half life

• how is the decay of unstable nuclei measured?

  by using activity and half life
• unit for activity

  becquerel (Bq)

  (where 1 Bq is 1 decay per second)
• why does activity never reach zero?

  there will always be some radioactive material remaining which will decay further
• radioactivity is a ... process


  random
• the radioactivity of a source...

  decreases over time
• half life


  length of time required for half of the radioactive atoms in a sample to decay
• a short half life means...

  the activity falls quickly, because the nuclei are very unstable and rapdily decay
• how are sources with a short half life dangerous?

  because of the high amount of radiation they emit at the start, but they quickly become safe
• a long half life means...

  the activity falls more slowly because most of the nuclei don't decay for a long time, they just sits there, releasing small amounts of radiation for a long time
• how are sources with a long half life dangerous?

  because nearby areas are exposed to radiation for a long time
• half life activity time graph

  
• carbon half life


  5730 years