High {sup 222}Rn levels, enhanced surface deposition, increased diffusion coefficient, humidity, and air change effects
- International Academy of Hi-Tech Services, Inc., Cleveland, OH (United States)
Measurements have been made of surface deposition rates for {sup 218}Po radon decay products in a small (0.283 m{sup 3}) aluminum test chamber for {sup 222}Rn levels from 1 to 1,600 kBq m{sup -3}. An increase in macroscopic surface deposition rate has been found to be induced by the high {sup 222}Rn concentrations. A distinct {sup 222}Rn level threshold has been found below which plateout is constant at the normal rate for ambient residential conditions. Above the threshold, an increase in plateout is observed and the transition quickly reaches a constant, higher plateout rate. With all environmental conditions remaining constant and varying humidity, the threshold {sup 222}Rn level decreases with increasing relative humidity. The rate of rise to the new plateau is found to increase with increasing humidity. For the constant air change rate of ACH = 0.2 h{sup -1}, the fraction of airborne {sup 218}Po lost by the enhanced plateout was consistently 0.4{plus_minus}0.25 for seven values of humidity from 8 to 54% RH. For a fixed RH = 40{plus_minus}2%, it was found that the threshold increases from 5 to 58 kBq m{sup -3} for a change in ACH from 0 to 1.06 h{sup -1}. In converting the deposition data to values of diffusion coefficient, D, using Crump and Seinfeld`s theory, a very high D of 0.18 cm{sup 2} s{sup -1} for high {sup 220}Rn levels is obtained if D = 0.07 cm{sup 2} s{sup -1} is assumed for ambient air conditions. Results indicate an ambient D = 0.027 cm{sup 2} s{sup -1}. The results may impact on research utilizing high levels in test chambers and diffusion tubes to measure radon progeny properties such as diffusion coefficients and attached and unattached fractions, and also for cancer studies using animals with {sup 222}Rn levels as much as 10{sup 4} times than ambient residential levels. 36 refs., 10 figs., 5 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 369936
- Journal Information:
- Health Physics, Journal Name: Health Physics Journal Issue: 3 Vol. 70; ISSN HLTPAO; ISSN 0017-9078
- Country of Publication:
- United States
- Language:
- English
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