Photodisintegration (also called phototransmutation, or a photonuclear reaction) is a nuclear process in which an atomic nucleus absorbs a high-energy gamma ray, enters an excited state, and immediately decays by emitting a subatomic particle.
The incoming gamma ray effectively knocks one or more neutrons, protons, or an alpha particle out of the nucleus.
Photodisintegration is responsible for the nucleosynthesis of at least some heavy, proton-rich elements via the p-process in supernovae of type Ib, Ic, or II.
[citation needed] A photon carrying 2.22 MeV or more energy can photodisintegrate an atom of deuterium: James Chadwick and Maurice Goldhaber used this reaction to measure the proton-neutron mass difference.
[9] Photofission is a similar but distinct process, in which a nucleus, after absorbing a gamma ray, undergoes nuclear fission (splits into two fragments of nearly equal mass).