Radioactive Activity (Strength) and Intensity

Different radioactive materials produce radiation at different rates and at different energy levels. The strength of a source is called its activity, which is defined as the rate at which the isotope decays. Specifically, it is the number of atoms that decay and emit radiation in one second.

The intensity of a radioisotope is related to the level of energy being given off and is a characteristic of the atomic structure of the material. Different elements have different intensities. A number of radioactive sources are used in industrial radiography. Two of the more common industrial Gamma ray sources are Iridium-192 and Cobalt-60. These isotopes emit radiation in two or three discreet wavelengths. Cobalt-60 will emit 1.33 and 1.17 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 intensity (energy) of radiation coming from Co-60 is about twice the intensity of the radiation coming from the Ir-192. From a radiation safety point of view, this difference in intensity is important because the Co-60 has more material penetrating power and, therefore, is more dangerous and requires more shielding.