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Published: 1995

Total Pages: 20

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An aerial radiological survey, which was conducted from March 1 to 13, 1995, covered a 51-square-mile (132-square-kilometer) area centered on the Davis-Monthan Air Force Base (DMAFB) in Tucson, Arizona. The results of the survey are reported as contours of bismuth-214 (214Bi) soil concentrations, which are characteristic of natural uranium and its progeny, and as contours of the total terrestrial exposure rates extrapolated to one meter above ground level. All data were scaled and overlaid on an aerial photograph of the DMAFB area. The terrestrial exposure rates varied from 9 to 20 microroentgens per hour at one meter above the ground. Elevated levels of terrestrial radiation due to increased concentrations of 214Bi (natural uranium) were observed over the Southern Pacific railroad yard and along portions of the railroad track bed areas residing both within and outside the base boundaries. No man-made, gamma ray-emitting radioactive material was observed by the aerial survey. High-purity germanium spectrometer and pressurized ionization chamber measurements at eight locations within the base boundaries were used to verify the integrity of the aerial results. The results of the aerial and ground-based measurements were found to be in agreement. However, the ground-based measurements were able to detect minute quantities of cesium-137 (137Cs) at six of the eight locations examined. The presence of 137Cs is a remnant of fallout from foreign and domestic atmospheric nuclear weapons testing that occurred in the 1950s and early 1960s. Cesium-137 concentrations varied from 0.1 to 0.3 picocuries per gram, which is below the minimum detectable activity of the aerial system.