Gamma decay
The radioactive decay of an excited nucleus by emitting a high-energy photon (gamma ray: γ) without changing the number of protons or neutrons. Gamma decay represents the nucleus transitioning from an excited state to a lower-energy state. Gamma rays are highly penetrating, requiring lead or concrete shielding. Gamma emission often follows alpha or beta decay when the daughter nucleus is left in an excited state.
Real World
Technetium-99m, used in millions of NHS medical scans annually, emits gamma rays after being injected into patients — allowing doctors to image organs without altering the nucleus's proton or neutron count.
Exam Focus
State that gamma emission changes neither mass number nor atomic number; many students incorrectly write a change in proton number.
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