# 5417
NHK World News this morning is reporting that radiation readings some 30 kilometers northwest of the Fukushima nuclear facility over the past two days have been measured above 150 microsieverts per hour.
This is well outside of the Japanese evacuation zone (20 km) and on the outer cusp of the `stay indoors’ (20-30 km) zone.
First the NHK News article, then I’ll be back with more on relative radiation doses.
High radiation detected 30km from nuke plant
Friday, March 18, 2011 17:38 +0900 (JST)
Japan's science ministry says relatively high radiation levels have been detected on 2 consecutive days about 30 kilometers northwest of the quake-damaged Fukushima Daiichi nuclear power plant.
The radiation measured 170 microsieverts per hour on Thursday and 150 microsieverts on Friday.
Chief Cabinet Secretary Yukio Edano says the government will take appropriate measures if this level of contamination continues in the area for a long period. But he says this would be unlikely.
Before anyone is tempted to head down to the bunker, it should be noted that people staying indoors in this region are likely experiencing a much lower exposure than these readings might suggest.
Theoretically, at 150 microsieverts an hour, over 24 hours a person would receive about 3.6 millisieverts of radiation – or about what much of the world’s population receives in background radiation every 1.5 to 2 years.
But to put that into perspective, an abdominal CT-Scan exposes you to roughly 8 millisieverts of radiation, or more than double that dose. And nuclear plant workers – under normal circumstances – are allowed up to 50 millisieverts of radiation exposure each year.
At about 100 millisieverts the risk of developing cancer sometime in the future due to radiation exposure begins to elevate very slightly.
According to the NIH full body exposure to 1000 millisieverts of ionizing radiation results in radiation sickness, while an exposure of 4,000 millisieverts is fatal in about 50% of cases (see Medline article Radiation sickness).
At 6,000 millisieverts (6 Sieverts), death is almost certain.
So, while well above normal, you’d have to be exposed to 3.6 millisieverts a day for nearly a month to reach the first tier of health concern; the 100 millisievert exposure range.
In other words, in the short term this level of exposure is unlikely to pose health risks to residents.
Over time, however, ongoing exposure to this level of radiation would be dangerous.
All of this assumes, of course, that the radiation readings we are getting from the stricken plant and monitoring stations nearby are both comprehensive and accurate.
Two assumptions that are difficult to make right now.
