Radioactive cesium discharged from the Fukushima No. 1 nuclear power plant was detected some 100 kilometers from the stricken facility even until late August, research shows.
The finding was announced by a joint research team of the Geochemical Society of Japan, the Japan Geoscience Union and the Japan Society of Nuclear and Radiochemical Sciences.
The cesium concentration remained roughly constant at about 0.01 becquerel per cubic meter of air from June to August, but fell to 0.0001-0.0005 becquerel per cubic meter in late August and did not show up at all by the end of August.
Radioactive iodine, with a half-life of only 8 days, was detected only at a site 100 km from the plant used for measurements through July. No contamination was detected in August.
The study team conducted air measurements at 11 sites within 300 km of the Fukushima plant. It was scheduled to present its findings Oct. 18 at an atmospheric chemistry symposium in Uji, Kyoto Prefecture.