cobalt-60

cobalt-60 is a synthetic radioactive isotope of the element cobalt. It is produced artificially in nuclear reactors and is a potent source of gamma rays. Due to its predictable decay and high-energy emissions, it has become one of the most important isotopes for applications in medicine, industry, and scientific research.

Properties

Cobalt-60 decays to stable nickel-60 via beta decay, emitting a beta particle and subsequently two high-energy gamma ray photons with energies of 1.17 and 1.33 megaelectronvolts. Its half-life of approximately 5.27 years makes it useful for long-term applications while requiring eventual source replacement. The isotope's consistent and penetrating radiation profile is characterized by its decay chain and has been precisely measured by institutions like the National Institute of Standards and Technology.

Production

The primary method for production involves irradiating natural cobalt-59 with thermal neutrons in a nuclear reactor, such as those operated by Atomic Energy of Canada Limited or the Bhabha Atomic Research Centre. The neutron capture reaction transforms the stable isotope into the radioactive form. Specialized production facilities, including the NRU reactor at Chalk River Laboratories, have historically been key suppliers. The processed metal is then encapsulated in stainless steel or other metals to create sealed sources for safe handling and transport.

Applications

In medicine, it is a cornerstone of radiation therapy, with machines like the Gamma Knife and Theratron using it to treat cancer and other conditions. Its gamma rays are also employed in blood irradiation to prevent transfusion-associated graft-versus-host disease. Industrially, it is used in radiography to inspect welds and castings, and in food irradiation facilities approved by the Food and Drug Administration to sterilize spices and certain produce. It serves as a calibration standard for radiation dosimeters and has been used in industrial radiography units worldwide.

Health and safety

As a significant radiation hazard, exposure can cause acute radiation syndrome and increase cancer risk, governed by regulations from bodies like the International Atomic Energy Agency and the Nuclear Regulatory Commission. Major incidents, such as the Goiânia accident in Brazil, underscore the dangers of orphaned sources. Safe handling requires lead or depleted uranium shielding, strict security protocols to prevent use in radiological weapons, and robust disposal plans, often involving long-term storage at facilities like the Waste Isolation Pilot Plant.

History

The isotope was first discovered in 1939 by John Livingood and Glenn T. Seaborg at the University of California, Berkeley using the cyclotron. Its potential for teletherapy was pioneered in the 1950s, notably by Canadian physicist Harold Johns, leading to the first cancer treatment with a cobalt bomb in London, Ontario. The CANDU reactor design facilitated large-scale production. Its role expanded during the Cold War for industrial radiography and food irradiation, with significant technological development supported by the Atomic Energy Commission.

Category:Isotopes of cobalt Category:Gamma ray sources Category:Industrial radiography