Manmade radioactive sources are produced by introducing an extra neutron to atoms
of the source material. As the material gets rid of the neutron, energy is released in the
form of gamma rays. Two of the most common industrial gamma-ray sources for
industrial radiography are Iridium-192 and Cobalt-60. In comparison to an X-ray
generator, Cobalt-60 produces energies comparable to a 1.25 MV X-ray system and
Iridium-192 to a 460 kV X-ray system. These high energies make it possible to
penetrate thick materials with a relatively short exposure time.