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specific for ocr gateway additonal science B.

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Question
Answer
where does background radiation come from?   -radioactive substances from rocks (granite) -cosmic rays from space  
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where is most background radiation from?   natural sources e.g. rocks, cosmic rays, air  
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where is the rest of background radiation from?   human activity e.g. food, medical, nucleur power, nucleur weapons testing  
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what are tracers used for?   -to track the dispersal of waste materials -to find leaks or blockages in underground pipes -to track the route of underground pipes  
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what happens when using a tracer to locate a leak in an underground pipe?   -a very small amount of a gamma emitter is put into the pipe -a detector is passed along the ground above the pipe -an increase in activity is detected in the region of the leak -little or no activity is detected after this point  
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what type of rocks contain traces of uranium?   granite  
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what is uranium?   a radioactive material  
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what happens to the uranium isotopes in the rocks?   -they go through a series of decays -this eventually forms a stable isotope of lead  
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how can you find the age of a rock?   by comparing the amounts of uranium and lead present in the rock  
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what is the half life of uranium-238?   4500 million years  
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what is the atomic mass and atomic number of lead?   206 Pb (stable) 82  
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what happens to the proportion of lead as time increases?   also increases  
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how can you tell if a rock is 4500 million years (one half-life) old?   if there are equal quantities of 238 206 U and Pb 92 82  
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what is carbon-14?   a radioactive isotope which is present in all living things  
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how can you find the age?   by measuring the amount of carbon-14 in an archaeology find  
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what happens when an object dies?   no more carbon-14 is produced  
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what happens as carbon-14 decays?   the activity of the sample decreases  
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what leads to a reasonably accurate date?   the ratio of current activity from living matter, to the sample activity  
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