Deposition behaviour of 222Rn progeny on surfaces

There are many publications on the deposition of radon progeny on surfaces, but majority of these works measured the airborne radon progeny concentration and then deduced the deposited progeny concentrations indirectly. In this work, direct depositions of 222Rn progeny loaded aerosols on different wall coatings were monitored by a silicon α-detector rotating over the coatings. The wall coatings were applied on the inner surface of a small stainless-steel chamber that was connected to a much larger radon chamber. The 222Rn concentration, the potential alpha energy concentration, equilibrium factor and unattached fraction of 222Rn progeny, the aerosol concentration and aerosol size distribution inside the radon chamber were all controlled precisely. The air in the radon chamber was used to feed the small chamber where deposition velocities and recoil fractions of the radon progeny were measured. The deposition velocity of unattached progeny was found to range from 3 to 5 m h-1, being higher at increased air motion. The deposition velocity of attached progeny was about 10 times slower at 0.2–0.5 m h−1 and enhanced deposition by air motion was not as significant. Recoil fractions of unattached and attached 214Po were around 0.50–0.57 and 0.45–0.53, respectively. A slight decrease in recoil fraction of unattached 214Pb was observed at higher air motion.