O-LevelPhysicsNuclear Physics5054/12 · Oct/Nov 2025 · Q381 Mark
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?
Aalpha-particles (α-particles), beta-particles (β-particles) and gamma radiation (γ-radiation)
Balpha-particles (α-particles) and beta-particles (β-particles) only
Calpha-particles (α-particles) and gamma radiation (γ-radiation) only
Dbeta-particles (β-particles) and gamma radiation (γ-radiation) only
✓ Correct answer
B: alpha-particles (α-particles) and beta-particles (β-particles) only
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