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. 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. ⁶⁰Co is also the active isotope in a so-called cobalt bomb, a theoretically feasible but extremely "dirty" form of nuclear weapon whereby a tamper of ⁵⁹Co is irradiated by neutron radiation from the fission process and transmuted to ⁶⁰Co.

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. Another example of Co-60 contamination is the March 1, 2008 incident at the Italian port of La Spezia, where a cargo ship from China was found to contain 30 tons of steel contaminated by ⁶⁰Co In September of 2008, a Chinese-manufactured cheese grater contaminated with ⁶⁰Co turned up at a Flint, Michigan recycling plant.

External links

• Cobalt-60, Environmental Protection Agency.
• National Pollutant Inventory - Cobalt fact sheet
• Cobalt-60, Oak Ridge National Laboratory.
• Cobalt-60, Centers for Disease Control and Prevention.
• NLM Hazardous Substances Databank – Cobalt, Radioactive
• Beta decay of Cobalt-60, HyperPhysics, Georgia State University.

Dr. Henry Kelly. Cobalt-60 as a Dirty Bomb, Federation of American Scientists, March 6, 2002.

Sequestrato acciaio radioattivo contaminato da cobalto, ItalyGlobalNation

Italians seize 30 tons of radioactive steel, USA Today