Above the Aleutian Islands radioactive particles were found that were contaminated by two different forms of uranium isotopes. Their origin is unknown.
The particles were reported by the NOAA(US National Oceanic and Atmospheric Administration). They appeared in the upper troposphere more than 7km above Alaska. NASA’s WB-57 aircraft took a sample.
The two types are uranium-235 and 238. The second is slightly radioactive and very rare to find that high up. While 235 is ever rarer to find in nature and is commonly found in atomic warheads.
The unusual about this that in 20 years of research never were these particles found.
“The purpose of the field campaign was to obtain some of the first global cross-sections of the concentration of trace gases and of dust, smoke and other particles in the remote troposphere over the Pacific and Atlantic Oceans” the researchers explained.
For anyone interested the above study was published in the Journal of Environmental Radioactivity.