Determination of the source location of anthropogenic radionuclides collected in Finland and Sweden in June 2020 using a multi-technology analysis.

In June 2020, observations of anthropogenic radionuclides in Estonia, Finland, and Sweden that were not related to any acknowledged environmental release led to a comprehensive investigation on the source and cause of the unusual emissions. Several of the observed radionuclides were on the list of Comprehensive Nuclear-Test-Ban Treaty (CTBT) relevant radionuclides as an indicator of a potential nuclear test, and warranted detailed investigation. While analysis of aerosol samples coupled with Atmospheric Transport and Dispersion Modelling (ATDM) is a standard approach for environmental particulate releases, several new techniques were employed to better characterize the samples that allowed for useful inferences to be made. These inferences were crucial in forming the ultimate hypothesis for determining the facility type and location of the release.