Question 23
FThe Figure shows how a radioactive source is used to control the thickness of paper made in a factory.
Figure
The source emits beta radiation. The Table shows the count rate recorded by the detector at different times.
Table
| Time in minutes | Count rate in counts per minute |
|---|---|
| 0 | 820 |
| 5 | 818 |
| 10 | 821 |
| 15 | 760 |
| 20 | 819 |
a.[3]
Explain why a beta source is used, rather than an alpha source or a gamma source.
b.[1]
State what happened to the thickness of the paper at 15 minutes.
c.[1]
Describe what the control unit should make the rollers do when the count rate falls.
d.[2]
The source has a half-life of about 29 years.
Suggest why a source with a long half-life is used.