Radioactive particles are mysteriously floating across Europe, leaving everyone baffled, including experts.

The radiation spike was first noticed on the 2nd week of January in Norway, and then it made its way across Finland, Poland, Czech Republic, Germany, France and Spain.

The Barents Observer reported that the radioactive Ionide-131 was initially detected by the air filter station at Svanhovd, which is located a few hundred meters from Norway's border to Russia's Kola Peninsula in the north.

Although it started in Norway, it was Finland and France who went public with the information.

Press release by Institute de Radioprotection et de Süreté Nucléaire (IRSN) noted that Iodine-131 has a short life, which suggests that the radionuclide is released recently.

Iodine-131 is closely associated with atomic bombs. Belfast Telegraph said the same material was found at the Chernobyl and Fukushima nuclear power plants.

As such, theories about the possibility of nuclear weapon testing surfaced. However, scientists noted that the Iodine-131 recently found in Europe was found on its own, which might imply that the radioactive leak did not originate from any nuclear weapon.

The closest hypothesis that experts have is that it came from medical isotope facilities that did not inform the authorities about the leak.

News.com.au reported that the US military has now dispatched to U.K. a nuclear "sniffer plane" called the WC-135 Constant Phoenix, to detect where the radiation is originating.

The report added that the plane was also seen close to North Korea following the country's nuclear missile tests as well as over Japan after the Fukushima power station meltdown.

The US Airforce has not admitted that the aircraft was dispatched for the purpose of detecting the source of radiation, but has admitted that they deployed it.

The Independent quoted a US Airforce spokesperson who said the aircraft is in Europe "on a preplanned rotational deployment scheduled far in advance."

"The WC-135 routinely conducts worldwide missions and we are not going to get into further details," they said.