Fraction of the Positive ~218Po and ~214Pb Clusters in Indoor Air

摘要

The fraction of the positively charged unattached radon decay Products, ~218Po and ~214Pb in indoor air was determiped by model calculations. The results of the calculations were confirmed by measurements in a test chamber (volume: 8 m~3). The fraction of both radionuclides depends on the attachment parameter (SI) and the neutralization rate (v) in room air. The total removal parameter S~1 velence lambda_l + nu + q~f + X velence lambda_1 C~f_1l/C_0 considers the attachment rate to aerosol particles (D, plate-out rate to room surfaces (q~f) and the ventilation rate (v) (lambda_l: decay constant of ~218Po). The S_1-value of room can be determined by measurement of the concentration of the unattached Z18Po clusters (of) and radon (CO). The neutralization rate (v) in environmental air depends mainly on the ion production rate. The influence of the relative humidity in the range 30-95percent (temperature: 20degC) is negligible. In addition, equal neutralization rates for ~218Po and ~214Pb could be derived. In room air with ion production rates between 5 and 500 nC kg~-1 h~-1 mainly generated by the alpha emitters of radon, thoron and their shortlivef decay products, the fractions for positive 218Po clusters vary between 55 and 17percent and for ~214Pb clusters between 53 and 14percent. For a typical average concentration of radon (50 Bq m~-3) and thoron (10 Bq m~-3) in homes, 48percent of ~218p. clusters and 45percent of if'Pb clusters are positively charged.