François Diaz-Maurin
On March 14 and 15, 2011—three days after the Great East Japan Earthquake and its resulting tsunami hit the Fukushima nuclear power plant—explosions at two of the plant’s reactor buildings released a huge amount of invisible radioactivity. These radioactive plumes were blown away by the wind, descending over the surrounding area and into the ocean. Eventually, the radiation emitted from the Fukushima plants spread over the entire Northern Hemisphere. It also spread to Japan’s capital, Tokyo.
Following the explosions, Japanese researchers rushed to collect and study radioactive materials from the soil and the air to find out what had happened inside the reactors, believed now to have melted down because their cooling systems failed. On March 13, the Tokyo Metropolitan Industrial Technology Research Institute, the agency responsible for measuring the air quality of particulate matter in the Tokyo area, started to collect air samples more frequently. This effort was part of the Tokyo metropolitan government’s emergency monitoring program for environmental radiation, which aimed to detect gamma-emitting nuclides in airborne dust. The filters revealed that at around 10 a.m. on March 15, 2011, a large plume of radioactivity reached Tokyo, some 240 kilometers (149 miles) south of Fukushima. All samples taken on March 14 and March 15 showed spikes in radioactivity.
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