The gamma ray flux of the 2464 keV line is used to determine the surface concentration of 232 Th. 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. We sampled the flux along highways and town streets in the populated areas of Minnesota. This map reflects approximately 3000 data intervals of 1 to 2 km long. By restricting data acquisition to times of stable weather, the 40K concentrations are reproducible to within 30%.
Questions/Comments, e-mail: Dr. Steck
Last revised : 30 June, 2004
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