Homework - Half-life calculations

1. In the following questions work out how many half lives are shown and calculate the half-life.

   Example: Initial activity 600 MBq, final activity 75 MBq after 60 minutes. 600 decays to 300 decays to 150 decays to 75. 3 half-lives are shown, so:

   3t_1/2 = 60 min

   Answer: The half-life is t_1/2 = 20 min

   1. Initial activity 1800 MBq, final activity 225 MBq after 3 years.
   2. Initial activity 36 000 kBq, final activity 2 250 kBq after 40 000 years.
   3. Initial activity 320 MBq, final activity 0.625 MBq after 18.9 seconds.


2. In the following questions, work out the final activity after the given time:
   1. Initial activity 100 MBq, half-life 4 weeks, final activity after 16 weeks?
   2. Initial activity 360 MBq, half-life 0.6 min, final activity after 54 minutes?


3. In the following questions, work out the initial activity given the final activity and number of half-lives over which measurements were made:
   1. Final activity 10 MBq after 4 half-lives.
   2. Final activity 2 MBq after 8 half-lives.