Field determination of the time-varying equilibrium factor between 222Rn and its short-lived decay products in the atmosphere above a waste-rock pile

Abstract

Short-term measurements (5-min sampling) of 222Rn and its decay products concentration, and also of the concomitant meteorological parameters, were performed on a waste-rock pile (Crossen, Saxony) during the week of 17–21 August 1994. As could be expected from measurements made directly above the source, the equilibrium factor is low (mean value at 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 μJ m −3) are relatively high. The relationships binding these radiological parameters to the state of atmospheric stability were investigated. 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 state of atmospheric stability. Other parameters, such as wind velocity, dry deposition of radon decay products, but also the aerosol concentration in air, must be taken into account to predict the equilibrium factor variations. The complexity of studying the outdoor equilibrium factor resides in the fact that, besides the necessity to integrate numerous phenomena, the equilibrium factor value above a finite area source is also influenced by the presence of radon from the regional background.