What can gross alpha/beta activities tell about 210Po and 210Pb in the atmosphere?

Abstract

210Po and 210Pb represent the most abundant part of atmospheric aerosol long-lived natural radioactivity. Moreover, 210Pb-210Po monitoring in the atmosphere can be of interest for tracking extreme natural events that can enhance the level of alpha/beta radioactivity in air. In this paper, we question the possibility to use routine gross alpha/beta measurements in order to monitor 210Po, 210Pb and 210Po/210Pb ratio in the atmosphere. Based on joint gross alpha/beta measurement and 210Pb-210Po specific determination on 16 atmosphere samples, we show that (i) gross beta activity systematically overestimates 210Pb activity due to the presence of interfering beta emitters and (ii) gross alpha activity mostly reflects 210Po activity even if an underestimation is always observed due to alpha particle attenuation in the sample. In order to determine 210Po/210Pb ratio, we discuss the advantages of using gross alpha activity time variation compared to specific 210Po measurements. Finally, the gross alpha/beta ratio appear to be a good proxy of the 210Po/210Pb ratio when large-scale variations are to be monitored. We report a first reference level for the activity level of airborne 210Po in France of 13 ± 6 μBq/m3.