Attachment, rate

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. 

This paper deals with the plate-out characteristics of a variety of materials such as metals, plastics, fabrics and powders to the decay products of radon and thoron under laboratory-controlled conditions. In a previous paper, the author reported on measurements on the attachment rate and deposition velocity of radon and thoron decay products (Bigu, 1985). In these experiments, stainless steel discs and filter paper were used. At the time, the assumption was made that the surface a-activity measured was independent of the chemical and physical nature, and conditions, of the surface on which the products were deposited. The present work was partly aimed at verifying this assumption. 

The underlying physical and/or chemical mechanisms responsible for the differences observed between the radon progeny and the thoron progeny as related to different materials are not clearly understood. Finally, it should be pointed out that the main thrust in this paper was to determine differences in surface a-activity measured on different materials with the same geometrical characteristics exposed to identical radioactive atmospheres. The calculation of deposition velocities and attachment rates, although it follows from surface a-activity measurements, was not the intent of this paper. This topic is dealt with elsewhere (Bigu, 1985). 

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 attachment rate to the atmospheric aerosol X=0 Z, is a linear function of the particle concentration Z. Values of 5 10 3 cm3h-l for the average attachment coefficient B measured in laboratory rooms were reported by Mohnen (1969) and Porstendorfer and Mercer (1978). 

This paper will summerize our experimental data on the equilibrium factor (F), the free fraction (f ), the attachment rate to the room air aerosol (X), the recoil factor r and the plateout... 

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). 

In Fig. 3 all measured data of fj = cjf/cj and f are presented as function of the attachment rate. The absolute errors of fj and fp are in the order of 0.02 and 0.01, respectively. These errors were calculated from the errors due to the alpha counting and due to the mathematical procedure of the filter activity evaluation. 

Figure 3. Ratios of the free to the total activity concentrations of RaA and RaB and fp as function of the attachment rate X measured in eight rooms of different houses.

Porstendorfer, J. and T.T. Mercer, Influence of Nuclei Concentration and Humidity upon the Attachment Rate of Atoms in the Atmosphere, Atmospheric Environment 12 2223-2228 (1978). 

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...

The complete description of the model is beyond the scope of the paper. In Figure 5 it is shown that at low attachment rates the deposition rate of the unattached daughters ( un) can be evaluated and at high attachment rates the ventilation rate. 

On this basis the ventilation rate was fitted to the data at high attachment rates and compared to the measured ventilation rate so that the ratio of the "outroom" to the "inroom" daughter concentration (P) could be calculated (Table III). Afterwards the deposition rate of the unattached daughters was calculated from the... 

In Figure 9 it is shown that the attachment rate is the dominating factor for the unattached fraction. The equilibrium factor however, is also strongly influenced by the deposition rate of the unattached daughters. The curves are calculated as in Figure 7. The limited fluctuations of the actual data illustrate the importance of the attachment rate. 

Figure 7. Effective dose equivalent per hour and per unit radon concentration (AJ-B, 7 J-E) as a function of the equilibrium factor. The full lines are calculated with the mean values of the 72 measurements (Xa -. 37/h, XVent . 41/h, P -. 53, A.M.D. —. 15 lJm) and changing attachment rates.

Figure 9. Effective dose equivalent per hour and per unit radon concentration (A J-B, V J-E), equilibrium factor ( ) and unattached fraction (o, right ordinate) versus the attachment rate. The curves are calculated as in Figure 7.

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. 

Porstendorfer, J. and T. Mercer, Diffusion Coefficient of Radon Decay Products and their Attachment Rate to the Atmosphere Aerosol, in Natural Radiation Environment III. (T. F. Gesell and W. M. Lowder, eds.), CONF-780422, Vol. 1, pp. 281-293, National Technical Information Service, Springfield, Virginia (1980). 

The quantity k3 may be considered as an instrumental constant to be determined in a blank experiment—that is, without added solute. In this case, the current is given by I(t)/I(0) = (1 - vt/d) exp( - k3 t), from which k can be determined. With the solute added, the current initially decays exponentially (fast decay) from which is determined h + k2 + k3, while the ratio of the initial plateau to the initial current gives k2/(k] + k2 + k ). The detachment rate k2 is now obtained from the last two numbers, and then the attachment rate fe, is also obtained since k3 is already predetermined. In short, both attachment (kj and detachment (k2) rates are obtainable from the time dependence of the cell current following a brief pulse of ionizing radiation. 

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