Unit for measurement

     Radiation transfers its energy to materials which absorb it. The energy transferred to 
     the materials is called radiation dose, and is expressed in grays. (Gy) 1 Gray is equal
     to one joule of energy transferred to each kg of material.

     Equal exposure to different types of radiation do not however necessarily produce equal 
     biological effects. One gray of alpha radiation, for example, will have a greater effect than
     one gray of beta radiation. Also, some parts of the body are more easily damaged than 
     others. Therefore we use sieverts (Sv) when talking about radiation effects. One sievert of 
     radiation produces a constant biological effect regardless of the type of radiation.

     Since 1 Sv is a large dose, therefore smaller quantities are expressed in 'millisieverts' 
     (one thousandth) or 'microsieverts' (one millionth) of a sievert.


    Dose from background radiation
    On average, our radiation exposure due to all natural sources amounts to about 2.2  mSv a 
    year-though this figure can vary, depending on the geographical location  by several hundred 
    percent.

    The dose we received from background radiation are as follows:

      Dose (milliSv/year)

    Naturally Occurring

      cosmic rays

    
0.32

    
  internal (from air, food, and water)

    
1.30

    
 external (from soil and rocks)

    
0.35

    
                 Total

    
0.97

    Artificially Created

    
  medical exposure

    
0.50

    
     fallout from nuclear testing	

    
0.04

    
                 Total

    
0.54

      Do you want to calculate your annual radiation dose? CLICK HERE!

    How much radiation is dangerous? 

     The following table gives an indication of the likely effects and implications of a range
     of radiation doses and dose rates to the whole body:

Effective dose

       Large exposure to radiation may also results in:

• Leukaemia
• Genetic mutation, if reproductive cells are damaged
• Cancer, especially thyroid cancer
• Thyroid enlargement and nodules (usually occurs among children, because of their larger absorbed thyroid dose longer life-span, and increased sensitivity relative to adults
• Thermal burns
• Radiation-induced damage to skin and mucous membranes
• Permanent impaired fertility in males
• Eye problems like cataracts
• Cardiovascular and gastrointestinal problems

       If pregnant women are exposed to too much radiation, the foetuses may be seriously 
       affected since radiation cause drastic damage on actively dividing cells. Moreover, it 
       has been found that foetuses are especially sensitive to certain types of radiation 
       during the first 2 to 3 months after conception. 

       The following table shows how are the foetuses affected by radiation.

    
Effect

    
Number Occurring

    from Natural Causes

    

    
Risk Factor

    
Excess Occurrences

    from Risk Factor

    

    Cancer death in children

    1.4 per thousand

    

      
Childhood Cancer      Radiation
      dose of       1000 [millirems]      received before birth
      
Abnormalities     Radiation
      dose of 1000 [millirads] received during      specific periods
      after  conception
    

    
0.6 per thousand

    Small head size

    40 per thousand

    4-7 weeks after conception

    5 per thousand

    Small head size

    40 per thousand

    8-11 weeks after conception

    9 per thousand
 

    Mental retardation

    4 per thousand

    
Radiation dose of 1000 
millirads received 8 to 15 
weeks after conception

    4 per thousand

    A bone marrow transplant or a blood transfusion could be used to treat patients, who 
    exposed to excessive radiation. However, people who received fatal radiation doses 
    could not be cured effectively by any medical treatments at present.

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