Airborne gamma-ray spectrometry for large-scale radiological mapping on the example of the chornobyl exclusion zone

In consequence of the 1986 accident at the Chornobyl Nuclear Power Plant, the so-called Chornobyl Exclusion Zone (ChEZ) was established, rendering the most highly contaminated areas in the vicinity of the accident site inaccessible to the public. In 2021, the German Federal Office for Radiation Protection (Bundesamt für Strahlenschutz) was invited to conduct a measurement campaign in order to produce a recent comprehensive large-scale radiological map of the ChEZ. During the two weeks long campaign an area of 3300 km² was radiologically mapped using helicopter-borne gamma-ray spectrometry. As a result, contamination maps of the ¹³⁷Cs inventory in soil and the calculated ambient gamma dose rate for the ChEZ were generated. Those results were assessed from the airborne measurements' data using auxiliary data from soil sampling. Additionally, the results of the helicopter-borne measurements in 2021 were compared to radiation levels assessed shortly after the accident in 1986. Overall, the created contamination maps and the comparison with former surveys show that the distribution of ¹³⁷Cs is mostly as it was shortly after the accident. As of now, the gamma dose rate in the ChEZ is predominated by the contribution of ¹³⁷Cs.