Radioactive Decay & Half Life

• What are the two terms discussed in the video?

  Activity and half-life
• What happens to unstable isotopes to become more stable?

  They decay by emitting radiation
• What do we call materials that emit radiation?

  Radioactive materials
• Why can't we predict when a single radioactive isotope will decay?

  Because the decay process is random
• What can we determine from a large sample of radioactive isotopes?

  Activity and half-life of the sample
• How is activity measured?

  In becquerels
• What does one becquerel represent?

  One decay per second
• If a sample has an activity of 600 becquerels, how many isotopes decay each second?


  600 isotopes decay each second
• What is half-life defined as?

  The time for radioactive nuclei to halve
• How can half-life be defined in terms of activity?

  As the time taken for activity to halve
• How does the decay process affect the number of unstable particles over time?

  The number of unstable particles decreases
• Why does the overall rate of decay decrease over time?

  Fewer particles remain to decay
• What does a graph of activity against time show?

  Activity declines and the rate of decline falls
• How do you calculate half-life from a graph?

  Find the time for activity to halve
• What is the half-life of the sample in the example?

  Two hours
• How many half-lives occur in five days if the half-life is 40 hours?

  Three half-lives
• If you start with 3 million radioactive nuclei, how many remain after three half-lives?

  375,000 nuclei remain
• What device is used to find the activity of a radioactive sample?

  Geiger-Muller tube
• What does a Geiger-Muller tube record?

  Decays that reach it each second
• What is the count rate used for?

  To estimate the activity of the sample
• What are the key concepts of radioactive decay and half-life?

  • Radioactive isotopes decay randomly
  • Activity is the rate of decay measured in becquerels
  • Half-life is the time for nuclei or activity to halve
  • Fewer unstable nuclei lead to decreased activity
  • Graphs show declining activity over time
• How do you calculate the remaining radioactive nuclei after multiple half-lives?

  1. Determine total time in hours
  2. Divide by half-life to find number of half-lives
  3. Start with initial nuclei count
  4. Halve the count for each half-life