FIELD DETERMINATION OF THE TIME-VARYING EQUILIBRIUM FACTOR BETWEEN RN-222 AND ITS SHORT-LIVED DECAY PRODUCTS IN THE ATMOSPHERE ABOVE A WASTE-ROCK PILE

Short-term measurements (5-min sampling) of Rn-222 and its decay produ cts concentration, and also of the concomitant meteorological paramete rs, were performed on a waste-rock pile (Crossen, Saxony) during the w eek of 17-21 August 1994. As could be expected from measurements made directly above the source, the equilibrium factor is low (mean value a t 0.5m-1.5m, 0.13-0.16), while the daily radon concentration (152-136 Bq m(-3)) and the daily potential alpha energy concentration (0.122-0. 136 mu J m(-3)) are relatively high. The relationships binding these r adiological parameters to the state of atmospheric stability were inve stigated. The concentrations of radon and its daughters increase with the stability of the atmosphere. On the contrary, no detectable trend was found between the variations of the equilibrium factor and the sta te of atmospheric stability. Other parameters, such as wind velocity, dry deposition of radon decay products, but also the aerosol concentra tion in air, must be taken into account to predict the equilibrium fac tor variations. The complexity of studying the outdoor equilibrium fac tor resides in the fact that, besides the necessity to integrate numer ous phenomena, the equilibrium factor value above a finite area source is also influenced by the presence of radon from the regional backgro und. (C) 1996 Elsevier Science Ltd.