“Radiation can be described as small packets of energy. When they hit the genetic code, the molecule of DNA, they can break, split.”
Wendla Paile, Chief Radiologist, Radiation and Nuclear Safety Authority, Finland (source: Into Eternity).
Units of measurement of radioactivity
The average value of irradiation from natural radionuclides on the world’s population is around 57 nGy/h (outdoor). This value can be much higher in some areas of the world, for example 20,400 nGy/h in the Nile Delta. The average Italian value of irradiation inside buildings (indoor) is 150 nGy/h.
To measure the biological effects, it multiplies the Gray to a factor that depends by the radiation, and you get the Sievert (Sv), a measure of the biological effect due to the dose of radiation absorbed.
Mild effects of a radiative intoxication appear between 0.5 Sv (500 mSv) and 1 Sv (1000 mSv). It have more serious effects above 1 Sv.
milliSievert (1 mSv = 1000 uSv)
Sievert (1 Sv = 1000 mSv)
Dose = total amount of radioactivity absorbed by the body over a certain period.
Dose rate = the amount of radioactivity absorbed per hour, expressed in
micro Sievert per hour (µSv/h)
milli Sievert per hour (mSv/h =1000 µSv/h)
See the Table of doses of radiation (pdf).
Comparison of doses from sources of exposure (Source: Health Protection Agency)
- Dental X-ray: 0.005 mSv
- 135g bag of Brazil nuts: 0.01 mSv
- Chest X-ray: 0.02 mSv
- Transatlantic flight: 0.07 mSv
- Nuclear power station worker average annual occupational exposure: 0.2 mSv
- UK annual average radon dose: 1 mSv
- CT scan of the head: 1.4 mSv
- UK average annual radiation dose: 2.7 mSv
- USA average annual radiation dose: 6.2 mSv
- CT scan of the chest: 6.6 mSv
- Average annual radon dose to people in Cornwall: 7.8 mSv
- Whole body CT scan: 10 mSv
- Annual exposure limit for nuclear industry employees: 20 mSv
- Level at which changes in blood cells can be readily observed: 100 mSv
- Acute radiation effects including nausea and a reduction in white blood cell count: 1000 mSv
- Dose of radiation which would kill about half of those receiving it in a month: 5000 mSv
This Greenpeace briefing to provide analysis and advice of the risks and potential health impacts following releases of radioactivity from Japan’s Fukushima 1/Daiichi nuclear power plant, which was damaged by the March 11th earthquake and tsunami.
Rianne Teule, Greenpeace Energy Campaigner, March 19, 2011, updated 23 March 2011.
Jeremy Singer-Vine, Slate, March 17, 2011.
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