Cobalt-60

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  Cobalt-60 (⁶⁰Co) is a radioactive isotope of cobalt, with a half life of 5.27 years. ⁶⁰Co decays by negative 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. With a point source at a range of 1 m, this amount of ⁶⁰Co would give a person a radiation dose of 0.5 sievert (50 rem) per hour. ⁶⁰Co has seven 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 blood 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.

Excretion

After entering a living mammal (such as a human), 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.

Incidents

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 in Mexico, where a discarded radiation therapy source caused contamination of 5,000 metric tons of steel.