The energy of a radioisotope is a characteristic of the atomic structure of the material.
Consider, for example, Iridium-192 and Cobalt-60, which are two of the more commonindustrial Gamma ray sources. These isotopes emit radiation in two or three discreet
wavelengths. Cobalt-60 will emit 1.17 and 1.33 MeV gamma rays, and Iridium-192 will
emit 0.31, 0.47, and 0.60 MeV gamma rays. It can be seen from these values that the
energy of radiation coming from Co-60 is more than twice the energy of the radiation
coming from the Ir-192. From a radiation safety point of view, this difference in energy
is important because the Co-60 has more material penetrating power and, therefore, is
more dangerous and requires more shielding.