Saturday, October 8, 2011

Tokyo Metropolitan Government Measures Soil Contamination in Shinjuku

And it is higher, much higher than the Ministry of Education's aerial survey indicates.

First, to recap, according to the just released Ministry of Education's aerial survey of radioactive cesium deposition in Tokyo, most of Tokyo has less than 10,000 becquerels/square meter of radioactive cesium, with the exception of the western-most Okutama and the eastern special wards ("ku") bordering Chiba Prefecture to the east.

Now, it turns out that the Tokyo Metropolitan government, who is not so eager to measure anything radioactive since March 11, was doing its annual survey of soil contamination in Shinjuku and quietly released the data on September 20.

The soil sample was taken at Tokyo Metropolitan Institute of Public Health in Hyakunin-cho, Shinjuku-ku, as it has always been done. (That's where the official air radiation level is monitored every day for Tokyo.)

For the last 5 years, radioactive iodine and cesium-134 were not detected, and cesium-137 was 2 to 3 becquerels per kilogram.

Now, this year, the numbers for the soil from the surface to 5 centimeters deep were:

  • Iodine-131: ND

  • Cesium-134: 360 becquerels/kg

  • Cesium-137: 430 becquerels/kg

  • Total cesium: 790 becquerels/kg

To convert from "per kilogram" to "per square meter", Japan's Nuclear Safety Commission uses the factor of 65. The total cesium per square meter in Shinjuku therefore is: 51,350 becquerels per square meter.

Even if you just take cesium-137 (for comparison purpose), 430 becquerels/kg translates to 27,950 becquerels/square meter.

The Tokyo Metropolitan government also found cesium-134 and cesium-137 in the soil between 5 and 15 centimeters deep. For the past 5 years, iodine-131 and cesium-134 were ND, and cesium-137 was 2 to 3 becquerels/kg.

But this year:

  • Cesium-134: 4.2 becquerels/kg

  • Cesium-137: 7.1 becquerels/kg

  • Total cesium: 11.3 becquerels/kg

However, true to form, the Tokyo Metropolitan government says it is in agreement with the Ministry of Education's survey of air radiation level. The government says the air radiation at the sample location is not that high (0.07 microgray/hr) therefore no decontamination of a wide area will be necessary. (Mr. Governor, we are talking about soil deposition here, not the air radiation level.)

The air radiation the Institute measures at 18 meters off the ground was 0.0563 microgray/hr that day, according to the announcement. The Tokyo Metropolitan government uses microgray as equivalent to microsievert.

It goes to show that the aerial survey with 300 to 600 meter radius and averaging out the numbers doesn't locate high radiation hot spots in the cities like Tokyo or Yokohama. Or anywhere else for that matter. And this Shinjuku location is not considered to be particularly hot.

Here's the screen capture of the Tokyo Metropolitan government announcement, with highlight:

(H/T for the info and the screen capture)


Anonymous said...

Canaryback beat...

One thing is learn and understand what all this Iodine and other engineering words means and another is simply say this is safe or not.

Factual DATA Numbers coming from governments tend to be far from reality, so at this point, we know that this is really wrong but everyone hopes to escape with no risk at all, from this crisis, specially poeple living in Tokyo.

Anonymous said...

why do they start using greys and rads! werent microsieverts, reotegens and cpm good enough!!
sounds like the waters are being muddied if you ask me....5.65 rads eh!! thats not low is it?? its easier than using the gray scale with all them zeros

Anonymous said...

Last year 0.000 becquerel/m2 ,
Official Yesterday 10.000 becquerel/m2
New Shinjuku-ku 51.350becquerel/m2.
Yamauchi / Watari area 15.405.000 becquerel/m2

How many zeroes are missing?

Anonymous said...


Darth3/11 said...

Am I the only one who suspects the entire "solution" of scraping off vast quantities of contaminated topsoil is the worst sort of scapegoating? It seems complete lunacy. Does not solve anything. Creates a huge problem (Where does the soil go? How to safely ship it to a destination? What happens to land now missing its topsoil?). Seems to me the best idea is to simply leave the ground alone. Live elsewhere for the next few decades. In heavily hit places like Iitate, there is no going back. Nonetheless, I predict people will doggedly move back. Only later will the predictable effects clock in...

Anonymous said...

The story of Antarctica's Nukey Poo

Tsutomu Okoba said...

> Darth3/11
I completely agree with you. The only solution is 'throwing away and escaping from the contaminated area.'

The reactors have not yet cooled down. They are emitting extraordinary amounts of radioactivity with vapor. Even though scrap the surface, radioactivity will fall everyday. It wastes time and money and children will suffer from radiation damage while doing so.

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