1.1. A teacher demonstrates an experiment about radioactivity. He demonstrates how different types of radiation can be absorbed.

He puts different barriers between the source and the Geiger-Müller tube. He uses four different radioactive sources A, B, C and D.

Suggest two safety precautions that the teacher should use when demonstrating this experiment.

1 ........................................................................................................

2 ......................................................................................................

1.2. The teacher chooses source A and uses the Geiger-Müller tube to measure the count rate (counts per minute) for different barriers. He repeats the experiment with source B, source C and then source D.

Look at his results.

He also finds that the average count rate with no sources and no barriers is 20.

i) Which source A, B, C or D emits gamma radiation only?

Explain your answer.

Source ............... because ............................................ [2]

ii) Which source A, B, C or D emits alpha radiation only?

Explain your answer.

Source ............... because ............................................ [2]

iii) Which source A, B, C or D could emit both beta and gamma radiation?

Explain your answer.

Source ............... because ............................................ [2]

1.3. The teacher notices that the count rate behind the lead barrier ranges from 20 to 24.

Give two reasons why there are a wide range of results around 22 counts per minute.

1. .....................................................................................................

2. ......................................................................................................

1.4. The teacher decides to repeat the experiment.

This time he records the number of counts for a much longer time interval for each source.

Explain why this is an improvement to the experiment.