These gamma rays can be used, for example, in radiotherapy such as for the treatment of cancer, in food irradiation, or in industrial gauges or sensors.
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.
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).
Americium-241 has been used as a source of low energy gamma photons, it has been used in some applications such as portable X-ray fluorescence equipment (XRF) and common household ionizing smoke detectors.
Americium-241 is produced from 239Pu in nuclear reactors through multiple neutron captures and subsequent beta decays with the plutonium-239 itself being produced mostly from neutron capture and subsequent beta decays by 238U (99% of natural uranium and usually roughly 97% of low enriched uranium or MOX fuel).
Radon therapy sits on the edge of radioactive quackery and genuine radiotherapy in part due to the lack of reliable data on the stated health benefits.