Equilibrium and Transient Modeling of the Fate and Transport of Radon Progeny

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Dan Steck, Physics


Current radon risk assessments are based on radon gas measurements, which have long been suspected of being inaccurate predictors of effective dose. Using a mass-balance equilibrium model and a Monte-Carlo simulation, correlations were sought between measurable activities other than radon and the effective dose. Separate correlations for high aerosol and low aerosol environments were investigated. Both active filter measurements of airborne activities and passive detector measurements of surface deposited activities were considered. A number of correlations were found that predicted effective dose much more accurately than radon. Theory and measurements indicate that the coefficient of variance of the effective dose as predicted by radon can be reduced by a factor of two using surface deposited activities to predict the effective dose. A factor of four reduction was achieved using direct measurements of airborne attached and unattached 218-Po. Correlations predicting model parameters such as the attachment rate and deposition velocity from surface deposited activities were also investigated, but found to be too inaccurate for reliable use. Transient response times to step function changes to equilibrium room conditions were investigated. While it was previously assumed that activities took about 3-4 hours to come into equilibrium after conditions changed, measurements indicate that the return times to equilibrium after a change in room conditions can range from approximately 6-20 hours.

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