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Distinguishing Beta and Gamma
A teacher measured the count rate at different distances for each of two radioactive sources, A and B.
Figure 15 shows the results.
Figure 15 can not be used to determine if Source B emits beta radiation or gamma radiation.
Explain how an absorbing material could be used to show which type of radiation is emitted by Source B.
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Marking points
- 1 Uses aluminium or another appropriately specified beta-absorbing material between source and detector.
- 2 Explains that beta is stopped whereas gamma penetrates, so the count-rate result distinguishes them.
Full-mark answer
Place a sheet of aluminium between Source B and the detector and compare the count rate. If the radiation is stopped, Source B emits beta; if it continues through the aluminium, it emits gamma.
Why this answer loses marks
Put a sheet of metal between the source and detector.
An unspecified metal sheet is not enough. Choose a suitable beta absorber and explain how a stopped or continuing count distinguishes the radiation.