Physics · Oct / Nov 2025 · Paper 12 · Question 38

A radioactive source is placed 2.0 cm away from a Geiger–Müller (G.M.) tube that is connected to a counter. A sheet of paper is placed between the source and the G.M. tube. The count rate measured by the counter decreases to a value greater than the background radiation count rate. A sheet of aluminium replaces the paper and the count rate decreases to the background radiation count rate. What is the radiation emitted by the source?

1. Aalpha-particles (α-particles), beta-particles (β-particles) and gamma radiation (γ-radiation)
2. Balpha-particles (α-particles) and beta-particles (β-particles) only
3. Calpha-particles (α-particles) and gamma radiation (γ-radiation) only
4. Dbeta-particles (β-particles) and gamma radiation (γ-radiation) only

As printed in the paper