Separation and calculation of Anthropogenic and Natural Dose Rate from Airborne Gamma Ray Spectrometer Data

Geological Survey of Norway (NGU) carries out various geophysical surveys routinely from the ground and the air to strengthen the geological mapping in the country. Radiometry survey using gamma-ray spectrometers is one of such geophysical methods where naturally occurring and anthropogenic radioactive sources are detected.

Recently, NGU has started calculating total dose rate from airborne gamma-ray spectra. Total dose rate is a sum of dose rates from naturally occurring and anthropogenic radionuclides. Therefore, anthropogenic dose rate can be calculated by subtracting the natural dose rate from the total dose rate. We tested separation of anthropogenic dose rate from natural dose rate to find out the areas with man-made radionuclides. Accumulation of the fallout of such man-made radionuclides can happen due to a nuclear accident which can spread to neighboring countries depending on wind and rain conditions at that time. These areas can be found out by airborne surveys and followed up with detailed ground and laboratory-based measurements. We present two examples here, 1) an area in Norway where Cs-137 (an anthropogenic radioisotope) is still present after the Chernobyl nuclear accident in 1986 and 2) another area where only natural radioisotopes are present.