Half- Life

• Half-life


  The time it takes for the number of nuclei of a radioactive isotope in a sample to halve
• Determining half-life


  1. Observe the time it takes for the number of undecayed nuclei to halve

  2. Observe the time it takes for the count rate to halve
• Longer half-life


  Radioactive decay occurs more slowly
• Shorter half-life


  Radioactive decay occurs more rapidly
• Radioactive decay is a random process, so scientists cannot predict when a specific nucleus will decay
• Graphs showing half-life


  • Graph of number of undecayed nuclei over time
  • Graph of count rate over time
• Calculating decrease in count rate after a given number of half-lives


  Count rate halves after each half-life
• A radioactive isotope has a half-life of 15 days and an initial count rate of 200 counts per second. After 45 days, the count rate will be 25 counts per second.