— adh.%ast4 5 ‘mmenenurepees C Soeny THE RADIUM-D AIR/SOIL CYCLE AND ITS RELATION TO THE sr AIR/SOIL RATIOS L. B. LOCKHART, JR. In soil radium decays to radon which diffuses into the atmosphere and there reestablishes an equilibrium with its decay products, Ba, TAB and Rac. ‘These’ products in turn decay to the long-lived RaD (Pp 210» 22 years). Due to the short residence time of radioactivity in the lover atmosphere (average lifetime 5-30 days), most ofthe radium-D activity wil be deposited on the ground by natural processes, . in time equilibrium will be established betveen the rate of evalution of Radon from the soil and the rate of deposition of RaD in the soil. The emission of yadon fron the soil and thus the radon concentration in the air | will be the rate-controlling step. — At the present tine effective equilibriua mst have been reached between the average air concentration of radon ‘and the concentration of vedium-D in the soil at any given location. Thus the ratio between these concentrations represents the “coupling” between air and ground et that location and vin include the a effects of fallout, rainout and impaction processes averaged over several _ years. In practice the determination of this ratio will be difficult because most soils contain some uranium (or radium). would be required: A. Experimentally the following procedure» | . | Determine the average radon (or RaB+C) concentration of the air at a oiven location — - : b. Measure the ReD content of a soil sample. ‘the depth to which the soil should be sampled mix mist be determined by running samples representing consecutive @-inch increments in depth. This method would be most accurate in soile of lowest uraniun (radium) content. c. ‘The uranius (preferably the radiun) content of these same samples should be determined. Alternatively, if the soil composition is the same for a considerable