progeny in indoor air is on average 2 10 times higher than outdoor.[1-4]. This is due to low rates of air exchange and the dynamic collection into closed space, with additional contributions from 222 Rn sources such as building

2 66 A. Mohamed et al materials. The high concentrations of these radionuclides in indoor air coupled with the prolonged exposure periods related to indoor habitation make indoor 222 Rn decay products a potential health hazard. A large fraction of 218 Po (80-82%) is positively charged after their formation [5]. These atoms attach ambient water molecules or react with trace gases and H 2 o, No 2 and No vapors, grow by cluster formation, and become neutralized by the recombination with negative ions in the air and charge transfer processes (this is define as ultrafine or unattached fraction of radon progeny, they have a size range 0.5 to 5 nm [6-8]. These clusters attach to aerosol particles which suspended in the air and have a size range 1 nm up to 100 µm,[9], forming radioactive aerosol or attached fraction of radon progeny [10]. The basic processes of 222 Rn progeny behavior in the air are shown in Figure. 1. Figure 1. Basic processes of Rn progeny behaviour in air defining ultrafine and aerosol-attached activities The inhalation of radon progeny in the environment yields the greatest amount of natural radiation exposure of the human public. [11-14]. [15-17]. In all dosimetric models, the ultrafine and attached activities of radon progeny are among the most important parameters for estimating the radiation exposure. The ultrafine atoms may be deposited in the trachea and bronchial region, while the attached atoms are deposited in different parts of the pulmonary region due to different sizes of aerosol particles [18]. Epidemiological studies have established that enhanced levels of radon and its progeny in dwellings can cause health hazards and may lead to serious diseases, such as lung cancer [19, 20, 8]. Since it is difficult to measure the deposited activity in the respiratory system of the human being, the absorbed doses are calculated from models which need information about the equilibrium equivalent concentrations (EEC), ultrafine or unattached fraction, f b, and activity size distribution of ultrafine and attached radon progeny. Wire screens are commonly used to estimate ultrafine radon progeny in ambient and mine atmospheres. The use of wire screens for the separation of the ultrafine fraction was first studied by James et al., [21-23]. Measurements of activity size distribution of ultrafine and attached radon progeny show that the ultrafine fraction can well be separated from the aerosol particle attached activities [24-27]. The activity size distribution of radon progeny has been determined by tagging the natural aerosol particles with radon progeny. However, some measurements of radon progeny (for attached and ultrafine fraction) have been performed in indoor air [24], [28], [29-39], [8]. Most of the observed data of above literatures have shown that the size distribution consisted of ultrafine clusters with median diameters between 0.5 and 5 nm (unattached activity)

3 ACTIVITY OF ULTRAFINE FRACTION OF RADON PROGENY and progenies associated with ambient aerosol particles in sizes ranging between 100 and 500 nm (attached activity). The ultrafine fraction is deposited nearly completely in the respiratory tract during inhalation, whereas 80 percent of the attached are exhaled without deposition [40]. The amount of unattached activities up to about 10 percent of the total activity, but is considered to yield about 50 percent of the total radiation dose [40]. The decay products of 222 Rn in air are ordinarily not given by individual activity concentration, but rather by equilibrium equivalent concentration (EEC). The EEC is the total activity concentration (attached and ultrafine) of 222 Rn in radioactive equilibrium (equal activities) with its short lived progeny which has the same potential alpha energy concentration as the non-equilibrium mixture. The EEC of radon progeny is given by ICRP and UNSCEAR as [16], [41]. EEC = 0.105C C C (1) where C 1, C 2 and C 3 are the total activity concentrations (Bq/m 3 ) of 218 Po, 214 Pb and 214 Bi, respectively. For ultrafine equilibrium equivalent concentration, EEC un, is given by EEC un un1 un2 un3 = 0.105C C C (2) where C un1, C un2 and C un3 are the ultrafine activity concentrations (Bq/m 3 ) of 218 Po, 214 Pb and 214 Bi, respectively. The ultrafine fraction of radon progeny, f b, has much higher motilities in the air and can more effectively deposit in the respiratory system. Thus, for a long time the ultrafine fraction has been given extra importance in estimating health effects of radon progeny. The ultrafine fraction, f b, of radon progeny is given by: un EEC f b = (3) EEC Several observations have been carried out in indoor, and the value of f b in most cases was found to be varied from 0.03 to 0.4[10] [26], [29], [42-48], [33]. However, most of these measurements were performed in low ventilation rooms with additional aerosol sources such as cigarette smoke, cooking, burning candle, stove heating and air cleaner. Deposition theoretical modeling of radon containing aerosol in human lung represents a useful tool for interpret health effects from inhaled particular and for study the effectiveness of different inhalation procedure. Deposition is the process that determines what fraction of the inspired particles is caught in the respiratory tract and, thus, fails to exit with expired air. It is likely that all particles that touch a wet surface are deposited, thus, the site of contact is the site of initial deposition. Distinct physical mechanisms operate on inspired particles move them toward respiratory tract surfaces. Major mechanisms are inertial forces, gravitational sedimentation, Brownian diffusion, interception and electrostatic forces. A major factor governing the effectiveness of the deposition mechanisms is the parameters of the ultrafine and attached activity size distributions (active median thermodynamic diameter, AMTD, geometric standard deviation, GSD, and ultrafine fraction, f b ). Based on these parameters, the deposition fraction in each airway generation through the human lung has been calculated by using a lung deposition model. The present work summarizes the experimental data on EEC, EEC un and ultrafine fraction, f b, of radon progeny in different low-ventilated living room. Also, based on the obtained parameters of ultrafine and attached activity size distributions of radon progeny (AMTD, GSD),

4 68 A. Mohamed et al the deposition fractions in each airway generation of the human lung have been calculated by applying a lung deposition model [49]. In addition, the dose conversion factors as a function of ultrafine fractions have been discussed. Ultrafine Activity Size Distribution MATERIALS AND METHOD To measure unattached activity size distribution of short-lived radon progeny, a wire screen diffusion battery similar to that employed and calibrated by Cheng et al [53] was used. It was constructed with the same screen characteristics to determine the size distribution of ultrafine radon progeny. It consisted of five stainless-steel screens with 24, 35, 50, 200, and 635 mesh numbers. The screens were calibrated with monodisperse silver aerosol particles. The measured 50% cut-off diameters of the screens are 0.9, 1.3, 1.9, 4.0 and 7.9 nm. To determine the ultrafine activities of radon progeny, the aerosol attached and total radon progeny concentrations were measured. Each measurement consisted of two parallel samples: one with a single screen and the other as a reference sample without screen (this procedure was repeated with different screens, see Figure. 2). Figure 2. The screen diffusion battery, filter holder and surface barrier detector arrangement for the measurements of the unattached fractions of radon progeny. The screen was used only for collecting the ultrafine activities. The activities penetrating the screen (mostly attached to aerosol particle) and that of the reference sample were collected on membrane filters (Sartorius membrane filters type SM, 1.2 mm pore size, 25 mm diameter and an efficiency reaching about 100%) and the alpha activities were detected during and after air

5 sampling by a surface barrier detector. According to the Ruffle method [54] and through utilizing 241 Am as a radioactive source of alpha rays, the counting efficiency of the detector was found to be 17.0 ± 0.5%. The detector has an active area of 300 mm 2 and the separation between the filter and detector is 6 mm. With an energy resolution of about 300 kev, it was possible to distinguish the alpha particle energies emitted during the decay of 218 Po (6 MeV) and that of 214 Po (7.69 MeV). In order to determine the activity concentrations of radon progeny ( 218 Po, 214 Pb and 214 Bi), the measurements were performed in two steps. Firstly, the alpha particle spectrum was collected during a sampling period of 30 min. Secondly, after waiting for a time period of 30 min without sampling, the alpha particle spectrum was measured again (during decay) for a time period of 30 min. From the measured alpha counts of 218 Po and 214 Po during the sampling period and the 214 Po counts during the decay period, the activity concentrations of 218 Po, 214 Pb and 214 Bi could be calculated according to a method described by Wicke, [55]. The attached activities were derived from the sample obtained with the screen. The collected ultrafine activity on the screen is the difference between the measurements of the reference sample (without screen) and the screen sample The measurements of radon progeny concentrations were performed on different days. During the measurements the aerosol particle concentration was monitored by a condensation nuclei counter (General electric TSI, Model 3020). The counter can be used for determining aerosol particle concentration in the range from below 10 3 up to 10 7 cm 3. The parameters of ultrafine activity size distributions (AMTD and GSD) were obtained from the lognormal distribution method (William, 1999) as Σn i lndi ln( AMD) = Σn i 1 (4) 2 Σn (ln ln ) 2 i di AMD ln( GSD) = Σn i where n i, d i are the fraction and the cut-off diameter in the stage i, respectively. Also, these parameters can be obtained by a graphical cumulative method. The cumulative attached activities were plotted versus the cut-off diameter of the impactor stages. The AMTD is defined as the diameter at 50% cumulative fractions. The GSD of the size distribution is defined as the diameter at 84% cumulative activity divided by the diameter obtained at 50%. Deposition Calculation ACTIVITY OF ULTRAFINE FRACTION OF RADON PROGENY 69 Deposition of inhaled aerosols in any given region of the human respiratory tract depends upon particle size, shape, density and subject breathing pattern. In the present work, deposition calculations were based on the following set of aerosol characteristics pattern. Each component or mode of the radon progeny aerosol was assumed to be represented by a log normal distribution, in which the geometric standard deviation (GSD) is related to the activity median diameter (AMD) by NRC [56] GSD = [1 (100 AMD + 1)] (5) In the present investigation, the AMD of ultrafine fraction was 1.26 nm. Deposition fractions represent aerosol mass fraction deposited within specified regions during a complete breathing cycle normalized to the mass entering the trachea. A total lung volume 3000 cm 3, a tidal volume 1000 cm 3 and a spherical particles having a density equal 1g cm -3 were considered. Airway geometry was selected randomly and a deposition

6 70 A. Mohamed et al fraction in each airway generation of the human lung was calculated deterministically by using the deposition formulas which were described by Koblinker and Hofmann [49].. Ventilation rates were taken as 0.54 and 1.5 m 3 h -1 for rest and light exercise, respectively. These values have been substituted in the stochastic deposition model to calculate the amounts of radon progeny deposited in each airway generation, as function of aerosol size and breathing rate, for each subject x(1- f ) In radon dosimetry, dose conversion factor (DCF) is defined as the ratio between the weighted equivalent doses to EEC of radon progeny. DCF values may be obtained either based on results of epidemiologic studies or calculated applying dosimetric models [57]. Based on the obtained values of the f b, DCF have been calculated by using an empirical formula proposed by Porstendörfer [43]. DCF = 101xf + 6.7x(1- f ) for mouth breathing DCF m n = 23xf b b b b for nasal breathing The annual inhalation dose due to radon and its progeny is estimated according to the following formula [17], [58]. -6 DA ( msv) = T[ 0.17C + Rn 9EEC] x10 (7) where T is the time in hours a person spends at a particular location and C Rn is the concentration of radon gas in units of Bq m -3. The factors of 0.17 and 9 are the effective dose coefficients (nsv/bq h m -3 ) for radon and EEC, respectively. An average person spends time indoors with an occupancy factor of 0.8 averaged over 1 year [16], this gives T = 7008 h. In the present study, C Rn is estimated according to the following relation: EEC F (6) C Rn = (8) RESULTS AND DISCUSSIONS About forty samples have been carried out in different low ventilated room at Minia University, Minia city, Egypt. From the measured of activity concentrations, EEC, EEC un and f b of radon progeny have been calculated. The obtained values of EEC varied from 1.3 to 18.9 Bq m -3 with an average value of 5.2± 0.48 Bq m -3. Fig. 3 shows the frequency distributions of total equilibrium equivalent concentration, EEC. This distribution looks log-normal and has also been observed by many other authors during the measurements of radon progeny [58-63]. This log normal distribution indicates the dynamic behavior of radon progeny concentrations with either time or space. The parameters which responsible for temporal variations are temperature, moisture content, ventilation of the different parts of the building, 238 U concentration and radon exhalation rate from the soil and building materials [58]. The frequency distributions of ultrafine fraction, f b, are shown in Figure.4 where f b varied between 0.01 and 0.21 with a mean value of 0.08 ± The present mean value of f b (0. 08) is about three times higher than proposed in the literature, f b = 0.03, [64], [57], [41] [32] and lower than the mean value of 0.19 given by Kranrod et al [8]. The parameters of unattached activity size distributions and ultrafine fraction (EEC un ) of radon progeny as obtained from the measurements with diffusion battery are summarized in Table 1.

7 ACTIVITY OF ULTRAFINE FRACTION OF RADON PROGENY Frequancy EEC (Bq/m3 ) Figure 3. Frequency distribution of EEC 8 6 Frequancy Unattached fraction f b Figure 4. Frequency distribution of f b Table 1. The activity size distribution parameters of unattached EEC of short lived radon progeny Unattached parameters of EEC AMTD EEC un GSD (nm) (Bq m -3 ) ±0.08 ( ) ( ) ( )

8 72 A. Mohamed et al Fig. (5) presents the activity size distribution of ultrafine (EEC un ) fraction of radon progeny. The EEC of ultrafine fraction plotted vurses the cut-off diameter of the screen diffusion battary. the mean active median thermodynamic diameter (AMTD) of ultrafine fraction of EEC un is 1.26 nm ( ) with corresponding average geometric standard deviation of 1.3. The present AMTD (1.26 nm) is considered to be relatively higher than the values obtained (around 0.8 nm) by [33], [36], [67] Based on the obtained experimental parameters, the deposition fraction in each air way generation for adult male has been calculated by applying Mont Carlo deposition model of Koblinker and Hofmann [49]. Figure. 6 represents the deposition fraction that is predicted for each airway generation of the adult male lung over the size range of concern for deposition of radon progeny. This Figure relates the number of particles deposited in each airway generation to the number that enter the trachea on inhalation. It can be seen that the deposition fraction of particles with diameter of 1.26 nm are calculated to be uniformly high throughout the bronchi (generation 1 to 8). By the time the inspired air reaches the bronchioles (generation 9-15), the number of ultrafine airborne particles available for deposition was low. Therefore, deposition is found to be decrease rapidly in succeeding generations of the bronchiolar airways Relative EEC unattached fraction Cut off diameter(nm) Figure 5. Activity size distribution of ultrafine EEC in indoor air. The bronchial deposition fraction of particles in the size range of attached radon progeny were found to be about two orders of magnitude lower than those of unattached progeny. This clears that the disproportionately largely contributions to the dose from exposure to small fraction of radon progeny in the unattached state. The attached or so-called accumulation mode of the radon progeny aerosol has a median size in ambient air that ranges from about 150 to 400 nm diameter [68], [36]. However, the carrier aerosol particles are considered to be partially hygroscope and grow in the respiratory tract to about double their ambient size. Another significant factor that must be accounted for the calculating of deposition profile of radon progeny within the respiratory tract is the typical variability or dispersion in size of the aerosol particles. Ultrafine radon progeny have a relatively narrow distribution of particle size,

9 ACTIVITY OF ULTRAFINE FRACTION OF RADON PROGENY 73 whereas the activity-size distribution of progeny attached to ambient aerosol particles is typically broad AMD=1.25 AMD=350 Deposition fraction Generation number Figure 6. Deposition fraction calculated with varying particle diameters. Deposited fraction rest 1.26 light 350 light 350 rest Airway generation number Figure 7. Effect of exercise on fraction of particles deposited in each airway generation at two levels of physical activity for an adulate male (resting, 0.54 m 3 h -1 and light work, 1.5 m 3 h -1 ). Figure. 7 illustrates how the deposition profiles of ultrafine and attached progeny are expected to be influenced by subject s breathing rate. An increase in the breathing rate (from rest to light work) is found to decrease the deposition fraction with which inhaled progeny were deposited in the bronchi. As the ventilation rate increased from 0.54 to 1.5 m 3 h -1, the average deposition fraction of airway generations 1 through 8 were expected to decrease by 22 % for 1.26 nm particles and by about 38 % for 350 nm particles. Based on the obtained f b, the DCF has been evaluated [69], [48] by applying lung models [43]. The calculated DCF (for mouth and nasal) are plotted versus f b as in Figre. 8. It is clear from

10 74 A. Mohamed et al this figure that the DCF is affected where the inhalation is through the nasal or mouth Mouth Nosel DCF (msv/wlm) Unattached fraction Figure 8. DCF as a function of unattached fraction Due to equation 7 (EEC= 5.21 Bq m -3 and equilibrium factor F = 0.4), the annual dose was calculated to be 0.36 msv. CONCLUSIONS The following conclusions can be drawn from the results of the present work: 1. A significant factor that must be accounted for calculating the deposition profile of radon progeny within the respiratory tract is the typical variability or dispersion in size of the aerosol particles. Unattached radon progeny have a relatively narrow distribution of particle size, whereas the activity size distribution of progeny attached to ambient aerosol particles is typically broad. 2. The obtained parameters of the activity size distribution (AMTD and GSD) are necessary to calculate the deposition and dose in the human lungs. For best estimation of doses, accurate data on these parameters are necessary. Simultaneous measurements of short lived radon progeny in different environments (indoor, outdoor, mine) are necessary in order to model the timedependent behavior, deposition and attachment and to determine the particle size distribution. REFERENCES [1] K.N. Yu, T. Cheung, Z.J. Guan, E.C.M. Young, B.W.N. Mui, Y.Y. Wong, Concentration of 222Rn, 220Rn and their progeny in residences in Hong Kong, Environmental Radioactivity , (1999). [2] M.H. Magalhaes, E.C.S. Amaral, I. Sachett, E.R.R. Rochedo, Radon-222 in Brazil: An outline of indoor and outdoor measurements, Environmental Radioactivity , (2003). [3] T. Anastasiou, H. Tsertos, S. Christofides, G. Christodoulides, Indoor radon ( 222 Rn) concentration measurements in Cyprus using high-sensitivity portable detectors, Environmental Radioactivity , (2003).

11 ACTIVITY OF ULTRAFINE FRACTION OF RADON PROGENY 75 [4] H. Papaefthymiou, A. Mavroudis, P. Kritidis, Indoor radon levels and influencing factors in houses of Patras, Greece, Environmental Radioactivity , (2003). [5] J. Porstendörfer, T.T. Mercer, Influence of electric charge and humidity upon diffusion coefficient of radon decay products, Health Physics , (1979). [6] M. Ramamurthi, P.K. Hopke, On improving the validity of wire screen unattached fraction Rn daughter measurements, Health Physics , (1989). [7] R.S. Květoslav, Aerosol Chemical Processes in the Environment, Boca Raton, FL: Lewis Publishers, p. 600, (2000). [8] C. Kranrod, S. Tokonami, T. Ishikawa, A. Sorimachi, M Janik, R. Shingaki,et al., Mitigation of the effective dose of radon decay products through the use of an air cleaner in a dwelling in Okinawa, Japan, Applied Radiation and Isotopes , (2009). [9] W. Nazaroff, V. Nero, Radon and Its Decay Products in Indoor Air, Wiley, New York, p. 44, (1988). [10] J. Porstendörfer, Properties and behavior of radon and thoron and their decay products in the air, Aerosol Science , (1994). [11] B. Altshuler, N. Nelson, M. Kuschner, Estimation of lung dose from the inhalation of radon and daughters, Health Physics , (1964). [12] W. Jacobi, The dose to the human respiratorytract by inhalation of short-lived 222 Rn and 220 Rn decayproducts, Health Physics , (1964). [13] E. Pohl, J. Pohl-Ruling, Dose calculations due to the inhalation 222 Rn, 220 Rn and their daughters, Health Physics , (1977). [14] J.A. Auxier, Respiratoryexposure in buildings due to radon progeny, Health Physics , (1976). [15] A. Toth, Determining the respiratorydosage from RaA, RaB and RaC inhaled bythe population in Hungary, Health Physics , (1972). [16] United Nations Scientific Committee on the Effects of Atomic Radiation. (UNSCEAR), Sources, effects and risks of ionizing radiation. Report to the General Assembly, with annexes. United Nations Publications, New York, (1993). [17] United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), sources and effects of ionizing radiations. Report to the General Assembly with Scientific Annexes. United Nations, New York, (2000). [18] M. Shimo, T. Torri, Y. Ikebe, Measurements of unattached and attached RaA atoms in the atmosphere and their deposition in human respiratory tract, Atomic Energy Society of Japan , (1981). [19] F. Bochicchio, F. Forastiere, D. Abeni, E. Rapiti, Epidemiologic studies on lung cancer and residential exposure to radon in Italy and other countries, Radiation Protection Dosimetry 78 (1) 33, (1998). [20] R.W. Field, D.J. Steck, B.J. Smith, C.P. Brus, J.S., Neuberger, E.F. Fisher, et al., Residential gas exposure and lung cancer: the low radon lung cancer study, Am. J. Epidemiol. 151 (11) 101, (2000). [21] A.C. James, G.F. Bradford, D.M. Howell, Collection of unattached RaA atoms using wire gauge, Aerosol Science 3 243, (1972). [22] J.W. Tomas, L.E. Hinchliffe, Filtration of mm particles with wire screens, Aerosol Science 3 387, (1972). [23] A.C. George, Measurement of uncombined fraction of radon daughters with wire screens, Health Phys , (1972). [24] A. Reineking, K.H. Becker, J. Porstendorfer, Measurements of the activity size distributions of the short lived radon daughters in the indoor and outdoor environment, Radiation Protection Dosimetry , (1988). [25] K.W. Tu, E.O. Knutson, Indoor radon progeny particle size distribution measurements made with two different methods, Radiation Protection Dosimetry , (1988).

12 76 A. Mohamed et al [26] A. Reineking, J. Porstendörfer, Unattached fraction of short-lived Rn decay products in indoor and outdoor environments: An improved single-screen method and results, Health Physics , (1990). [27] A.C. George, E.O. Knutson, Particle size of unattached radon progeny in filtered room air, Radiation Protection Dosimetry , (1994). [28] A. Reineking, E.A. Knutson, A.C. George, S.B. Solomon, J. Kesten, G. Butterweck, et al., Size Distribution of unattached and aerosol-attached short-lived radon decay products: Some results of intercomparison measurements, Radiation Protection Dosimetry , (1994). [29] A. Reineking, J. Porstendörfer, V. Dankelmann, J. Wendt, The size distribution of the unattached short-lived radon decay products, Radioaktivität in Mensch und Umwelt, Band I, , Publication Series: Radiation Protection p (in German) (1998). [30] P.K. Hopke, M. Ramamurthi, C.S. Li, Measurement of the size distributions of radon progeny in indoor air, In Aerosol: Science, Industry, Health and Environment, S. Masuda, K. Takashi, (eds.), 2, Pergamon Press, Ltd, Oxford, pp , (1990). [31] P.K. Hopke, P. Wasiolek, N. Montassier, A. Govallo, K. Gadsby, R. Socolow, Measurement of activity-weighted size distributions of radon decay products in a normally occupied home, Radiation Protection Dosimetry , (1992). [32] C. Huet, G. Tymen, A. Reineking, J. Wendt, Inter-comparison measurements of the activity size distribution of aerosol attached short-lived radon decay products in a dwelling located in Brittany, Aerosol Science , (1998). [33] C. Huet, G. Tymen, D. Boulaud, Size distribution, equilibrium ratio and unattached fraction of radon decay products under typical indoor domestic conditions, The Science of the Total Environment , (2001). [34] Y.S. Cheng, T.R. Chen, H.C. Yeh, J. Bigu, R. Holub, K. Tu, et al., Intercomparison of activity size distribution of thoron progeny and a mixture of radon and thoron progeny, Environmental Radioactivity 51 59, (2000). [35] K. Fukutsu, Y. Yamada, S. Tokonami, T. Iida, A new graded screen array for radon progeny size measurements and its numerical verification, Atmospheric Electricity 23 49, (2003). [36] M. Georges, Risk assessment of exposure to radon decay products, final report, Commission of the European Communities C.E.C, (2000). [37] K. Yamasaki, Y. Oki, Y. Yamada, S. Tokonami, T. Iida, Optimization of measuring methods on size distribution of naturally occurring radioactive aerosols, International Congress Series , (2005). [38] S. Tokonami, K. Fukutsu, Y. Yamada, Y. Yatabe, Particle size measurement of radon decay products using MOUDI and GSA, International Congress Series , (2005). [39] R. Mishra, Y.S. Mayya, H.S. Kushwaha, Measurement of 220Rn/222Rn progeny deposition velocities on surfaces and their comparison with theoretical models, Aerosol Science 40 1, (2009). [40] A.C. James, F.T. Cross, J.S. Durham, J.K. Briant, P. Gehr, R. Masse, et al., Dosimetry model for bronchial and extrathoracic tissues of the respiratory tract, Radiation Protection Dosimetry , (1991). [41] International Commission on Radiological Protection, Lung Cancer Risk from Indoor Exposure to Radon Daughters. Pergamon Press, Oxford ICRP Publication, p.50, (1987) [42] J. Porstendörfer, A. Reineking, Indoor behaviour and characteristics of radon progeny, Radiation Protection Dosimetry , (1992). [43] J. Porstendörfer, Radon: measurements related to dose, Environment International 22, (1996). [44] J. Porstendörfer, Physical parameters and dose factors of the radon and thoron decay products, Radiation Protection Dosimetry 94 (4) 365, (2001).

13 ACTIVITY OF ULTRAFINE FRACTION OF RADON PROGENY 77 [45] T.W. Piotr, C.J. Anthony, Unattached fraction measuring technique and radon lung dose, Journal of Environmental Radioactivity 51(1) 137, (2000). [46] K.N. Yu, E.C.M. Young, K.C. Li, A study of factors affecting indoor radon properties, Health Physics 71 (2) 179, (1996). [47] J. Vaupotič, Nano-size radon short-lived progeny aerosols in slovenian kindergartens in winter time, Chemosphere , (2007). [48] J. Vaupotič, Nanosize radon short-lived decay products in the air of the Postojna Cave, Science of the Total Environment , (2008). [49] L. Koblinker, W. Hofmann, Monte carlo model for aerosol deposition in human lungsp: Part 1. Simulation of Particle Transport in A stochastic Lung Structure, Aerosole Science , (1990). [50] C. Lurzer, On the determination of multimodal size distributions of atmospheric aerosols, cascade impactors agent under pressure, Dissertation, Wien, Austria (1980). [51] A. Reineking, H.G. Scheibel, A. Hussin, K.H. Becker, J. Porstendorfer, Measurements of stage efficiency functions including inter-stage losses for sierra and berner impactor and evaluation of data by modified simplex method, Aerosol Science , (1984). [52] W.C. Hinds, Aerosol Technology, Properties, Behavior, and Measurement of Airborne Particles, 2nd ed., Wiley, New York, (1999). [53] Y.S. Cheng, Y.F. Su, G.J. Newten, H.C. Yeh, Use of a graded diffusion battery in measuring the activity size distributions of thoron progeny, Aerosol Science , (1992). [54] M.P. Ruffle, The geometrical efficiency of a parallel disc-source and detector system, Nuclear Instruments and Methods , (1967). [55] A. Wicke, Studies on the question of the natural radioactivity of the air in living spaces and stay. Ph.D. Thesis, University Giessen, Germany (1979). [56] National Research Council (NRC), Comparative Dosimetry of Radon in Mines and Homes, National Academy Press, Washington, (1991). [57] International Commission on Radiological Protection, Protection Against Radon-222 at Home and at Work. Pergamon Press, Oxford ICRP Publication, p. 65, (1994). [58] M. Singh, K. Singh, S. Singh, Z. Papp, Variation of indoor radon progeny concentration and its role in dose assessment, Environmental Radioactivity , (2008). [59] A.M. Marenny, A.S. Vorozhtsov, N.A. Nefedov, O.A. Orlova, Results of radon concentration measurements in some regions of Russia, Radiation Measurements 26 43, (1996). [60] C. Duenäs, M.C. Fernandez, J. Carretero, E. Liger, Natural radioactive levels in atmospheric air in M_alaga (Spain), Applied Radiation and Isotopes , (1996). [61] M.I. Al-Jarallah, F. Rehman, F. Abu-Jarad, A. Al-Shukri, Indoor radon measurements in dwellings of four Saudi Arabian cities, Radiation Measurements , (2003). [62] K.M. Abumurad, M.H. Al-Tamimi, Natural radioactivity due to radon in Soum region, Jordan Radiation Measurements 39 77, (2005). [63] C. Diyun, Y. Xingbao, H. Ruiying, Indoor radon survey in indoor environments in Zhuhai City, China, Radiation Measurements , (2005). [64] Nuclear Energy Agency (NEA), Dosimetry aspects of exposures to radon and thoron daughter products report by a group of experts of the OECD, NEA, September, (1983). [65] L.S. Ruzer, N.H. Harley, Aerosol Handbook, Measurement, Dosimetry and Health Effects, CRC Press, New York, p. 709, (2005). [66] A.A. Ahmed, Studies of aerosol deposition on surfaces. Ph.D. Thesis, University Giessen, Germany, (1979). [67] J. Porstendörfer, A. Reineking, Radon characteristics in air and dose conversion factor, Health Physics 76 (3) 300, (1999).

14 78 A. Mohamed et al [68] G. Butterweck-Dempewolf, C. Shuler, G. Vezzu, Size distribution of the unattached fraction of radon progeny, European Conference on Protection against Radon at Home and at Work, Praha, Czech Republic, June 2-6 (1997). [69] H. Fakir, W. Hofmann, R.S. Caswell, I. Aubineau-Laniece, Microdosimetry of inhomogeneous radon progeny distributions in bronchial airways, Radiation Protection Dosimetry,, p. 113, (2005). اط ا ا ا اادون ا#اء دا! اف ع. *() م.,+ م. ) ا#دى و /.- اء آ ام ا ا&%ق #ا"! ا دون- ٢٢٢ 23 ا 01 آ/. -ن ا, +* ا(#ن. و+* ا/ 6 ا "5 #ا"! ا ادون +* ا 8 ء ا=آ/ > ا& ض ا(: 9 * 58 ر. ا%ط ا(: 9 * +,A ا 5@? اا"! <ا* ١٠% > ا%ط ا(: 9 * ا F * (ا& AH و+, A ا) إL أ# J &! <ا* ٥٠% > ا 8 9 ا(: 9 ا F. + Qن R@S ت ا/ +,O ا ه TO& ا 8 9 ا(: 9. و" 2 * ا Tرا ا 0 ا/#ت ا O & آات +,O ا ) ) b (EEC un ا/ +,O ا f) و"زت آات ا("ان ا 6+F " (EEC) ا("ان ا 6+F ا F ا 80 %ط ا(: 9 * W ا& AH ا"! ا ادون +* W + W Tة ا& 5 +* ا T ا H. ا&\T] 2Sر إ#&%ر <8/ &Z8 ا 8 ء +,A ا وس " آات ا%ط ا(: 9 * ا F * ا"! ا ادون. ٣ ٣ TT0" ". &/ FS ٠,٤٨ ± ٥,٢ 2& " او<] EEC) ( ا"! ا ادون <S ١,٣ و ١٨,٩ OS &/ FS ا 0# اف S&e ##& ١,٢٦ Fن ا +,O ا ادون ا"! (AMTD) ارى ا 0 ا FT * ا 2O &e رى ه T * #/* (GSD) ١,٣. ا/ +,O ا ا"! ا ادون ) b f) آ#] ذات Tى ٠,٠١ إ* S&e ٠,٢١ *+ ر, ا(#ن *+ آ < رات / ± ٠,٠٨.٠,٠٣ وا 9 &دا *9 ا&,! ا& 8 / ه@? " TO" ا. ا& /ت #ا"! ا ادون +* ر, L0 ت js \& > " kl" ا 5 اء S &\ Tام #ذج ". +* ا,. " أ m درا ا( 5 دات ا/ T #. آ " % "0 ا 8 9 آTا +* ) b f). و+* ا 5 " <ب ا 8 9 ا & Fن * ٠,٣٦ ت.