The activity of all radioactive substances decreases over time. The time it takes for the activity of a material to reduce by half is called the

*half life* of the material. Radioactivity is a random process. We don’t know which atom will be the next one to decay – a bit like we don’t know which piece of popcorn will be the next one to go

pop. However, we do know the time it takes for half of the atoms in a radioisotope to decay – this is our definition of half life.

These notes will show you how to do different types of half life calculations. The maths is straightforward – just make sure you can multiply and divide by 2!

There are 6 different problems to try as you read through the notes, answers are provided on the last page.

*Related*