Истории и востоковедения

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much background radiation is around, it helps to distinguish between effects 
on normal matter and on the human body. 
The amount of radiation absorbed by non-biological matter is measured 
in grays, a unit equivalent to a joule of energy per kilogram of mass. For 
biological tissue, a dose equivalent is measured in sieverts (Sv) depending 
on the type of radiation involved and how much damage that radiation does 
to the particular cells affected. 
The average amount of radiation received from background sources in 
the UK is around 2–2.5 mSv per year. Because of the preponderance of 
granite, which contains higher than average levels of uranium, in areas such 
as Cornwall or Aberdeenshire it can be twice this level – not high enough to 
cause any concern, but high enough that nuclear facilities can’t be built 
there as the background level already exceeds the maximum allowed 
radiation limit. In some parts of the world, such as northern Iran, the 
background radiation is as high as 50 mSv per year. 
There are a variety of other natural and routine artificial causes of low 
doses of radiation. A dental x-ray will give you a dose of under 1 mSv; a 
full-body CT scan, 10 mSv. As fewer cosmic rays are stopped by the 
atmosphere the higher you go, the crew of a passenger jet flying between 
the US and Japan once a week for a year would receive an additional a dose 
of around 9 mSv. Under normal conditions, the dose limit for workers in the 
nuclear industry is 50 mSv per year. 

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