[ RadSafe ] Radioactive particles from nuclear tests that took place decades ago are persisting in the upper atmosphere,

[Fred BY]

BBC reports

"Radioactive particles from nuclear tests that took place decades ago are
persisting in the upper atmosphere, a study suggests.

Previously, scientists believed that the nuclear debris found high above the
Earth would now be negligible.

However this research shows that plutonium and caesium isotopes are still
present at surprisingly high concentrations.

The work  <http://dx.doi.org/10.1038/ncomms4030> is published in the journal
Nature Communications.

http://www.nature.com/ncomms/2014/140107/ncomms4030/full/ncomms4030.html

Lead author Dr Jose Corcho Alvarado, from the Institute of Radiation Physics
at Lausanne University Hospital in Switzerland, said: "Most of the
radioactive particles are removed in the first few years after the
explosion, but a fraction remains in the stratosphere for a few decades or
even hundreds or thousands of years."

However, he said the levels were not high enough to pose a risk to human
health.

Radioactive hangover

At the height of the Cold War, when the nuclear arms race was in full swing,
weapons were being developed and tested around the world.

But more than 50 years on, their radioactive legacy remains.

While nuclear explosions initially throw material up into the air,
scientists had thought that the radioactive particles would remain for a
limited time.

In the troposphere (the lower layer of the atmosphere that sits directly
above the Earth), the isotopes are removed fairly quickly, as they are
"washed out" by attaching to rain or snow or are drawn down by gravity.

However, in the stratosphere (the layer that sits from about 10-50km above
the Earth), the Swiss team believes that some particles become trapped.

"The concentrations we measured were in the order of about 1,000 to 1,500
levels higher in the stratosphere than in the troposphere," said Dr Jose
Corcho Alvarado.

While the tests were carried out over Switzerland, the team said they
expected similar levels would be found at the same latitude elsewhere around
the world.

The scientists also found that this material can be moved around in the
atmosphere by natural events such as volcanic eruptions.

For example, in 2010 after Iceland's Eyjafjallajökull volcano erupted,
plutonium levels in the lower atmosphere increased.

While scientists say the long-term effects are not clear, the lead author Dr
Jose Corcho Alvarado said: "It is important to say that this is not
dangerous for the population."

He added that the nuclear debris could be tracked to find out more about how
particles in the atmosphere move around."

http://www.bbc.co.uk/news/science-environment-25641310