Cobalt-60: Difference between revisions
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{{nuclide|cobalt|60}} could be used to "salt" a [[cobalt bomb]]. This a hypothetically-feasible but extremely "dirty" form of [[nuclear weapon]] that has never been produced. Hypothetically, a [[nuclear bomb]] with a [[tamper]] of {{nuclide|cobalt|59}} would irradiate the cobalt with excess neutrons from the [[nuclear fission]] and transmute it into {{nuclide|cobalt|60}}. |
{{nuclide|cobalt|60}} could be used to "salt" a [[cobalt bomb]]. This a hypothetically-feasible but extremely "dirty" form of [[nuclear weapon]] that has never been produced. Hypothetically, a [[nuclear bomb]] with a [[tamper]] of {{nuclide|cobalt|59}} would irradiate the cobalt with excess neutrons from the [[nuclear fission]] and transmute it into {{nuclide|cobalt|60}}. |
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The creation of {{nuclide|cobalt|60}} is an important step in [[nucleosynthesis]]. Without the step through {{nuclide|cobalt|60}}, no elements with [[atomic number]]s from 27 through 83 |
The creation of {{nuclide|cobalt|60}} is an important step in [[nucleosynthesis]]. Without the step through {{nuclide|cobalt|60}}, no elements with [[atomic number]]s from 27 through 83 could be created in [[supernova]]s.<ref>[http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/AT321/HTML/AT32104.HTM The Formation of the Elements]</ref><!-- some more explanations available?--> |
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==Occurrence== |
==Occurrence== |
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Revision as of 20:02, 5 November 2010
| General | |
|---|---|
| Symbol | 60Co |
| Names | cobalt-60, 60Co, Co-60 |
| Protons (Z) | 27 |
| Neutrons (N) | 33 |
| Nuclide data | |
| Natural abundance | 0 (artificial element) |
| Half-life (t1/2) | 1925.1 d |
| Isotope mass | 59.9338222 Da |
| Spin | 5+ |
| Decay modes | |
| Decay mode | Decay energy (MeV) |
| Beta | 2.824 [1] |
| Isotopes of cobalt Complete table of nuclides | |
Cobalt-60, 60
27Co
, is a synthetic radioactive isotope of cobalt. Due to its short half life of 5.27 years, 60
27Co
is not found in nature. It is produced artificially by neutron activation of 59
27Co
. 60
27Co
decays by beta decay to the stable isotope nickel-60 (60
28Ni
). The activated nickel nucleus emits two gamma rays with energies of 1.17 and 1.33 MeV, hence the overall nuclear equation of the reaction is
59
27Co
+ n → 60
27Co
→ 60
28Ni
+ e + gamma rays.
Activity
Corresponding to its half life the radioactive activity of one gram of 60
27Co
is 44 TBq (about 1100 curies). The absorbed dose constant is related to the decay energy and time. For 60
27Co
it is equal to 0.35 mSv/(GBq h). This allows calculation of the equivalent dose, which depends on distance and activity.
Example: a 60
27Co
source with an activity of 2.8 GBq, which is equivalent to 60 µg of pure 60
27Co
, generates a dose of 1 mSv in one meter distance within one hour. The swallowing of 60
27Co
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 <100 kBq. Devices for nondestructive material testing uses sources with activities of 1 TBq and more.
The high γ-energies result in a significant mass difference between 60
28Ni
and 60
27Co
of 0.003 u. The short life time contributes further to the high decay energy. This amounts to nearly 20 watts per gram, nearly 30 times larger than that of 238
94Pu
.
Decay scheme
The diagram shows a (simplified) decay scheme of 60
27Co
and 60mCo. 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.[2] Internal conversion energies are well below the main energy levels.
60mCo is a nuclear isomer of 60
27Co
. After a half-life of 10.467 minutes and emission of 58.59 keV gamma rays it transforms into 60
27Co
:
- Co60m(IT)Co60
With a low probability 60mCo also β-decays and populates the two "2+" levels of 60
28Ni
.
Applications
The β-decay energy is low and easily shielded. Both strong gamma-ray frequencies are about the same magnitude, therefore 60
27Co
is used as a gamma-ray source with energies around 1.3 MeV.
Main uses for 60
27Co
:
- 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.
60
27Co
might be an efficient heater for a radioisotope thermoelectric generator. However, in contrast to the commonly-used 238
94Pu
, its power is nearly exhausted after 10 years. It is also more difficult to absorb the γ-ray power of 60
27Co
than the power of α-particles emitted by plutonium-238.
60
27Co
could be used to "salt" a cobalt bomb. This a hypothetically-feasible but extremely "dirty" form of nuclear weapon that has never been produced. Hypothetically, a nuclear bomb with a tamper of 59
27Co
would irradiate the cobalt with excess neutrons from the nuclear fission and transmute it into 60
27Co
.
The creation of 60
27Co
is an important step in nucleosynthesis. Without the step through 60
27Co
, no elements with atomic numbers from 27 through 83 could be created in supernovas.[3]
Occurrence
Due to its the quite short half-life, there is no natural 60
27Co
in existence. Synthetic 60
27Co
is created by bombarding a 59
27Co
target with a slow neutron source, usually californium-252 moderated through water to slow the neutrons down, or in a nuclear reactor such as a CANDU reactor, where the control rods usually made of steel are instead made of 59
27Co
[4]:
- 59
27Co
+ n → 60
27Co
Safety
After entering a living mammal (such as a human being), most of the 60
27Co
gets excreted in feces. A small amount is absorbed by the liver, the kidneys, and the bones, where the prolonged exposure to gamma radiation can cause cancer.
Cobalt is an element of steel alloys. Uncontrolled disposal of 60
27Co
in scrap metal is responsible for the radioactivity found in several iron-based products.[5][6]
See also
References
- ^ Korea Atomic Energy Research Institute. "Nuclide Table". Retrieved 2009-03-14.
- ^ Co60 energy levels
- ^ The Formation of the Elements
- ^ Isotope Production: Dual Use Power Plants
- ^ radioactive contamination of steel
- ^ "Lessons Learned The Hard Way". IAEA Bulletin 47-2. International Atomic Energy Agency. Retrieved 16 April 2010.
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.