© Lassina Zerbo/Twitter
The subtle radiation spike - at levels that are considered harmless to humans, but significant enough to be picked up by radiation monitoring stations - began to make headlines last week, with European authorities announcing new readings of human-made radionuclide particles in the atmosphere.
"Very low levels of the radioactive substances cesium-134, cesium-137, cobalt-60 and ruthenium-103 were measured," the Swedish Radiation Safety Authority tweeted on Tuesday.
"The levels measured are so low that they pose no danger to people or the environment."
Similar observations were also made by radiation protection authorities in Norway and Finland.
Later in the week, Lassina Zerbo, the Executive Secretary of the Comprehensive Nuclear-Test-Ban Treaty Organisation, tweeted a map outlining the possible source region of the anomaly, most of which was territory inside Russia, but also parts of Finland, Sweden, Denmark, and Norway.
Comment: A 4.8 magnitude earthquake struck southeast France on November 11 last year, causing an unusual crack in the Earth's crust, puzzling scientists.