Half life

• What are the two terms discussed in the video?

  Activity and half-life
• What is the purpose of radioactive decay?

  To become more stable
• What do we call materials that emit radiation?

  Radioactive materials
• How can we predict decay in a large sample of isotopes?

  By measuring the overall activity
• How is activity measured?

  In becquerels
• What does one becquerel represent?

  One decay per second
• What is half-life defined as?

  Time for radioactive nuclei to halve
• How does half-life relate to activity?

  Both halve at the same time
• What happens to the number of unstable particles over time?

  It decreases as they decay
• Why does the activity of a sample decrease over time?

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

  • Decline in number of particles
  • Decline in activity
  • Curved decline, not linear
• How do you calculate half-life from a graph?

  Find time for activity to halve
• What is the half-life if activity drops from 600 to 300 in two hours?

  Two hours
• What is the half-life of the second radioactive sample discussed?

  One hour
• 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
• How do you find the remaining nuclei after five days with a half-life of 40 hours?

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

  375,000 nuclei
• What are the steps to calculate remaining nuclei after multiple half-lives?

  1. Convert total time to hours
  2. Divide by half-life to find half-lives
  3. Half the initial amount for each half-life