Radioactive decay and half-life

• What is the purpose of radioactive decay in unstable isotopes?


  To become more stable by emitting radiation
• What do we call materials that contain unstable isotopes?

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


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


  The activity of the sample and its half-life
• 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 are decaying each second?


  600 isotopes
• What is half-life defined as?


  The time taken for the number of radioactive nuclei or activity to halve
• If a sample starts with 1 million unstable nuclei, how many will remain after one half-life?


  500,000 nuclei
• How does the decay process affect the number of unstable particles remaining?


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

  Because there are fewer particles left to decay
• How is the relationship between the number of radioactive nuclei and activity described?


  Fewer radioactive nuclei means lower activity
• How can we visualize the decay process of radioactive materials?


  • By using a graph that plots activity (in becquerels) against time
  • The graph shows a decline in both the number of particles and activity
  • The rate of decline falls, resulting in a curved line
• How do you calculate the half-life from a graph of activity over time?


  By finding the time it takes for the activity to halve
• If the activity drops from 600 to 300 becquerels, how long did it take in the example?


  About two hours
• What does a shorter half-life indicate about a radioactive sample?


  It decays more quickly
• What device is used to measure the activity of radioactive materials?

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


  All decays that reach it each second
• If the half-life of a radioactive source is 40 hours, how many half-lives are there in 5 days?


  Three half-lives
• How many radioactive nuclei remain after three half-lives if starting with 3 million nuclei?


  375,000 nuclei
• What is the process to determine the remaining radioactive nuclei after a certain time period?


  1. Convert the time period into hours.
  2. Divide by the half-life to find the number of half-lives.
  3. Start with the initial number of nuclei.
  4. Halve the number of nuclei for each half-life.