Photofission is a process in which a nucleus, after absorbing a gamma ray, undergoes nuclear fission and splits into two or more fragments.
The reaction was discovered in 1940 by a small team of engineers and scientists operating the Westinghouse Atom Smasher at the company's Research Laboratories in Forest Hills, Pennsylvania.
[1] They used a 5 MeV proton beam to bombard fluorine and generate high-energy photons, which then irradiated samples of uranium and thorium.
[2] Gamma radiation of modest energies, in the low tens of MeV, can induce fission in traditionally fissile elements such as the actinides thorium, uranium,[3] plutonium, and neptunium.
[6] Photodisintegration (also called phototransmutation) is a similar but different physical process, in which an extremely high energy gamma ray interacts with an atomic nucleus and causes it to enter an excited state, which immediately decays by emitting a subatomic particle.