When a small radioactive source is placed in a cloud chamber, straight tracks about 4 cm long are observed - AQA - A-Level Physics - Question 18 - 2019 - Paper 2
Question 18
When a small radioactive source is placed in a cloud chamber, straight tracks about 4 cm long are observed. The same source is placed 10 cm from a Geiger tube and a ... show full transcript
Worked Solution & Example Answer:When a small radioactive source is placed in a cloud chamber, straight tracks about 4 cm long are observed - AQA - A-Level Physics - Question 18 - 2019 - Paper 2
Step 1
A α, β and γ
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Answer
When the source is placed in the cloud chamber, the observation of straight tracks indicates that the radiation is likely to be positively charged particles, such as alpha particles, and possibly beta particles as well. The falling count rate after placing aluminium indicates the presence of gamma radiation, which can penetrate certain materials, but less so than alpha and beta particles. Therefore, the source must emit α, β, and γ radiation.
Step 2
B β and γ
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Although this option suggests the presence of beta and gamma radiation, it neglects the alpha particles which contribute significantly to the count observed in the cloud chamber due to their relatively larger mass and charge. Thus, this option is incomplete.
Step 3
C α and γ
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This option implies that only alpha and gamma radiation are emitted. However, it does not account for beta particles, which are also likely emitted given the behavior of the radiation detected.
Step 4
D α and β
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Similar to previous options, this option excludes gamma radiation. Given that the count rate decreases when using aluminium shielding, suggesting the presence of gamma radiation that can penetrate the material.
