 The explosion was also recorded worldwide by the global monitoring system operated by the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO).Two weeks after the detonation, a CTBTO radionuclide monitoring station in northern Canada detected traces of the radioactive noble gas xenon in the air.Backtracking calculations by analysts at the CTBTO indicated that the xenon particles originated from North Korea and that the explosion had been nuclear in nature.