Photodisintegration (also called
phototransmutation) is a physical process in which an extremely high energy
gamma ray is absorbed by an
atomic nucleus and causes it to enter an excited state, which immediately decays by emitting a subatomic particle. A single
proton,
neutron or
alpha particle is effectively knocked out of the nucleus by the incoming gamma ray. Photodisintegration is
endothermic (energy absorbing) for atomic nuclei lighter than
iron and sometimes
exothermic (energy releasing) for atomic nuclei heavier than
iron. Photodisintegration is responsible for the
nucleosynthesis of at least some heavy, proton rich elements via
p-process which takes place in
supernovae.