PHYSICS 2.8

• Half Life


  length of time required for half of the radioactive atoms in a sample to decay by half its mass
• Describe the nature of radioactive decay

  Random and spontaneous
• Half Life graph (decay curve) example

  
• Decay curve x axis

  time
• decay curve y axis


  activity/radiation level/becquerel
• Unit of radiation


  Becquerel (Bq)
• Carbon Dating


  a scientific method used to determine the age of something
• If an isotope has a half-life of 8 days, and radioactivity starts at 100Bq, how long will it take to reach 25Bq?

  16 days (2 half-lives, from 100 to 50Bq, then to 25Bq)
• 3 factors considered when deciding which isotope to use for a medical reason are

  Half-life, penetration, biological effects
• beta emitter uses


  test thickness of paper
• alpha emitter uses


  smoke alarms
• gamma emitter uses


  medical tracers