Radionuclides which emit gamma radiation are valuable in a range of different industrial, scientific and medical technologies. This article lists some common gamma-emitting of technological importance, and their properties.
Fission products
Caesium-137 is one such radionuclide. It has a half-life of 30 years, and decays by beta decay without gamma ray emission to a metastable state of barium-137 (). Barium-137m has a half-life of a 2.6 minutes and is responsible for all of the gamma ray emission in this decay sequence. The ground state of barium-137 is stable.
The photon energy (energy of a single gamma ray) of is about 662 keV. These gamma rays can be used, for example, in radiotherapy such as for the treatment of cancer, in food irradiation, or in industrial gauges or sensors. is not widely used for industrial radiography as other nuclides, such as cobalt-60 or iridium-192, offer higher radiation output for a given volume.
Iodine-131 is another important gamma-emitting radionuclide produced as a fission product. With a short half-life of 8 days, this radioisotope is not of practical use in radioactive sources in industrial radiography or sensing. However, since iodine is a component of biological molecules such as thyroid hormones, iodine-131 is of great importance in nuclear medicine, and in medical and biological research as a radioactive tracer.
Lanthanum-140 is a decay product of barium-140, a common fission product. It is a potent gamma emitter. It was used in high quantities during the Manhattan Project for the .
Activation products
In addition to their uses in radiography, both cobalt-60 () and iridium-192 () are used in the radiotherapy of cancer. Cobalt-60 tends to be used in teletherapy units as a higher photon energy alternative to caesium-137, while iridium-192 tends to be used in a different mode of therapy, internal radiotherapy or brachytherapy. The iridium wires for brachytherapy are a palladium-coated iridium/palladium alloy wire made radioactive by neutron activation. This wire is then inserted into a tumor such as a breast tumor, and the tumor is irradiated by gamma ray photons from the wire. At the end of the treatment the wire is removed.
A rare but notable gamma source is sodium-24; this has a fairly short half-life of 15 hours, but it emits photons with very high energies (>2 MeV). It could be used for radiography of thick steel objects if the radiography occurred close to the point of production. Similarly to and , it is formed by the neutron activation of the commonly found stable isotope.
Minor actinides
Natural radioisotopes
Table of some useful gamma emitting isotopes
| +Useful Gamma emitting isotopes |
| This isotope also undergoes β+ decay, which produces two electron mass gamma rays at opposite directions via annihilation with electrons, thus making this isotope an indirect source of such gammas. |
| Co-60 emits two distinct gammas of high energy (total energy is 2.5 MeV) |
| used in industrial radiography |
| used in a variety of nuclear medicine imaging procedures |
| used in brachytherapy |
| used in brachytherapy |
| used in brachytherapy |
| sometimes still used in radiotherapy and industrial application for measuring the density, liquid level, humidity and many more |
| used for early radiotherapy (pre Cs-137 and Co-60 circa 1950's) |
| Used in most smoke detectors |
Note only half-lives between 100 min and 5,000 yr are listed as short half-lives are usually not practical to use, and long half-lives usually mean extremely low specific activity. d = day, hr = hour, yr = year.
See also
- Isotopes of caesium
- Common beta emitters
- List of alpha-emitting nuclides
External links
- http://www.iem-inc.com/information/tools/radiation-energies/gamma-emitters
- useful radioisotope search tool
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