Deposition velocity daughters

Scott, A.G., Radon Daughter Deposition Velocities Estimated from Field Measurements, Health Physics 45 481-485 (1983). 

Bigu, J., Radon Daughter and Thoron Daughter Deposition Velocity and Unattached Fraction Under Laboratory-Controlled Conditions and in Underground Uranium Mines, Aerosol Sci., 16 157-165 (1985). 

Porstendorfer, 1984). Knutson et al. (1983) measured similar results in their chamber investigation. The results show that the values of the deposition velocity of the free radon daughters are about 100 times those of the aerosol radon progeny. But there are no information about the effective deposition surface S of a furnished room for the calculation of the plateout rates qf and qa by means of Vg and Vg. For this reason the direct measurements of the plateout rates in rooms are necessary. Only Israeli (1983) determined the plateout rates in houses with values between qf = 3-12 h"1 and qa = 0.4-2.0 h"1, which give only a low value of the... 

The deposition velocities of the unattached daughters were calculated from the measurements in the radon chamber with the bare filter (Figure 2) and found to equal. 095+.007 cm/s for Po-218,. 085+.012 cm/s for Pb-214 and. 045+.015 cm/s for Bi-214. This decrease in deposition velocity is one of the most important sources of error in the room model. 

The deposition rate and the corresponding deposition velocity of the unattached daughters is found to have a value of 18/h and. 19 cm/s in the rooms and 8/h and. 08 cm/s in the cellar. The latter could be corrected to. 12 cm/s applying the same decrease in deposition velocity to the attached daughters as was found for the unattached daughters. The remaining difference is probably due to a smaller air velocity in the cellar and to a difference in roughness of the surface (concrete instead of wall paper and carpets). 

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

The dry deposition velocity of lead-212, a thoron (thoron or radon-220 itself originating from thorium-232) decay product has been reported to be in the range 0.03-0.6 cm/sec (Bigu 1985 Rangarajan et al. 1986). These low deposition velocities indicate that the thoron daughter, stable lead, may have a long residence time in the atmosphere with respect to dry deposition. 

Bigu J. 1985. Radon daughter and thoron daughter deposition velocity and unattached fraction under laboratory-controlled conditions and in underground uranium mines. J Aerosol Sci 16 157-165. 

Samuelsson (1984) reintroduced wire screens as a means of measuring the amount of unattached 21 Po. He assumed 0.05 cin /sec for the diffusion coefficient, then applied the Cheng-Yeh equation to calculate the amount caught on the screen. An experiment like that of James et al (1972) was done to determine a-activity countable from the front face of the screen. For a 200 mesh screen at face velocity comparable to our face velocities, Samuelsson found this amount to be 80% of that for the same amount of material deposited on a filter. This agreed with the James et al (1972) result for comparable face velocity. In conclusion, it is clear that no size spectra could be measured by the above techniques for unattached daughters and that a better technique must be developed. 

FIGURE 7-6 Transfer-coefficient contours during inhalation for 0.088-Mm-diameter particle.deposition in the daughter branch of the three-dimensional bifurcation model shown in Figure 7-1. The time-averaged velocity in the parent branch, U, is 100 cm/sec. Total surface area 18.6 cm X distance (in centimeters) downstream from the Carina Y - deposition locations around the branch circumference with F - 0 at the Carina. Each unit of the ordidnate corresponds to a distance of 0.215 cm. Adapted from Bell. ... 

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