The Comprehensive Test Ban Treaty Organisation (CTBTO), which has 90 monitors around the world to detect radioactivity from nuclear bomb tests, has already detected radiation in neighbouring Russia. Using historical data from Chinese bomb tests, it estimates that it will take a further 10 to 14 days to reach Europe.
Lars-Erik De Geer, research director at the Swedish Defence Research Institute, a government agency, said that iodine and caesium particles had been picked up in Russia. "It is not something you see normally," he said. "But it is nothing to be scared of at all." He said he was convinced they would eventually be detected over the whole northern hemisphere. "In the past when they had nuclear weapons tests in China ... then there were similar clouds all the time without anybody caring about it at all," he said.