Aerial and Ground-Level Gamma-Ray Surveys

Uranium concentration thus determined is usually given in units of ppm eU (parts per million of equivalent uranium) as a raninder that this indirect measurement is based on the daughter nuclide that is assumed to be in secular equilibrium with U-238 (IAEA-TECDOC1363 2003). The data from aerial survey may be corrected for effects arising from the background (cosmic radiation and aircraft radioactivity), altitude (changes in pressure, temperature, and air density effects), the presence of 

Ground-level surveys can be conducted by vehicle-mounted gamma spectrometers or on foot by handheld or portable detectors. A more detailed map may be obtained by these methods than by aerial mapping, but these are more time consuming and labor intensive. In aerial survey, the distance between the surface and the spectrometer is necessarily larger than ground-level inspection and that is reflected by the sensitivity and resolution. 

Gamma ray surveys are useful only for the detection and determination of radionuclides that are close to the surface due to attenuation of the radiation by soil, water, vegetation, and air. Ten meters of air or 10 cm of snow will reduce the radiation intensity by 1% (so from an altitude of 100 m the attenuation in air is 50%) while 2 cm of soil would attenuate 35% of the gamma rays and a 10% increase in soil moisture would increase the attenuation by about 10% (IAEA-TECDOC1363 2003). 

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