https://www.usgs.gov/publications/modern-aerial-gamma-ray-spectrometry-and-regional-potassium-map-conterminous-united
Aerial gamma-ray surveys of the natural environment measure the flux of gamma rays produced by the radioactive decay of 40K, 214Bi, and 208Tl in the upper...
gamma ray spectrometrymodernaerialregionalpotassium