Measurements of unattached and attached RaA atoms in atmosphere and their deposition in human respiratory tract

For evaluating the unattached fraction f (fraction of RaA atoms unattached on aerosols) in the open air, the total activities and the unattached activities of RaA atoms have been measured in various environments. The observation of the fraction g (fraction of neutral RaA atoms among unattached RaA atoms), and the number concentration Z and mean radius of aerosols have also been carried out simultaneously. The observed values of f and g were 0.1 -- 1.0 and 0.65 +- 0.16, respectively. The inverse correlation between f and Z has been observed and discussed theoretically taking account of the fraction g and mean radius of aerosols. The Gormley and Kennedy formula was used for estimating the deposition fraction of unattached RaA atoms in the human respiratory tract, and the Takahashi and Ito model was applied for attached RaA atoms. The calculated results showed that unattached RaA atoms were deposited in the ''upper respiratory passages'' and attached ones in the ''lower respiratory passages'', and that the regional distribution of deposited RaA atoms depended markedly on f. (author)