half-life

• half-life definition:

  half-life is defined as the time it takes for this activity of a radioactive source to halve, or the time it takes for half the radioactive nuclei to decay.
• the half life for the radioactive source shown on the graph below is 100 days. the time it takes for the activity to halve from 800 to 400 cpm is 100 days, it takes the same time to halve from 400 to 200 cpm and from 200 to 100 cpm. the half-life of a radioactive isotope is always the same.

  
• half life calculation:

  at the start, 100% of the source has not decayed, after 1 half life this will be 50% and after 2 half lives 25%.

  100%->1 half life->50%->2 half lives->25%->3 half lives->12.5%
• example:

  the question below shows an example of using the half-life equation.

  
• uses of radioactive materials:

  radioactive materials have many uses and are determined by their half-life and by the properties of the radiation they release, alpha, beta or gamma.