Physics · Ch 8 — Atomic and Nuclear Physics
Gamma decay
Gamma decay
In both alpha and beta decay, the resulting daughter nucleus is very often left in an excited energy state rather than settling directly into its true ground state; such excited nuclear states typically last only about s before the nucleus drops down to its ground state (or a lower excited state), releasing the excess energy as a highly energetic photon called a gamma ray. Whereas an atom's electronic transitions release photons of only a few eV, gamma-ray photons from nuclear transitions carry energies of order MeV - far more energetic.
The gamma decay process is written
where the asterisk denotes the excited state. Crucially, gamma decay changes neither the mass number nor the atomic number of the nucleus - it is purely a release of excess internal energy, not a transmutation. …
What this figure shows. This figure traces the two competing decay paths of boron-12 (): in the first, it beta-decays directly to ground-state carbon-12 () by emitting an electron carrying the full available energy of 13.4 MeV, while in the second path it beta-decays instead to an excited state of carbon-12 (written ) by emitting a lower-energy electron of 9.0 MeV, and this excited carbon nucleus then immediately emits a 4.4 MeV gamma-ray photon as it drops to the same ground state. The diagram draws these as two parallel vertical energy-level paths side by side so the reader can see directly that gamma decay is the mechanism by which a nucleus left in an excited state after a beta decay sheds its remaining excess energy, and that the electron energy plus the gamma energy …