Thursday, April 7, 2011

#Radiation in Japan: "It's Safe" Governments Say, But Is It?

Specifically, my questions are:

  • What do they measure?
  • Where do they measure?
  • How are the results presented?

So Here's two examples, Yokohama City in Kanagawa Prefecture, and Iitate Village in Fukushima Prefecture.

First, Yokohama City Government ( [h/t anonymous reader]:

  • What: gamma ray radiation in the air
  • Where: on top of the 5-story building to avoid the reflection of the radiation on the ground surface and the blockage of the radiation by buildings
  • How: gamma ray radiation in nano Gray (nGy)/hr

That's the only measuring spot for the entire Yokohama City done by the Yokohama municipal government. It could be under-measuring (by avoiding surface reflection) or over-measuring, but one thing is for sure: top of the 5-story building is not where most residents of Yokohama live and work.

Their latest result (April 7): 40 nGy/hr, which equals 0.032 micro-sievert/hr if it is only about external radiation exposure. nGry and micro-sievert are considered more or less equal otherwise.

0.032 micro-sievert/hr x 24 hours = 0.768 micro-sievert/day
1.92 micro-sievert/day x 30 days = 23.04 micro-sievert/month
57.6 micro-sievert/month x 12 months = 276.48 micro-sievert/year

Yokohama's data measures only the external exposure through air, while the internal exposure (through breathing and eating food) is much greater in Kanto according to Prof. Takeda of Chubu University.

At least Yokahama City government doesn't say on their webpage that "it is safe".

Moving on, here's Fukushima's Iitate Village measurement by the Fukushima Prefectural Government (

  • What: The page doesn't say. I assume it is measuring gamma rays.
  • Where: Iitate Village hall
  • How: in micro-sievert/hr

The latest result for Iitate Village (April 7): 5.89 micro-sievert/hr

5.89 micro-sievert/hr x 24 hours = 141.36 micro-sievert/day
141.36 micro-sievert/day x 30 days = 4,240.8 micro-sievert/month, or 4.24 milli-sievert/month
4,240.8 micro-sievert/month x 12 months = 50,889.6 micro-sievert/year, or 50.89 milli-sievert/year.

Fukushima Prefectural Government says:


The radiation dose of one X-ray is 600 micro-sievert. The highest measured today was in Iitate Village, but the number for Iitate Village is well below the X-ray dose level and considered safe.

Here you go. It's safe.

In Iitate Village, the radiation was much, much higher from March 15 (after the Reactors 3 and 4 had explosions). The highest was 44.70 micro-sievert/hr at 6:20PM JST on March 15, and was above 10 micro-sievert/hr until March 26. (You can see it for yourself in this; It's in Japanese, but the 3rd column after the time column is Iitate Village) If the average was 20 micro-sievert/hr, in 10 days or so, the cumulative radiation may have been 5.28 milli-sievert, in 10 days.

That's more than 8 X-rays, without protection, without consent.

The safety limit for radiation exposure in Japan is still 1 milli-sievert for ordinary people.

The radiation control zone in a nuclear facility is so designated where the radiation is more than 0.6 micro-sievert/hour.

Ah minor details. The Japanese government seems set to raise the safety limit to 20 milli-sievert/year from the current 1 milli-sievert/year.

In other words, every man, woman, child, baby is now a nuclear plant worker, like it or not. And God only knows for how long.


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