Community Research and Development Information Service - CORDIS

Plate out of radon daughter aerosols in domestic and mine environments

A 6-channel, parallel, multiscreen diffusion battery, utilising silicon diffused junction detectors to detect alpha particle emissions from filters downstream from the scrrens, has been used to determine the activity size distribution of the aerosol in the atmosphere of mines and homes to which radon-222 daughters are attached. The battery was modified to allow resolution of the unattached fraction of radon daughters, having diameters in the range 0.5-3 nm. Previously reported measurements of unattached fraction of potential alpha energy concentration (PAEC), fp, in homes have given values of 0.04 to 0.34. Measurements in a kitchen while cooking was in progress yielded a mode with activity median diameter of 11 nm. In living rooms close to kitchens, a mode between 6 and 14 nm occurs during and following cooking. The accumulation mode in the activity size distributions measured had a modal diameter between 110-130 nm. Aerosol conditions in above ground workplaces, (eg schools) were similar to those in homes.

Limited data has been obtained on activity size distributions of radon daughters in mines. In homes, the average radon gas concentration is a better estimate of dose to the lungs than is measurement of average total PAEC, but this is not so in mines. In homes, factors affecting the equilibrium factor, F, and unattached fraction, fp, act in opposite senses, so that increasing fp, which would increase the dose to the lungs, is offset by a falling F, tending to reduce the dose. In mines, because of high aerosol concentrations, independent of varying ventilation conditions, fp is always low (less than 0.02). In homes, an annual average radon concentration of 20 Bqm{-3} results in an effective dose equivalent of 1 mSv.

Reported by

National Radiological Protection Board
OX11 0RQ Didcot
United Kingdom
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