Wednesday, September 28, 2011

New radiation maps from Japan

Ex-SKF reports on new official radiation maps of parts of Japan issued by the Government. Notice that metropolitan Tokyo is excluded even if dangerous radiation levels affect some areas.

Environmental radiation (in micro-sieverts/hr):

The color code may be quite misleading, however it is difficult to evaluate: 5 micro-sieverts may be like an X-ray but an X-ray every hour will kill you soon.

The generally accepted limit for civilians is 1 mSv/year (1 mSv=1000 micro-Sv). An X-ray per hour (within the yellow zone) will reach this safety limit in 200 hours (less than 9 days). In the green zone it will take less than 1000 hours (42 days).

In the middle blue zone it takes 5,000-10,000 hours (around a year), so this area and the deep blue one are the only ones barely safe by normal standards. Light blue to red should be declared evacuation zone, at least for children.

Green here does not mean safe, just less immediately deadly. In fact all the green zone should be totally evacuated, I understand.

For comparison and, specially because it sets no artificial border at Tokyo, this other map compiled by Prof. Hyakawa (overall similar with the official one):

Also the color code is less optimistically green and more objectively reddish. Still all that is colored has unacceptable levels of radiation for civilian life.

Cesium-134 and cesium-137 (in Bequerels/m²):

This kind of mapping, even if similar in the results has the advantage that it can be compared almost directly with Chernobyl exclusion zone maps like this one:

Curies (Ci) can be directly converted to Becquerels and vice versa:

1 Ci = 3.7×10¹⁰ Bq = 37 GBq

(For those unfamiliar with the IS, 1 Km² = 10⁶ m²)

So 1 KBq/m²  =  1 GBq/Km²

  • 37 KBq/m² = 37 GBq/Km² = 1 Ci/Km² (within the gray zone in Japan) - Unnamed zone low limit
  • 185 KBq/m² = 185 GBq/Km² = 5 Ci/Km² (within the grey-blue zone) - Periodic control zone low limit (includes most of Fukushima Pref.)
  • 555 KBq/m² = 555 GBq/Km² = 15 Ci/Km² (within the light blue zone) - Permanent control zone low limit (includes urban areas in Fukushima Pref.)
  • 1480 KBq/m² = 1480 GBq/Km² = 40 Ci/Km² (within the yellow zone) - Closed zone

The Chernobyl evacuation scheme is anyhow quite questionable. The civilian exposure limit is much lower than what they'd get living in the 'Unnamed Zone'.  That's why there are still so many radiation victims, specially among Children. Yet some crackpots like former Ukranian President Viktor Yushenko who want to do as in Japan and get the polluted lands back to the economy, spreading radiation all around.

Curiously enough there are areas in the current, geometric, exclusion zone that are relatively safe. This is something that the people at Safecast did notice as well. But their latest drive through the exclusion area (different roads) yields unbearable radiation measures.

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