Cobalt-60

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This article is about the nuclide Cobalt-60. For other uses, see Cobalt-60 (disambiguation).

Cobalt-60 (⁶⁰Co) is a radioactive isotope of cobalt, with a half life of 5.27 years. ⁶⁰Co decays by beta decay to the stable isotope nickel-60 (⁶⁰Ni). In the process of decay, ⁶⁰Co emits one electron with an energy of up to 315 keV and then two gamma rays with energies of 1.17 and 1.33 MeV, respectively.

One gram of ⁶⁰Co contains approximately 50 curies (1.85 terabecquerels) of radioactivity. Held at close range, this amount of ⁶⁰Co would irradiate a person with approximately 0.5 gray of ionizing radiation per minute (also 0.5 sievert per minute, since for this type of ionizing radiation on a whole body, the gray and sievert values are roughly equivalent). A full body dose of approximately 3-4 sieverts will kill 50% of the population in 30 days, and could be accumulated in just a few minutes of exposure to a gram of ⁶⁰Co. ⁶⁰Co has six main beneficial uses:

As a tracer for cobalt in chemical reactions,
Sterilization of medical equipment,
Radiation source for medical radiotherapy,
Radiation source for industrial radiography,
Radioactive source for leveling devices and thickness gauges,
As a radioactive source for food irradiation, and
As a radioactive source for laboratory use.

The creation of ⁶⁰Co is an important step in nucleosynthesis. Without the ⁶⁰Co step, no elements from number 27 through 83 would be created in supernovas. [1] Artificial ⁶⁰Co is created by bombarding a ⁵⁹Co target with a slow neutron source, usually ²⁵²Cf moderated through water to slow the neutrons down, or in a nuclear reactor such as CANDU, where adjuster rods usually made of steel are instead made of Co-59.[2] ⁶⁰Co is also the active isotope in a so-called cobalt bomb, a form of nuclear weapon.

After entering the organism, most of the ⁶⁰Co gets excreted in feces. A small amount is absorbed by liver, kidneys, and bones, where the prolonged exposure to gamma radiation can cause cancer.

Accidental mixing of radioactive sources containing cobalt with metal scrap can result in production of radioactive steel. An example was the radiation accident from December 6, 1983, where a discarded radiation therapy source caused contamination of 5,000 metric tons of steel.