From previous experiments, did you notice that when you switch on the GM tube, even 
     when there is no radioactive materials nearby, the scaler still records a low count rate! 
     Why is that? It is due to background radiation.

     [Background radiation] comes from several sources:

sources of background radiation

 
   A. Radiation arising from the earth, eg. Radioactive materials from rocks and soil
   B. Radiation from outer space, which is called cosmic radiation or cosmic rays. 
   C. Radiation gases of radon and thorium given off from rocks, soil, building materials
   D. Radiation from our bodies, food and drinks

 
   A. [X-rays]
   B. Fallout from nuclear explosives testing
   C. Radioactive materials released to the environment from nuclear power plants

 
       How do we measure radiation? How much radiation is dangerous to human 
       beings? What are the effects on our bodies? Here are the answers you want to know!

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