Why does alpha decay occur?

• A. Nucleus is too large to be stable; strong force isn't enough to keep everything together
• B. The nucleus is too light to be stable
• C. The electrons repel its own nucleus causing emission
• D. Thermal agitation causes ejection

Answer: (A)

Heavy nuclei become unstable because the repulsive electric force between protons grows as the nucleus gets larger, while the strong nuclear force that binds nucleons has only a short range. In very heavy nuclei, the strong force can’t perfectly counteract the protons’ electrostatic push, so the system lowers its energy by shedding part of its interior. Emitting an alpha particle—a cluster of two protons and two neutrons—reduces the total charge and mass, moving the daughter nucleus toward a more stable balance of forces. The decay is a quantum tunneling event through the Coulomb barrier, not something driven by temperature or by electrons.