Exam-style question
Try this first
In an absorption experiment, a thin foil of aluminium is placed between a gamma source and a detector. Which statement best explains why the detector count rate changes only slightly with increasing foil thickness?.
- A.Gamma rays are absorbed by the foil, so the count rate drops sharply.
- B.Gamma rays are reflected by the foil, reducing the count rate.
- C.Gamma rays pass through the foil with little interaction, so the count rate is almost unchanged.
- D.Gamma rays are converted to beta radiation by the foil, altering the count rate.
Model answer
What a good answer should say
- Gamma rays pass through the foil with little interaction, so the count rate is almost unchanged.
Explanation
Why this works
Gamma radiation interacts weakly with matter; a thin aluminium foil provides negligible attenuation. Therefore, the detector records almost the same count rate regardless of the foil thickness, illustrating the high penetration ability of gamma rays.
Common mistake
No common mistake is linked to this question yet.