This question is about radioactivity.

1. (a)A teacher sets up a Geiger-Müller detector near a radioactive source, as shown in the diagram. [Figure 4] Explain why it is important to measure background radiation and how this is done.[2]
2. (b)(i)A radioactive source has a half-life of 2.0 minutes. The initial count rate from the source is 800 counts per second. Calculate the time taken for the count rate to fall to 200 counts per second.[2]
3. (b)(ii)State the unit for activity.[1]
4. (b)(iii)Explain why nuclear waste from power stations has to be stored carefully for a long time.[3]
5. (c)Describe the difference between nuclear fission and nuclear fusion.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.