1. A radioactive substance has a half-life of 30 minutes.
   What fraction of the atoms will not have decayed after 1 hour?
              click for answer
   
   
2. Another substance has a half-life of 3 hours.
   What fraction of the atoms will have decayed after 6 hours?
              click for answer
   
   
3. A researcher measures 200 counts per minute coming from a radioactive source at midday.
   At 3 o'clock, she finds that this has dropped to 25 counts per minute.
   What is the half-life of the radioactive source?
              click for answer
   

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Created by Andy Darvill, www.darvill.clara.net,Science teacher at Broadoak Community School, Weston-super-Mare, England