Half-lives and Radioactive Decay

• 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 is the activity of a sample?

  The overall rate of decay of isotopes
• 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
• If a sample starts with 1 million unstable nuclei, how many will remain after one half-life?

  500,000 unstable nuclei
• What happens to the number of unstable particles as time goes on?

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

  Fewer particles are left to decay
• How does the graph of activity against time appear?

  It is curved rather than a straight line
• How do you calculate half-life from a graph?

  Find the time for activity to halve
• What device is used to measure activity in real life?

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

  Decays that reach it each second
• If the half-life of a radioactive source is 40 hours, how many half-lives are in 120 hours?

  Three half-lives
• How many radioactive nuclei remain after three half-lives from 3 million?

  375,000 radioactive nuclei
• What are the key concepts of radioactive decay discussed in the video?

  • Activity: overall decay rate measured in becquerels
  • Half-life: time for nuclei or activity to halve
  • Random decay process of isotopes
  • Decrease in unstable particles over time
  • Use of Geiger-Muller tube for measuring activity
• How does the decay process of radioactive isotopes affect activity over time?

  • Decay process is random
  • Fewer unstable particles lead to lower activity
  • Activity decreases as time progresses
  • Graph of activity vs. time is curved
• How do you determine the remaining radioactive nuclei after multiple half-lives?

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