photodisintegration

Photodisintegration, also called a photonuclear reaction, is the process by which a nucleus absorbs a high-energy photon, typically a gamma ray, and emits one or more nucleons or light clusters. The result is a different (usually lighter) nucleus. The phenomenon is studied in nuclear physics and has relevance for astrophysics, cosmochemistry, and nuclear engineering.

Mechanism and energy dependence: The absorbed energy excites the nucleus to high-lying levels, most prominently the giant dipole resonance, which favors single-nucleon emission such as (gamma, n), (gamma, p), or (gamma, alpha). At higher photon energies, multi-particle emissions like (gamma, 2n) or (gamma, np) become possible. The threshold for photodisintegration is set by the binding energy of the emitted particles; for deuterium it is about 2.226 MeV, while for many heavier nuclei it lies in the few-MeV to tens-of-MeV range. The cross section generally peaks in the giant dipole region (roughly 10–20 MeV for many nuclei) and then decreases with energy.

Common reaction channels include gamma+n, gamma+p, and gamma+alpha, producing lighter nuclei that may be stable or radioactive. Photodisintegration is one route by which gamma radiation can alter isotopic abundances in astrophysical environments and can compete with other photon-absorption processes under certain conditions.

In laboratories, photonuclear reactions are studied using tagged photon beams produced by bremsstrahlung or laser Compton scattering. Measured cross sections and reaction products inform models of nuclear structure, reaction mechanisms, and astrophysical reaction networks, including those relevant to the p-process and explosive nucleosynthesis.