Aeroradiometric measurements in the framework of the Swiss ARM25 and International AGC25 Exercises

This document reports on the aeroradiometry measurement exercises conducted in Switzerland in 2025. Measurements were performed between the 27th of May 2025 and the 6th of June 2025 and were structured into two campaigns. The first campaign, ARM25, comprised routine airborne gamma-spectrometry surveys over Swiss nuclear facilities located in Mühleberg and Gösgen. These surveys were carried out on behalf of the Swiss Federal Nuclear Safety Inspectorate (ENSI) in the vicinity of the Gösgen nuclear power plant and the Mühleberg plant, currently in decommission. Outside the operational areas, no radioactivity exceeding natural background levels was detected. No deviations were observed compared with results from previous years. The second campaign consisted of a week long international exercise, AGC25, hosted in Switzerland and coordinated by the Swiss expert group for airborne gamma spectrometry (FAR). Airborne gamma-spectrometry measurements using helicopters and drones were performed by national teams from Switzerland, Germany, France, the Czech Republic and Lithuania. Ground-based measurements were performed by the Swedish observer team in coordination with the exercise organisers. Switzerland contributed to the helicopter surveys with two teams, respectively managed by the National Emergency Operations Centre (NEOC) and the Nuclear, Biological, Chemical Defence and Explosive Ordnance Disposal Centre of Excellence (NBC-EOD). For the first time, an international exercise included source search operations using drones, in addition to helicopters. The exercise demonstrated successful multinational coordination, efficient implementation of composite mapping techniques, and effective localisation, identification and quantification of radionuclide sources. Overall, the campaign strengthened operational readiness, enhanced interoperability with partner nations, and confirmed the high level of training and technical capability among the personnel involved in aeroradiometry.