The missing radionuclides from North Korea’s nuclear test

Science : In 2006, when North Korea carried out its first nuclear test, a US plane detected radionuclides—faint wind-borne traces of radioactive elements such as xenon from nuclear explosions—within days, and a Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) monitoring station as far away as Yellowknife in Canada picked them up 12 days after the test.North Korea declared on 25 May that it had carried out a second underground nuclear test—a blast that clearly showed up on seismometers across the globe.But at a scientific conference during the summer, the CTBTO revealed that its global network of radionuclide detectors had not picked up anything it could pin on the Korean test, nor had the South Koreans or another US Air Force plane.Researchers are speculating that the test occurred deep underground and in rock that melts easily, forming a seal around the explosion chamber and limiting the release of radionuclides.