Radon daughters attachment

Exposure. Inhalation (radon daughters attach to lung tissue and decay, resulting in the deposition of radiation, in the form of alpha particles, in the lung tissue) ingestion of radon-containing groundwater. 

Palmer H, Perkins R, Stuart B. 1964. The distribution and deposition of radon daughters attached to dust particles in the respiratory system of humans exposed to uranium mine atmospheres. Health Phys 10 1129-1135. 

Unattached Fraction—That fraction of the radon daughters, usually 218Po and 214Po, which has not yet attached to a dust particle or to water vapor. As a free atom, it has a high probability of being exhaled and not retained within the lung. It is the attached fraction which is primarily retained. 

Porstendorfer, J., A. Reineking, and K.H. Becker, Free Fractions, Attachment Rates and Plateout Rates of Radon Daughters in Houses, this volume (1987). 

From equation (3) is is clear that the kinetic theory predicts an attachment rate of radon daughters to aerosol particles proportional to the square of the diameter of the aerosol particle. 

McLaughlin, J.P., The Attachment of Radon Daughters to Condensation Nuclei, Proc. Royal Irish Academy 72, Sect. A., 51 (1972). 

The general characteristics of these ions have been reviewed by Bricard and Pradel (1966). The attachment of radon and thoron daughter ions to aerosols including condensation nuclei has been studied by a number of investigators (Raabe, 1968 McLaughlin, 1972 Porstendorfer and Mercer, 1979 and Busigin, et al., 1981), and will not be considered further in this paper. We turn now to some experimental results that bear directly on the characteristics of the radon daughter ions. 

The most significant information given in Table I is that the radon daughter ions do contribute to the total internal dose if only at about 3% in this study. The effect of free ions in contrast with daughters attached to aerosols is substantial when the mechanics of deposition in the bronchial tree and lungs are taken into account. The dose from "unattached" Po-218, which includes the Po-218 positive ions as a major component, can be from 3 to 40 times that of the attached Po-218 (NCRP, 1984). Current dosimetry models allow for the important role played by Po-218 in small-ion form. Hence, their effect is significantly greater than the 3% contribution to the PAEC (WL) shown in Table I. 

Free Fractions, Attachment Rates, and Plate-Out Rates of Radon Daughters in Houses... 

The paper summerizes the experimental data on the equilibrium factor, F, the free fraction, fp, the attachment rate to the room air aerosol, X, the recoil factor,, and the plateout rates of the free, qf, and the attached, q3, radon daughters, determined in eight rooms of different houses. In each room several measurements were carried out at different times, with different aerosol sources (cigarette smoke, stove heating etc.) and under low (v<0.3 It1) and moderate (0.3[Pg.288]

Besides the attachment rate the plateout rates had the greatest influence on F and fp. The plateout rates of the free, qf, and the attached, qa, radon daughters obtained in rooms with low ventilation varied between 20 and 100 hr1 and 0.1 and 0.4 h 1 with average values of about 40 hr1 and 0.2 h 1,... 

The activity concentration of radon and of the free and aerosol attached radon daughters i/ere measured simultaneously. During these measurements the aerosol particle concentration i/as registered by means of a condensation nuclei counter (General Electric). 

For the determination of the free fraction the attached and the total radon daughter activity concentration were measured. The separation of the free radon daughters from the total daughter concentration was carried out by means of a high-volume diffusion screen battery (Reineking and Porstendorfer, 1986) with a 50 % penetration efficiency for 4 nm particles and for a flowrate of 2.4 m h-1. ... 

For the determination of the radon daughter concentrations down to 1 Bq m 3 a counting and sampling time of 60 minutes and a counting time of 20-40 minutes after the end of sampling were used. From the counts of Po-218 and Po-214 of the two samples measured in different intervals the concentrations of the free and attached radon daughters were calculated (Wicke and Porstendorfer, 1983). 

All our measurements i/ere carried out in rooms with i < 1 hr1 and the radon concentration outdoors (c 5 Bq nr 3) i/as always much smaller than indoors (cj > 100 Bq m 3). Assuming a constant radon emanation, a homogeneous activity distribution and 100 % prefiltering of the free fractions of the incoming air, the radon, the free and attached radon daughter activity concentrations indoors (cj cjf cja) and outdoors (eg c f c a) under steady conditions are ... 

The concentrations of radon (cj) and the free (c f, c2f ) and on aerosol attached (cja, cja, cja radon daughters vi/ere measured and with these data the equilibrium factor F and the free fraction of the radon daughters fp were calculated. The room parameters (e, v) and the parameters of radon daughter transport processes (X, qf, q3, ri) were evaluated by means of equations (3), (4), (8), (9), (10) and (11) using the measured data. 

The free fraction of the radon daughters f measured in rooms with lo i/ ventilation and no aerosol sources shows values between 0.06 - 0.15 (Table lb) with a mean value near 0.10. In this case the values of the attachment rates X range between 20 hr and 40 hr. The fp-values < 0.05 were obtained in rooms with aerosol sources, which always had values of the attachment rate > 100 It1 (Table III). 

The same kind of optimization has been performed for the thoron daughters. In the calculations the sampling period was set at 30 min and the first decay time interval is started after the decay of the radon daughters (270 min). For a total measurement time of 16 hours the optimized MMC of Pb-212 and Bi-212 are respectively 0.02 Bq/m and 60 Bq/m (270-370 min, 540-960 min). Better results for Bi-212 are obtained with only one decay time interval and an estimation of the ratio of Pb-212 to Bi-212 out of the removal processes (ventilation and deposition of the attached thoron daughters). The influence of the removal rate on the potential alpha energy concentration is small. For the decay interval (270-960 min) the MMC of Pb-212 is 0.014 Bq/m, assuming the sum of the removal rates to be 0.6+0.5/h. 

Figure 3. Evolution of the attachment rate, the deposition rate of the attached daughters, the ventilation rate and the radon daughter concentrations ( A Po-218 Pb-214 Bi-214...

Table V. Summary of the deposition velocities of the attached and unattached radon daughters and the corresponding deposition rates from various researchers.

Vanmarcke, H., Janssens, A. and Raes, F., The equilibrium of attached and unattached radon daughters in the domestic environment, The Science of the Total Env. 45 251 (1985)... 

Figure 4a shows the results for CN levels at 70 cm 3 and below. As pointed out earlier (Holub, 1984), there are no attached radon daughters because the attachment rate is negligible compared to 218Po half life. There is no observable growth and the clusters are very close to the oxide of 218Po. All sets agree reasonably well. Error bars are from repeated measurements. 

Busigin, A., A.W. van der Vooren, and C.R. Phillips, Attached and Unattached Daughters Measurements and Measurement Techniques in Uranium Mines, in Proceedings of the Bureau of Mines Conf. on Radon Daughter Plateout Phenomena, (P.K. Hopke, ed.) pp. 99-101, Univ. of Illinois, Urbana, IL, April 16-18 (1980). 

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