Commonly used gamma-emitting isotopes

Caesium-137 is a radioactive isotope which is formed mianly by nuclear fission (half life is about 27 years). It decays by pure beta decay to a metastable state of Barium-137 which has a half life of minutes, the barium-137m is responsible for all the of gamma emission. The ground state of barium-137 is stable.

The photon energy of the Ba-137m is about 800 KeV. These photons can be used in food irradation, or in cancer treatment. Cs-137 is not widely used for industrial radiography as other isotopes offer higher gamma activitys for a given volume. For instance cobalt-60 and iridium-192 can be made by the neutron irradation of normal non radioactive cobalt and irdium metal.

In addition to their uses in radiography, both cobalt-60 and irridium-192 are used in the radiotheraphy of cancer. The cobalt-60 tends to be used in teletheraphy units while the iridium-192 tends to be used in a different mode of theraphy where a palladium coated iridium/palladium alloy wire is made radioactive by neutron activation. This wire is then inserted into a tummor such as a breast tummor, the tummor is then irradated by the gamma photons from the wire. At the end of the treatment the wire is then removed.