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describe two reasons why an alpha particle is less penetrating than a beta or gamma particle
Alpha particles are energetic (fast) helium nuclei, beta particles are smaller and have half the charge, being energetic electrons (or positrons) only the gamma particles are gamma-ray photons, i.e., they are not massive particles at all, they are a form of electromagnetic radiation, a form more energetic than X-rays.
Source: https://www.quora.com/What-is-the-difference-between-alpha-beta-and-gamma-radiation