(3) Cobalt-60 is a synthetic radioactive isotope of cobalt with a half-life of 5.2714 years. It is produced artificially in nuclear reactors. Deliberate industrial production depends on neutron activation of bulk samples of the monoisotopic and mononuclidic cobalt isotope Cobalt therapy or cobalt-60 therapy is the medical use of gamma rays from the radioisotope cobalt-60 to treat conditions such as cancer. Beginning in the 1950s cobalt-60 was widely used in external beam radiotherapy(teletherapy) machines, which produced a beam of gamma rays which was directed into the patient’s body to kill tumour tissue.