Fairly high levels of accumulated radioactive cesium in Chiba and Saitama prefectures were shown in a new contamination map released by the science ministry on Sept. 29.
The two prefectures, neighboring the municipal areas of Tokyo, are located about 200 kilometers from the disabled Fukushima No. 1 nuclear power plant. The measurements for Chiba and Saitama prefectures were taken from Sept. 8 to Sept. 12 using helicopters.
In Chiba Prefecture, the highest levels of cesium-137, between 30,000 and 60,000 becquerels per square meter, were detected in northern areas, such as Kashiwa, Matsudo, Abiko and Nagareyama. Cesium-137 has a half-life of 30 years.