Free fraction radon daughters

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). 

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]

The mean value of the equilibrium factor F measured in houses without aerosol sources was 0.3 t 0.1 and increased up to 0.3 by additional aerosol particles in the room air. The fraction of the free radon daughters had values between fp = 0.06-0.13 with a mean value near 0.1. Only additional aerosol sources led to a decrease of f - values below 0.05. 

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. ... 

Each serie of measurements consisted of two parallel samples with counting during and after sampling, one with the screen diffusion battery and the second as the reference sample, so that the fractional free radon daughters could be calculated. The radon daughters are collected on a membrane filter (filter diameter 25 mm, pore diameter 1.2 ym) and the decays of Po-218 and Po-214 are counted by means of alpha spectrometry with a surface barrier detector (area 300 mn ). 

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 results of these measurements show that the fraction of the free radon daughters in rooms with low and moderate ventilation and without any aerosol sources are higher (fp = 0.06 - 0.15) than proposed in literature (Jacobi and Eisfeld, 1980 ICRP 32, 1981 NEA, 1983). A mean value of 10 % (fp = 0.1) was determined. Only additional aerosol sources in a room such as cigarette smoke, cooking, candle light or stove heating led to a decrease of the fp-value below 0.05. 

Radon daughters are deposited on the surface of mucus lining the bronchi. It is generally assumed that the daughter nuclides, i.e. polonium-218 (RaA), lead-214 (RaB) and bismuth-214 (RaC), remain in the mucus and are transported towards the head. However, one dosimetric model assumes that unattached radon daughters are rapidly absorbed into the blood (Jacobi and Eisfeld, 1980). This has the effect of reducing dose by about a factor of two. Experiments in which lead-212 was instilled as free ions onto nasal epithelium in rats have shown that only a minor fraction is absorbed rapidly into the blood (Greenhalgh et al., 1982). Most of the lead remained in the mucus but about 30% was not cleared in mucus and probably transferred to the epithelium. 

Porstendorfer, J., Reineking, A. Becker, K.H. (1987) Free fractions, attachment rates and plate-out rates of radon daughters in houses. In Radon and its Decay Products, ed. P.K. Hopke, Washington D.C., American Chemical Society, pp. 285-300. 

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