GCSE Questions: Radioactivity


Smoke alarms contain an alpha radiation source and a radiation detector.

The diagram below shows part of the inside of a smoke alarm.

(a) The smoke alarm stays off while alpha radiation reaches the detector. Why does the alarm switch on when smoke particles enter the plastic casing?

[1 mark]

(b) Why is it safe to use a source of alpha radiation in a house?

[1 mark]

(c) The smoke alarm would not work with a radiation source that emits beta or gamma radiation. Explain why.

[2 marks]

(d) The graph below shows how the count rate detected from the radiation source in the smoke alarm changes with time.

The smoke alarm switches on when the count rate falls to 80 counts per second.

Explain why the radiation source inside the smoke alarm should have a long half-life.

[2 marks]

(e) The photo shows a patient who has been injected with a radioactive source for medical diagnosis.

Explain the ideal properties of a radioactive source for use in medical diagnosis.

[4 marks]

[Total: 10 marks]