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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
Identify the Properties of Radiation
Answer
Radioactive sources can emit different types of radiation such as alpha (α), beta (β), and gamma (γ). Each type has distinct properties that affect their interaction with materials.
Alpha particles are heavy and can be stopped by a sheet of paper or a few centimeters of air. Beta particles are lighter, capable of penetrating more but can be blocked by materials like plastic or aluminum. Gamma rays are high-energy photons that are highly penetrating and require dense materials like lead for shielding.
Step 2
Analyze the Cloud Chamber Observation
Answer
The observation of straight tracks about 4 cm long suggests the presence of charged particles, which are typical of alpha or beta radiation. Since alpha particles are heavy and produce shorter tracks due to their mass, it indicates that both alpha and beta radiations could be involved.
Step 3
Evaluate the Geiger Tube Measurement
Answer
When the source was moved 10 cm away from the Geiger tube, the count rate was detected, indicating that the emitted radiation can reach this distance. After placing a 5 mm thick aluminum sheet, the count rate dropped to background levels, suggesting that beta particles (which can penetrate aluminum) and possibly gamma rays (which can penetrate a range of materials) are present.
Step 4
Conclusion on Types of Radiation
Answer
Considering the observations from both the cloud chamber and Geiger tube, the source emits alpha and beta radiation. The presence of aluminum decreasing the count rate supports that beta radiation is likely emitted since alpha particles could be absorbed by a paper and not penetrate through a thicker material like aluminum.
Step 5