Measurements of the unattached fractions of radon daughters in houses.

Results are presented of the influence of the particle concentration on the activity concentrations of the attached and unattached shortlived radon daughters. The measurements were carried out in rooms of houses in Southern Germany with radon activity concentrations in the range of 150-900 Bqm-3. Consideration of the F factor and the fraction of the unattached daughters fp and comparison with theoretical predictions is one part of the data evaluation. In low (v less than 0.3 h-1) and moderate (0.3 h-1 less than v less than 1 h-1) ventilated rooms the particle concentrations (3*10(-3) - 4*10(4) cm-3), F values (0.2 - (0.2 - 0.3) and the unattached fraction fp (0.05-0.15) were measured. Only rooms with higher particle concentrations or with larger particle sizes due to special aerosol sources (cigarette smoke, cooking, stove heating) showed fp-values less than 0.05. In a second part the attachment rate, the plateout rates and the average attachment diameters of the room aerosols were derived from the measured data by model calculations.