The radon generating potential of the soil at a location can be estimated from the surface gamma ray flux of the 1764 keV line of 214Bi, a radon decay product. This spectral line has been used before in a number of studies to estimate the near-surface radon concentration in the soil. For example the nationwide aerial survey conducted as part of the NURE project ( see NURE eU map) has been used by the USGS/EPA to help construct a national map of radon zones ( EPA Rn map). Since we are interested in characterizing surface radon concentrations near houses, our spatial sampling is not uniform nor comprehensive on a statewide scale as the NURE data. However it better samples the radon potential near population centers. We sample along highways and town streets. We developed a carborne system for mapping gamma radiation from soil located next to streets and highways ( Steck, 1993). The radionuclide concentrations were extracted from gamma ray spectra taken by a 7.6 x 7.6 cm NaI detector shielded to view the about 0.3 hectares of surface approximately 10 m beyond the right hand side of the automobile. Spectra were automatically acquired and analyzed by a onboard multichannel analyzer that was driven by batching software. Locations were determined every 40s by a global position receiver coupled to the portable computer. The flux is integrated during for 120 s. Spatial intervals cover 2 km along major highways, 1 km along county roads, and 0.4 km along city streets. By restricting data acquisition to times of stable weather, the 214Bi concentrations are reproducible to within 30%.
Questions/Comments, e-mail: Dr. Steck
Last revised : 30 June, 2004
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