Half-Life

• What does half-life refer to in radioactive isotopes?

  Time for half the nuclei to decay
• How can you determine the half-life of a radioactive isotope?

  By measuring the decay of nuclei over time
• Why can't scientists predict when a specific nucleus will decay?

  Because decay is a random process
• What does a long half-life indicate about a radioactive isotope?

  It decays relatively slowly
• What does a short half-life indicate about a radioactive isotope?

  It decays relatively quickly
• What is another definition of half-life?

  Time for count rate to fall to half
• What is the count rate in radioactive decay?

  Number of decays per second recorded
• How can you find the half-life from a graph of undecayed nuclei?

  By identifying when nuclei count halves
• If a sample starts with 1,000 undecayed nuclei, how many are left after one half-life?

  500 undecayed nuclei
• How many half-lives are in 45 days if the half-life is 15 days?

  3 half-lives
• How does the count rate change after each half-life?

  It halves each time
• What is the final count rate after three half-lives from an initial rate of 200 counts per second?

  25 counts per second
• What are the key concepts related to half-life of radioactive isotopes?

  • Half-life is the time for half nuclei to decay
  • Decay is a random process
  • Count rate is the number of decays per second
  • Half-life can be determined from graphs
  • Count rate decreases by half each half-life
• How do you calculate the decrease in count rate after multiple half-lives?

  1. Identify the initial count rate
  2. Determine the number of half-lives
  3. Halve the count rate for each half-life