Airborne Gamma-Ray Spectrometry: Radon Correction and Mapping

The main geological task of the AGS is to estimate the content of potassium, uranium, and thorium in the near-surface layer. Estimates for potassium and thorium are reasonably straightforward, while estimates for uranium are a complex and important issue due to the presence of radon in the air. Radon, one of the decay products of uranium, is the source of all major gamma emitters of the U-238 family, both in the ground and in the air. It is impossible to distinguish between uranium and radon by the energies in the measured spectra. Without taking radon into account, estimates of the uranium content can be overestimated and contradictory. The estimation of the uranium content taking into account the influence of radon is called the radon correction. There are several known corrections for radon, all based on a comparison of different parts of the spectra. The presence of radon affects the spectra in two ways - the areas of the photopeaks increase and the Compton component of the spectra changes. Here, both of these properties are used to construct two new radon corrections. The first correction uses a standard geophysical environment model that consists of two half-spaces at each data point. The second correction uses the empirically found features of the spectra near the photopeaks. The distance of the influence of field sources, which should be taken into account when averaging the data, is discussed.