promoting the sustainable and responsible use of cobalt in all forms

Radioactivity

Do radioactive forms of cobalt exist?

Yes, but radioactive forms of cobalt do not occur naturally. There are four man-made radioisotopes of cobalt- 56Co, 57Co, 58Co and 60Co.

An isotope is a form of an element that differs by the number of neutrons present in the nucleus, thereby differing in mass number but not atomic number (number of protons).

The cobalt isotope found in nature (i.e. 59Co) is non-radioactive, and is an element found in rocks, soil, water, plants, animals and humans.

The table below lists the properties of the naturally-occurring form of Co (59Co) followed by the four synthetic radioactive isotopes (56Co, 57Co, 58Co and 60Co):

Nuclide 59Co 56Co 57Co 58Co 60Co
Atomic Mass 58.933 55.940 56.936 57.936 59.934
Natural Abundance 100% 0% 0% 0% 0%
Half Life Stable, non-radioactive 77 days 270 days 71.3 days 5.26 years

The cobalt radioisotopes are produced in either a particle accelerator (for commercial or healthcare uses) or indirectly as a by-product of nuclear reactors, when structural materials (e.g. steel) are exposed to neutron radiation.


Cobalt-60

Cobalt-60 (60Co) has been used for radiotherapy cancer treatment, food irradiation and industrial applications.

As cobalt-60 decays into a stable nickel-60 isotope, two wavelengths of high-energy gamma-rays are emitted (1.17 and 1.33 MeV- average of 1.25 MeV used).

Cobalt-60 has been used in the treatment of cancer for over 60 years[1], within an instrument known as the Gamma Knife. The Gamma Knife was invented in 1967 and is used to treat brain tumours and vascular malformations. The gamma rays emitted by cobalt-60 are harnessed by the radiotherapy instrument which is highly effective in precisely delivering a high dose of radiation to the tumour area and therefore preserving surrounding healthy tissue[2].

Due to cost effectiveness, reliability and ease of use/maintenance, the use of cobalt-60 in radiotherapy treatment still accounts for approximately 70% of world-wide cancer radiation-treatment cases[3].

70% of cancer sufferers who require radiotherapy, receive radiation from cobalt-60.

Large sources of cobalt-60 are used in the sterilisation of spices and certain foods by a process often referred to as ‘cold pasteurisation’. The gamma associated radiation emitted kills bacteria and other pathogens, without altering the food product or retaining any radioactivity after treatment.

Cobalt-60 is used in common industrial applications, such as levelling devices and thickness gauges. In particular, this isotope is used in industrial radiography where radiation is used for non-destructive detection of structural flaws in metal parts.

An example of gamma knife technology
The Gamma Knife was invented in 1967 and is used to treat brain tumours and vascular malformations.


Cobalt-57 and Cobalt-58

Another radioactive isotope of cobalt, 57Co, has been used in the radioactive form of Vitamin B12 for the Schilling Test.

This is a test used to determine whether a patient is absorbing Vitamin B12 normally. The Schilling test is primarily used to test for a specific type of anaemia (i.e. a decrease in red blood cells resulting from improper absorption of Vitamin B12 from the intestinal tract)[4]. The test involves ingestion of radioactive Vitamin B12 alongside intravenous injections of non-radioactive Vitamin B12 in order to evaluate the cause of the abnormal absorption. Cobalt-58 has also been used in the Schilling Test when evaluation of the percentages of 57Co vs 58Co are needed[5].


Cobalt-56

There are no uses noted for cobalt-56 in the literature.

However, Russian astrophysicists discovered cobalt-56 was transiently present in a supernova explosion[6]. Scientists were able to detect 56Co using an INTEGRAL gamma-ray orbital telescope, as radioactive nickel-56 decayed, cobalt-56 was formed which then decayed into iron-56.


DISCLAIMER

This summary is intended to provide general information about the topic under consideration. It does not constitute a complete or comprehensive analysis, and reflects the state of knowledge and information at the time of its preparation. This summary should not be relied upon to treat or address health, environmental, or other conditions.



[1] http://www.lhsc.on.ca
[2] The National Centre for Stereotactic Radiosurgery, NHS Sheffield Teaching Hospitals http://www.gammaknife.org.uk/
[3] http://www.lhsc.on.ca
[4] https://www.nlm.nih.gov
[5] Laboratory Assessment of Nutritional Status: Bridging Theory and Practice. Mary Litchford 2011 ISBN-13:978-1-8809-8951-7
[6] http://www.nature.com