Some radionuclides, such as cobalt-60 and iridium-192, are made by the neutron irradiation of normal non-radioactive cobalt and iridium metal in a nuclear reactor, creating radioactive nuclides of these elements which contain extra neutrons, compared to the original stable nuclides.
In addition to their uses in radiography, both cobalt-60 () and iridium-192 () are used in the radiotherapy of cancer. Cobalt-60 tends to be used in teletherapy units as a higher photon energy alternative to caesium-137, while iridium-192 tends to be used in a different mode of therapy, internal radiotherapy or brachytherapy.  The iridium wires for brachytherapy are a palladium-coated iridium/palladium alloy wire made radioactive by neutron activation. This wire is then inserted into a tumor such as a breast tumor, and the tumor is irradiated by gamma ray photons from the wire. At the end of the treatment the wire is removed.
A rare but notable gamma source is sodium-24; this has a fairly short half-life of 15 hours, but it emits photons with very high energies (>2 MeV). It could be used for radiography of thick steel objects if the radiography occurred close to the point of production. Similarly to  and , it is formed by the neutron activation of the commonly found stable isotope.