Radiation arising from the earth, eg. Radioactive materials from rocks 
    and soil

     All around us, especially in the soil, are natural deposits of uranium, 235U (0.7% abundance)
     and 238U (99.3% abundance) and thorium, 232Th. Uranium and thorium decay into numerous
     other radioactive isotopes before finally decaying into a stable element such as lead.

     By products formed by the decay of radium (radium-226) and thorium are also present in many 
     types of rocks, other building materials and in the soil.


    Cosmic Rays
     High energy electrons, protons, and complex nuclei can be produced in a number of 
     astronomical environments. Such particles travel throughout the universe and are called cosmic
     rays. Some of these particles reach our Earth. These objects hit our atmosphere, and are 
     slowed down. Thus the higher we travel, the more cosmic radiation we experience. When you 
     visit the mountains or take an airplane ride, you will encounter more cosmic radiation than if you 
     stayed at sea level.
cosmic ray diagram
cosmic rays increases with height

    Radiation from gases ( radon and thorium) given off from rocks, soil, building 
    materials

     Radon is produced from naturally occuring uranium-238 in the soil. It is a daughter element 
     of uranium and thorium.
     
     Listed below are a few of common building materials and their estimated levels of 
     uranium, thorium and potassium. 

 

    
Materials

    Uranium ppm
    
 


    
mBq/g

    Thorium ppm
    
 


    
mBq/g

    Potassium ppm
    
 


    
mBq/g

      Granite
    4.7
    63
    2
    8
    4.0
    1184
 

    
Sandstone

    0.45
    6
    1.7
    7
    1.4
    414 
 


    
Cement

    3.4
    56
    5.1
    21
    0.8
    237

    
Limestone concrete

    2.3
    31
    2.1
    8.5
    0.3
    89
 


    
Wood

    ---
    ---
    ---
    --- 
    11.3
    3330

    
Clay Brick

    8.2
    111
    10.8
    44
    2.3
    66
   ppm = parts per million
   Bq = becquerel
 

    Radiation from our bodies, food and drinks
     We ourselves are radioactive. We have radioactive elements (Potassium 40, Carbon 14, 
     Radium 226) in our blood or bones. Potassium 40, the main source of radioactivity in our
     bodies, has a half-life of 1.42 billion years. Our intake of food will sometimes have traces 
     of radioactive elements. Potassium-40 is also found in many foods such as bananas and 
     salt substitutes.
     Here is a table of some of the common foods and their levels of potassium and radium:

    Food
    40K (pCi/kg)
    
 226Ra   
         (pCi/kg)





    Banana
    3,520
    1
 


    Carrot
    3,400
    0.6-2
 


    White Potatoes
    3,400
    1-2.5
 


    Beer
    390
    ---
 


    Red Meat
    3,000
    0.5
 


    Drinking water
    ---
    0-0.17
   Ci = curie

          


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