We have some new information and many new questions that have arose out of our crowd sourced research today. Concerns initially focused on the Maria medical reactor in Poland and the Rosatom medical reactor in Russia. They are not completely ruled out but radiation mapping along with weather are making them sound less likely. Another potential candidate is the research reactor at Moscow university. It does not specifically state a medical isotope program there but there is the potential for a leak or undocumented experiments, so this one is a distant contender.

One potential source is the Krsko nuclear power plant in Slovenia. In looking at the available data for EURDEP and the reports from other countries this appears to be a location of higher levels of Iodine 131 and also Cesium 137 found at monitoring stations near the plant. The iodine 131 levels near the plant are also relatively high and create a path of traces of radiation going north from the plant area. Cobalt 60 was also detected near the plant.

EURDEP shows ...

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Source: simplyinfo.org