Cobalt-60 is a radioisotope that is mostly used in the medical field. During the last half of the twentieth century, the use of Cobalt-60 was used widely to kill mutated cells, but modern methods favor X-rays produced from linear accelerators. Its main use was in chemotherapy to kill cancerous cells. Cobalt-60 can be implanted directly on or near mutated cells to help stop the spread of cancer. But mostly, the radiation is given in the form of the 2 gamma rays it produces as external irradiation (sometimes called teletherapy).
The radioactivity of Cobalt-60 is also put to use in sterilizing medical instruments by destroying bacteria and other harmful pathogens.