A Geiger counter is placed near a radioactive source and different materials are placed between the source and the Geiger counter - AQA - A-Level Physics - Question 27 - 2017 - Paper 2

To determine the type of radiation emitted by the source, we analyze the count rates provided in the table:

• None: A count rate of 1000 s⁻¹ indicates that all radiation reaches the Geiger counter, implying that the source emits radiation that can pass through air.

• Paper: The count remains at 1000 s⁻¹, indicating that the radiation is not stopped by paper. This suggests that the radiation could be alpha (α) or gamma (γ) as alpha particles are not significantly attenuated by paper.

• Aluminium foil: The count rate drops to 250 s⁻¹, suggesting that some radiation is absorbed. This indicates that the source emits some beta (β) radiation since beta particles can partially be stopped by a few millimeters of aluminium.

• Thick steel: The count drops to 50 s⁻¹, indicating that gamma radiation is still present, but both alpha and beta would be significantly reduced by thick steel.

Given this analysis, the radiation emitted by the source must include alpha and beta radiation since they can penetrate only to a certain degree, while gamma radiation is not stopped by any material listed.