BY HISAE SATO STAFF WRITER
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.
In Saitama Prefecture, some mountainous areas of Chichibu, located 250 km from the plant, recorded 30,000 to 60,000 becquerels per square meter.
In the 1986 Chernobyl nuclear accident, areas with 37,000 becquerels or more of radioactivity per square meter were designated contaminated zones, while levels of 555,000 becquerels or more required forcible relocation.
In Chiba and Saitama prefectures, the highest radiation levels were 0.2 to 0.5 microsievert per hour. In most other areas, the radiation levels were 0.1 microsievert or less.