Japan Soil Measurements Surprisingly High, Science Magazine, March 25, 2011:
The levels are highest from two points northeast of the plant, ranging from 8690 becquerels/kilogram to a high of 163,000 Bq/kg measured on 20 March from a point in Iitate about 40 kilometers northwest of the Fukushima plant. …
The soil measurements are more significant for evacuation purposes than radioactivity in the air, says nuclear engineer Shih-Yew Chen of Argonne National Laboratory in Illinois, because cesium dust stays underfoot while air is transient. …
Based on a rough estimate, a person standing on soil with 163,000 Bq/kg of cesium-137 would receive about 150 millisieverts per year of radiation, says Chen. This is well above the U.S. Environmental Protection Agency standard of 50 millisieverts per year for an evacuation. (Per day, it’s 0.41 millisieverts, which is equivalent to four chest x-rays.) But Chen adds, “one point [of data] doesn’t mean that much.”
The hot spot is similar to levels found in some areas affected by the 1986 Chernobyl nuclear reactor accident in the former Soviet Union. Assuming the radiation is no more than 2 centimeters deep, Chen calculates that 163,000 Bq/kg is roughly equivalent to 8 million Bq/m2. The highest cesium-137 levels in some villages near Chernobyl were 5 million Bq/m2.
Read the report here.
Published: March 26th, 2011 at 3:59 pm ET