It was a nuclear whodunit: A cloud of radioactive material was hanging over Europe, but no one knew where it was coming from.
The plume persisted for a few days in September and October 2017, detected by a network of atmospheric monitoring sites across Europe. Although not at levels dangerous to human health, the cloud was enough to raise alarm before dissipating.
“We were stunned,” says radioecologist Georg Steinhauser of Leibniz University Hannover in Germany. “We had never seen anything like this before.”
Shortly after the detection, scientists speculated that a nuclear facility in Russia, the Mayak Production Association near Ozersk, was the source. Now, in a study published online July 26 in the Proceedings of the National Academy of Sciences, Steinhauser and colleagues have laid out evidence supporting that claim. The cloud may have been released in a failed attempt to create highly radioactive material for an experiment in Italy on neutrinos, subatomic particles that are spit out in certain types of radioactive decay, the team says.