half life

• What is the half-life of a radioactive isotope?

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

  By observing the decay of nuclei over time
• Why can't scientists predict when a 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
• How can you find the half-life from a graph?

  By observing the time for nuclei to halve
• If you start with 1,000 undecayed nuclei, how many are left after one half-life?

  500 undecayed nuclei
• What happens to the number of undecayed nuclei after another half-life?

  It falls to 250 nuclei
• If a radioactive isotope has a half-life of 15 days, what is the count rate after 45 days?

  25 counts per second
• How many half-lives are in 45 days if the half-life is 15 days?

  3 half-lives
• What is the count rate after the first half-life if the initial rate is 200 counts per second?

  100 counts per second
• What is the count rate after the second half-life if the initial rate is 200 counts per second?

  50 counts per second
• What is the final count rate after three half-lives?

  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 falls to half its initial level
  • Can be determined from decay graphs
• How do you calculate the decrease in count rate after multiple half-lives?

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