MEASUREMENTS OF THE ACTIVITY-WEIGHTED SIZE DISTRIBUTIONS OF RADON DECAY PRODUCTS OUTDOORS IN CENTRAL NEW-MEXICO WITH PARALLEL AND SERIAL SCREEN DIFFUSION BATTERIES

Interest in deposition of natural atmospheric tracers motivated study of the activity-weighted size distribution of radon (Rn-222) decay pro ducts outdoors. High-flow, large area parallel, and serial screen diff usion batteries were constructed. The combination of a 25 L min(-1) fl ow rate and a 9-cm-diameter collection area allowed measurements of ac tivity-weighted size distributions at ambient radon levels. The measur ements were performed outdoors at two field sites in semi arid south-c entral New Mexico. Spectra show the classical bimodal distributions wi th the first peak between 1 and 2 nm and the second one around 100 nm. No significant activity was detected in the cluster mode of 10 nm.