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Among the three main types of radioactive radiation, gamma rays have the highest penetrating power. Option C is correct: Gamma rays are electromagnetic radiation with very short wavelength and high energy. They can penetrate several centimetres of lead or metres of concrete. They require thick lead shielding or dense concrete to be stopped. Option A is incorrect: Alpha particles are helium nuclei (2 protons + 2 neutrons) and have the lowest penetrating power. They can be stopped by a sheet of paper or a few centimetres of air. They have the highest ionizing power but lowest penetration. Option B is incorrect: Beta particles are fast-moving electrons or positrons. They have moderate penetrating power and can be stopped by a few millimetres of aluminium. They are more penetrating than alpha but much less than gamma. Option D is partially correct but X-rays are not radioactive decay products; they are produced by electron transitions. Gamma rays are more energetic than typical X-rays. The order is: Alpha < Beta < Gamma.
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