GCSE Questions: Radioactivity
Q6.
(a) The diagram shows a radiation detector and counter being used to measure background radiation. The number shows the count ten minutes after the counter was reset to zero.
(i) Name one source of background radiation.
any one from: 
the ground,
the air,
radon (gas),
building materials,
buildings,
rocks / granite,
food,
cosmic rays(or from outer space )
solar rays or the sun (but not sunlight)
nuclear weapons testing,
nuclear power stations / accidents
medical uses
(1 mark)
(ii) Calculate the average background radiation level, in counts per second. Show clearly how you work out your answer.
10 minutes = 600 seconds
1200/600 = 2 counts per second
(2 marks)
(b) The detector and counter are used in an experiment to show that a radioactive source gives out alpha and beta radiation only.
Two different types of absorber are placed one at a time between the detector and the source.
For each absorber, a count is taken over ten minutes and the average number of counts per second worked out.
The results are shown in the table below.
| Absorber used |
Average count per second |
| No absorber |
33 |
| Card 1 mm thick |
20 |
| Metal 3 mm thick |
2 |
Explain how these results show that alpha and beta radiation is being given out, but gamma radiation is not being given out.
The card makes the count drop by 13 counts.
Alpha would be all absorbed by the card , the beta count would be very slightly reduced and the drop in gamma would not be detectable by the card's presence so that shows that there is alpha radiation from the source.
The metal sheet reduces the count to background level, so this shows that the radiation that got through the paper must have been beta as it was absorbed by the metal sheet.
If gamma had been present the count would have been much higher after the metal sheet as it was only 2mm thick.
(3 marks)
(Total 6 marks)
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