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.
After entering a living mammal (such as a human), most of the 60
Co gets excreted in feces
. A small amount is absorbed by liver
, 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
, 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
incident at the Italian
port of La Spezia
, where a cargo ship from China
was found to contain 30 tons of steel contaminated by 60
In September of 2008, a Chinese-manufactured cheese grater contaminated with 60
Co turned up at a Flint, Michigan recycling plant.
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