Nuclear weapon test debris 'persists' in atmosphere

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. via Pocket http://www.bbc.co.uk/news/science-environment-25641310#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa