Remember that mysterious radioactive cloud that fell over much of Europe at the end of September? A recent analysis by France’s Institute of Radiation Protection and Nuclear Safety (IRNS) placed the source of the leak with some confidence on the border of Kazakhstan and Russia – and it seems that they were absolutely spot on.

The cloud emerged from a facility in Chelyabinsk, a part of Russia fairly close to Kazakhstan that is most famous for its rendezvous with a rather powerful meteor back in 2013. The village of Argayash has been revealed to have experienced the most significant amount of radiation, that which exceeded the natural background levels by 986 times.

Rather curiously, the reason we absolutely know that the radiation first emerged from Chelyabinsk is that Russia – a notoriously secret state – has admitted to detecting the radioactive leak themselves.

“Probes of radioactive aerosols from monitoring stations Argayash and Novogorny were found to contain radioisotope Ru-106” between September 25 and October 1,” Rosgidromet, Russia’s meteorological agency, said.

This was a curious admission of truth, considering that not too long beforehand, Rosatom – the state-owned nuclear corporation – said that no traces of ruthenium-106 had been found anywhere in Russia except trace amounts in Saint Petersburg.

The radiation cloud was primarily comprised of ruthenium-106, something that is produced during nuclear fission reactions. The lack of other radionuclides suggests it wasn’t some sort of reactor explosion but an accidental leak from a medical or storage facility of some sort.

A few weeks back, the IRNS said that so much radiation would have been dumped around the source of the cloud that a rapid evacuation would have been necessary to save lives. The rest of Europe, incidentally, was never at risk of any sort of significant contamination – the short half-life of ruthenium-106 meant that by early October it could no longer be detected across the continent.

A precise location of the leak is still forthcoming, but it’s notable that the heavily irradiated Argayash is close to the Mayak nuclear facility, one which produces plutonium and reprocesses nuclear waste. Mayak is already infamous for the 1957 Kyshtym disaster in which radioactive matter was spread over an area where 272,000 people lived, and it now seems likely that this is the source of the most recent troublesome plume.

It’s not clear what the next steps will be, but plenty of concern abounds for those living in Argayash. At this point, it remains unknown whether they were evacuated following the leak, and if not, how badly they may have been contaminated.

[H/T: The Guardian]