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15 avril 2011 5 15 /04 /avril /2011 23:04


Fukushima related measurements - Source CTBTO ( Preparatory Commission for the Comprehensive Nuclear-Test-Ban Organization)



- Update 13 April: radioactivity also measured in the southern hemisphere -


Since the double disaster of the 9.0 magnitude earthquake and tsunami that affected hundreds of thousands of people and seriously damaged the Fukushima Daichi power plant in Japan on 11 March 2011, minute traces of radioactive emissions from Fukushima have spread across the entire northern hemisphere. A monitoring network designed to detect signs of nuclear explosions picked up these traces from the stricken power plant.

To date, more than 35 radionuclide stations that are part of the International Monitoring System  have provided information on the spread of radioactive particles and noble gases from the Fukushima accident. The IMS is a global network that will comprise 337 facilities when complete. Sixty-three of the 80 planned IMS radionuclide stations are already operational and able to detect airborne radioactivity.

Initial findings

The first analysis results of the monitoring data became available a few days after the accident. A clear picture quickly emerged. Initial detections of radioactive materials were made on 12 March at the Takasaki monitoring station in Japan just 250 km away from the troubled power plant. The dispersion of the radioactive isotopes could then be followed to eastern Russia on 14 March and to the west coast of the United States two days later.

Spreading across the entire globe


Click here for a simulation of the dispersion of radioactivity (German website by the German Federal Institute for Geosciences and Natural Resources)


Nine days after the accident, the radioactive cloud had crossed Northern America. Three days later when a station in Iceland picked up radioactive materials, it was clear that the cloud had reached Europe. By day 15, traces from the accident in Fukushima were detectable all across the northern hemisphere. For the first four weeks, the radioactive materials remained confined to the northern hemisphere, with the equator initially acting as a dividing line between the northern and southern air masses. As of 13 April, radioactivity had spread to the southern hemisphere of the Asia-Pacific region and had been detected at stations located for example in Australia, Fiji, Malaysia and Papua New Guinea.

Findings confirm Fukushima release

Click for further information (in German by the German Federal Radiation Protection Agency)

The CTBTO’s monitoring system, custom-tailored to detecting nuclear explosions, can detect a range of radioactive isotopes, among them Iodine-131 and Caesium-137. Looking at the ratios between the various radioactive isotopes – in particular Caesium-137 – enables the source of the emission to be identified. In the case of the current readings, findings clearly indicate radionuclide releases from a damaged nuclear power plant, which is consistent with the recent accident at Fukushima in Japan. As of 13 April, the average level of radioactivity picked up by the stations worldwide continued to decline, which is also due to the relatively short half-lives of Iodine-131 (8 days) and Xenon-133 (5.2 days).

The CTBTO’s radionuclide stations are designed to register minuscule amounts of radioactive particles and noble gases – down to a number of a few atoms. The system’s sensitivity is second-to-none - it can detect a concentration of 0.1 g of radioactive Xenon evenly distributed within the entire atmosphere of the Earth. A rooftop detector at the CTBTO’s headquarters in Vienna still catches traces of emissions from the 1986 Chernobyl disaster.

Benefits for disaster mitigation efforts

The IMS is being built to ensure compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT), which bans all nuclear explosions. CTBTO monitoring data and technologies, however, offer a host of additional benefits, particularly in relation to disaster mitigation. One of these benefits is already in place – the contribution of data to  tsunami warning efforts. In 2006, Member States mandated the CTBTO to provide seismic and hydroacoustic monitoring data directly to tsunami warning centres. Data is currently provided to eight tsunami warning centres mainly in the Indo-Pacific region.

Data were also made available to Japan when it was hit by the massive earthquake on 11 March. Tens of thousands of people were tragically killed by the tsunami; still many were saved due to the rapid alerts. According to Japanese authorities, CTBTO data helped them to issue tsunami warnings within a few minutes, thus allowing many people to escape to higher grounds.

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