23,300 Bq/Kg of Radioactive Cesium from a Mix of Wet Soil and Dead Leaves in Mizumoto Park in Tokyo

(Sorry, you can't just multiply the number by 65 and compare it to the Chernobyl evacuation level. Read on to find out why.)

The Mizumoto Metropolitan Park is located in the eastern Tokyo with elevated radiation levels. The Communist Party delegation of Tokyo Metropolitan Assembly, who has done the survey of radiation levels in Tokyo from very early on in the nuclear crisis, released the result of the latest survey in one of the Metropolitan parks in Tokyo.

The survey found 23,300 becquerels/kg of radioactive cesium from a wet mix of dirt and dead leaves in one location in the Mizumoto Park in Katsushika-ku, Tokyo (No. 4 location in the table posted below).

The delegation did three tests at this location with 2 samples taken on February 15. The third test was done on February 18 by combining the two samples taken on February 15 and tested on February 16 and 17.

It may be important to note that the Communist Party delegation tested the top 1 centimeter of the soil, and the top 1 to 2 centimeters of the soil and dead leaves mixture. The measured numbers may therefore be higher than the samples taken from the top 5 centimeters, which is a normal procedure in the government tests.

To derive "becquerel/square meter" from "becquerel/kg", you multiply "becquerel/kg" number by 65, but that only applies if the soil is taken from the top 5 centimeters. (Ibaraki Prefecture's measurement page as reference, here.)

From the Communist Party delegation of Tokyo Metropolitan Assembly website (English translation is mine; the last two rows are the reference):

According to Yomiuri Shinbun article (2/22/2012), "the Ministry of Education and Science sets the standard of radiation that requires decontamination as locations that test "1 microsievert/hour higher than the surrounding areas", and the Tokyo Metropolitan Bureau of Environment says "There is no need for decontamination at this point.""

Never mind that the Ministry of Environment's decon standard is 0.23 microsievert/hour.

The surface radiation levels and the air radiation levels at 1 meter off the ground all exceed 0.23 microsievert/hour. The highest surface radiation level was 1.54 microsievert/hour, and the highest radiation level at 1 meter was 0.74 microsievert/hour.

Before the nuclear accident, the average background radiation level in Tokyo was slightly above 0.03 microsievert/hour. That was the level right before something very radioactive arrived from Fukushima on March 15, 2011 sometime between 4AM and 4:59AM. (See the Tokyo Metropolitan government's own measurement, here, as the radiation in Shinjuku went from 0.0347 microsievert/hour average between 3AM and 3:59AM to 0.1 microsievert/hour average in the next hour. )

What the Tokyo Metropolitan government needs to do is to scrape 1 centimeter of the soil under the trees and shrubs and remove dead leaves to lower the radiation. But they openly say they are not going to do anything.

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(UPDATE from Kontan Bigcat on Twitter: the 65 multiplier applies only to soil taken from 5 centimeters AND with the soil density (dry) of 1.3 gram/cubic centimeter.

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