<p>Radioactive debris caused by nuclear bomb tests during the Cold War still exist in the Earth's atmosphere, a new study has warned.<br /><br /></p>.<p>Scientists previously believed that nuclear debris high above the Earth would now be negligible.<br /><br />The research, however, found that plutonium and caesium isotopes are still present at surprisingly high levels, 'BBC News' reported.<br /><br />"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," lead author Dr Jose Corcho Alvarado, from the Institute of Radiation Physics at Lausanne University Hospital in Switzerland, said.<br /><br />However, according to Alvarado, the levels were not high enough to pose a risk to human health.<br /><br />Researchers said that 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.<br /><br />However, more than five decades after, their radioactive legacy remains.<br /><br />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.<br /><br />However, in the stratosphere - the layer that sits from about 10-50km above the Earth - some particles become trapped, researchers said.<br /><br />Researchers said they expected similar levels would be found at the same latitude elsewhere around the world, the report said.<br /><br />Scientists also found that this material can be moved around in the atmosphere by natural events such as volcanic eruptions.<br /><br />The study was published in the journal Nature Communications.</p>
<p>Radioactive debris caused by nuclear bomb tests during the Cold War still exist in the Earth's atmosphere, a new study has warned.<br /><br /></p>.<p>Scientists previously believed that nuclear debris high above the Earth would now be negligible.<br /><br />The research, however, found that plutonium and caesium isotopes are still present at surprisingly high levels, 'BBC News' reported.<br /><br />"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," lead author Dr Jose Corcho Alvarado, from the Institute of Radiation Physics at Lausanne University Hospital in Switzerland, said.<br /><br />However, according to Alvarado, the levels were not high enough to pose a risk to human health.<br /><br />Researchers said that 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.<br /><br />However, more than five decades after, their radioactive legacy remains.<br /><br />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.<br /><br />However, in the stratosphere - the layer that sits from about 10-50km above the Earth - some particles become trapped, researchers said.<br /><br />Researchers said they expected similar levels would be found at the same latitude elsewhere around the world, the report said.<br /><br />Scientists also found that this material can be moved around in the atmosphere by natural events such as volcanic eruptions.<br /><br />The study was published in the journal Nature Communications.</p>