Cobalt-60
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Cobalt-60 (60Co) is a
synthetic Synthetic things are composed of multiple parts, often with the implication that they are artificial. In particular, 'synthetic' may refer to: Science * Synthetic chemical or compound, produced by the process of chemical synthesis * Synthetic o ...
radioactive isotope of cobalt with a half-life of 5.2713 years. It is produced artificially in
nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...
s. Deliberate industrial production depends on neutron activation of bulk samples of the monoisotopic and mononuclidic cobalt
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass number ...
. (PDF also located a
Canadian Nuclear FAQ
Measurable quantities are also produced as a by-product of typical nuclear power plant operation and may be detected externally when leaks occur. In the latter case (in the absence of added
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, ...
) the incidentally produced is largely the result of multiple stages of neutron activation of iron isotopes in the reactor's steel structures via the creation of its precursor. The simplest case of the latter would result from the activation of . undergoes beta decay to the stable isotope nickel-60 (). The activated nickel nucleus emits two
gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nucleus, atomic nuclei. It consists of the shortest wavelength electromagnetic wav ...
s with energies of 1.17 and 1.33 MeV, hence the overall equation of the nuclear reaction (activation and decay) is: + n → → + e + + gamma rays.


Activity

Corresponding to its half-life, the radioactive activity of one
gram The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to ...
of is . The ''absorbed dose constant'' is related to the decay energy and time. For it is equal to 0.35  mSv/(GBq h) at one meter from the source. This allows calculation of the equivalent dose, which depends on distance and activity. For example, a source with an activity of 2.8 GBq, which is equivalent to 60 μg of pure , generates a dose of 1 mSv at one meter distance within one hour. The swallowing of reduces the distance to a few millimeters, and the same dose is achieved within seconds. Test sources, such as those used for school experiments, have an activity of <100 kBq. Devices for nondestructive material testing use sources with activities of 1 TBq and more. The high γ-energies result in a significant mass difference between and of 0.003  u. This amounts to nearly 20 watts per gram, nearly 30 times larger than that of .


Decay

The diagram shows a (simplified) decay scheme of and . The main β-decay transitions are shown. The probability for population of the middle energy level of 2.1 MeV by β-decay is 0.0022%, with a maximum energy of 665.26 keV. Energy transfers between the three levels generate six different gamma-ray frequencies. In the diagram the two important ones are marked.
Internal conversion Internal conversion is a non-radioactive, atomic decay process where an excited nucleus interacts electromagnetically with one of the orbital electrons of an atom. This causes the electron to be emitted (ejected) from the atom. Thus, in interna ...
energies are well below the main energy levels. is a
nuclear isomer A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy higher energy levels than in the ground state of the same nucleus. "Metastable" describes nuclei whose excited states have ...
of with a half-life of 10.467 minutes. It decays by internal transition to , emitting 58.6 keV gamma rays, or with a low probability (0.22%) by β-decay into .


Applications

The main advantage of is that it is a high-intensity gamma-ray emitter with a relatively long half-life, 5.27 years, compared to other gamma ray sources of similar intensity. The β-decay energy is low and easily shielded; however, the gamma-ray emission lines have energies around 1.3 MeV, and are highly penetrating. The physical properties of cobalt such as resistance to bulk oxidation and low solubility in water give some advantages in safety in the case of a containment breach over some other gamma sources such as caesium-137. The main uses for are: * As a tracer for cobalt in chemical reactions * Sterilization of medical equipment. * Radiation source for medical
radiotherapy Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Ra ...
. Cobalt therapy, using beams of gamma rays from teletherapy machines to treat cancer. * Radiation source for industrial radiography. * Radiation source for leveling devices and thickness gauges. * Radiation source for pest insect sterilization. * As a radiation source for food irradiation and blood irradiation. Cobalt has been discussed as a " salting" element to add to
nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...
s, to produce a cobalt bomb, an extremely "dirty" weapon which would contaminate large areas with nuclear fallout, rendering them uninhabitable. In one hypothetical design, the
tamper Tamper may refer to: *Tamper, to use a tamp, a tool for material compaction *Tamper, a pipe tool component * Tamper (nuclear weapons), a layer of dense material surrounding the fissile material *Tamper, to interfere with, falsify, or sabotage * ...
of the weapon would be made of . When the bomb exploded, the excess neutrons from the
nuclear fission Nuclear fission is a nuclear reaction, reaction in which the atomic nucleus, nucleus of an atom splits into two or more smaller atomic nucleus, nuclei. The fission process often produces gamma ray, gamma photons, and releases a very large ...
would irradiate the cobalt and transmute it into . No country is known to have done any serious development of this type of weapon.


Production

There is no natural in existence on earth; thus, synthetic is created by bombarding a target with a slow neutron source. Californium-252, moderated through water, can be used for this purpose, as can the neutron flux in a
nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...
. The CANDU reactors can be used to activate , by substituting the control rods with cobalt rods. In the United States, it is now being produced in a
BWR A boiling water reactor (BWR) is a type of light water nuclear reactor used for the generation of electrical power. It is a design different from a Soviet graphite-moderated RBMK. It is the second most common type of electricity-generating nuc ...
at Hope Creek Nuclear Generating Station. The cobalt targets are substituted here for a small number of fuel assemblies. Still, over 40% of all
single-use medical device Single-use medical devices include any medical equipment, instrument or apparatus having the ability to only be used once in a hospital or clinic and then disposed. The Food and Drug Administration defines this as any device entitled by its manu ...
s are sterilized using from Bruce nuclear generating station. : + n →


Safety

After entering a living mammal (such as a human being), some of the is excreted in
feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a rela ...
. The remainder is taken up by tissues, mainly the
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
,
kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; bloo ...
s, and
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, an ...
s, where the prolonged exposure to gamma radiation can cause cancer. Over time, the absorbed cobalt is eliminated in urine.


Steel contamination

Cobalt is an element used to make steel. Uncontrolled disposal of in
scrap metal Scrap consists of recyclable materials, usually metals, left over from product manufacturing and consumption, such as parts of vehicles, building supplies, and surplus materials. Unlike waste, scrap has monetary value, especially recovered m ...
is responsible for the radioactivity found in several iron-based products. Circa 1983, construction was finished of 1700 apartments in Taiwan which were built with steel contaminated with cobalt-60. Approximately 10,000 people occupied these buildings during a 9–20 year period. On average, these people unknowingly received a radiation dose of 0.4 Sv. This large group did not suffer a higher incidence of cancer mortality, as the linear no-threshold model would predict, but suffered a lower cancer mortality than the general Taiwan public. These observations appear to be compatible with the radiation hormesis model. In August 2012, Petco recalled several models of steel pet food bowls after US Customs and Border Protection determined that they were emitting low levels of radiation. The source of the radiation was determined to be that had contaminated the steel. In May 2013 a batch of metal-studded belts sold by online retailer
ASOS ASOS or Asos may refer to: * Asos, a village in Greece * ASOS (retailer), a UK online fashion store * Association Sportive Oussou Saka, a Beninese football team * Automated Surface Observing System, a type of weather station * Air Support Oper ...
were confiscated and held in a US radioactive storage facility after testing positive for .


Incidents involving medical radiation sources

In the Samut Prakan radiation accident in 2000, a disused radiotherapy head containing a source was stored at an unsecured location in
Bangkok Bangkok, officially known in Thai as Krung Thep Maha Nakhon and colloquially as Krung Thep, is the capital and most populous city of Thailand. The city occupies in the Chao Phraya River delta in central Thailand and has an estimated populatio ...
, Thailand and then accidentally sold to scrap collectors. Unaware of the dangers, a junkyard employee dismantled the head and extracted the source, which remained unprotected for a period of days at the junkyard. Ten people, including the scrap collectors and workers at the junkyard, were exposed to high levels of radiation and became ill. Three of the junkyard workers subsequently died as a result of their exposure, which was estimated to be over 6  Gy. Afterward, the source was safely recovered by Thai authorities. In December 2013, a truck carrying a disused 111 TBq 60Co teletherapy source from a hospital in Tijuana to a
radioactive waste Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weap ...
storage center was hijacked at a gas station near
Mexico City Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley of ...
. The truck was soon recovered, but the thieves had removed the source from its shielding. It was found intact in a nearby field. Despite early reports with lurid headlines asserting that the thieves were "likely doomed", the radiation sickness was mild enough that the suspects were quickly released to police custody, and no one is known to have died from the incident.


Parity

In 1957, Chien-Shiung Wu et al. discovered the β-decay process violated
parity Parity may refer to: * Parity (computing) ** Parity bit in computing, sets the parity of data for the purpose of error detection ** Parity flag in computing, indicates if the number of set bits is odd or even in the binary representation of the r ...
, implying nature has a handedness. In the Wu experiment her group aligned radioactive nuclei by cooling the source to low temperatures in a magnetic field. Wu's observation was that more β-rays were emitted in the opposite direction to the nuclear spin. This asymmetry violates parity conservation.


Suppliers

Argentina, Canada and Russia are the largest suppliers of in the world. Both Argentina and Canada have (as of 2022) an all heavy water reactor fleet for power generation. Canada has the CANDU in numerous locations throughout Ontario as well as Point Lepreau Nuclear Generating Station in New Brunswick, while Argentina has two German supplied heavy water reactors at
Atucha nuclear power plant The Atucha Nuclear Complex, or Atucha Nuclear Power Plant, is the location for two adjacent nuclear power plants in Lima, Buenos Aires, Lima, Zárate Partido, Zárate, Buenos Aires Province, about from Buenos Aires, on the right-hand shore of ...
and a Canadian-built CANDU at
Embalse Nuclear Power Station The Embalse Nuclear Power Station ( es, Central Nuclear Embalse) is one of three operational nuclear power plants in Argentina. It is located on the southern shore of a reservoir on the Río Tercero, near the city of Embalse, Córdoba, 110&n ...
. Heavy water reactors are particularly well suited for the production of cobalt-60 because of their excellent neutron economy and because their capacity for online refueling allows targets to be inserted into the reactor core and removed after a predetermined time without the need for cold shutdown. Furthermore the heavy water used as a moderator is commonly held at lower temperatures than the coolant in light water reactors, allowing for a lower speed of neutrons, which increases the neutron cross section and decreases unwanted (n,2n) "knockout" reactions.


See also

* Cobalt bomb *
Harold E. Johns Harold Elford Johns (4 July 1915 – 23 August 1998) was a Canadian medical physicist, noted for his extensive contributions to the use of ionizing radiation to treat cancer. Early life and education Johns was born to missionary parents in S ...


References


External links


Cobalt-60
Centers for Disease Control and Prevention.
NLM Hazardous Substances Databank – Cobalt, Radioactive


HyperPhysics, Georgia State University. * {{Isotope, element=cobalt, lighter= cobalt-59, heavier=
cobalt-61 Naturally occurring cobalt (Co) consists of a single stable isotope, Co. Twenty-eight radioisotopes have been characterized; the most stable are Cobalt-60, Co with a half-life of 5.2714 years, Co (271.8 days), Co (77.27 days), and Co (70.86 days). ...
, before= iron-60, after= nickel-60 Isotopes of cobalt Radioactive contamination