What does the radioactivity of an object do over time?

What is the unit of measuring radioactivity? What does it mean?

What happens when an alpha, beta or gamma ray is given out?

What is half life?

Why do we have to use the measure of half life to measure how quickly radiation falls of?

What is the count-rate?

What does a short half life mean?

What does a long half life mean?

How do you work out the half life of a sample?

How do you work out the half life from a graph?