Commonly-used gamma emitting isotopes
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== Fission products ==
'''[[Caesium-137]]''' is a [[radioactivity|radioactive]] [[isotope]] which is formed mainly by [[nuclear fission]]. It has a [[half-life]] of 30 years, and decays by pure [[beta decay]] to a [[metastable]] state of [[barium]]-137 ([[Ba-137m]]). Barium-137m has a half-life of minutes and is responsible for all of the [[gamma ray]] emission. The ground state of [[barium-137]] is stable.
The [[photon]] energy of Ba-137m is about 662 keV. These photons can be used in [[Food irradiation|food irradation]], or in [[cancer]] treatment. Cs-137 is not widely used for industrial [[radiography]] as other isotopes offer higher gamma activities for a given volume. For instance, [[cobalt-60]] and [[iridium-192]] can be made by the [[neutron irradiation]] of normal non-radioactive [[cobalt]] and [[iridium]] metal.
== Activation products ==
In addition to their uses in radiography, both [[cobalt]]-60 ([[Co-60]]) and [[iridium]]-192 ([[Ir-192]]) are used in the [[radiotherapy]] of cancer. [[Cobalt]]-60 tends to be used in [[teletherapy]] units as a higher photon energy alternative to Cs-137, while iridium-192 tends to be used in a different mode of therapy ([[brachytherapy]]). The iridium wires for brachythereapy 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 very short half life 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. In common with Co-60 and Ir-192 it is formed by the [[neutron activation]] of the commonly found stable isotope.
== [[Minor actinides]] ==
[[Americium]]-241 has been used as a source of low energy gamma photons, it has been used in some applications such as portable X-ray [[fluorescence]] equipment ([[XRF]]).
== Natural radioisotopes ==
Many years ago [[radium]]-226 and [[radon]]-222 sources were used as [[photon]] sources for industrial [[radiography]]: for instance a [[radon]]-222 source was used to examine the mechanisms inside an unexploded [[V-1 flying bomb]], while some of the early [[Bathysphere (vessel)|Bathyspheres]] could be examined using radium-226 to check for cracks. Due to the fact that both radium and radon are very radiotoxic (and expensive), these natural radioisotopes have fallen out of use. For industrial radiography, [[iridium]]-192 and [[cobalt]]-60 can be used as photon sources as both of these are much shorter lived than radium-226 and are less radiotoxic.
== [[Cyclotron]] generated ==
[[Iodine-125]] is used in a variety of [[biochemical]] assays. Often, <sup>125</sup>I is conjugated to the [[tyrosine]] of a target [[protein]]. This protein can then be followed by monitoring the gamma radiation. With the advent of non-radioactive fluorogenic labels, the use of [[Iodine]]-125 has fallen off.
==See also==
* [[Caesium]], [[Caesium-137|Cs-137]]
* [[Isotopes of caesium]]
* [[Common beta emitters]]
[[Category:Particle physics]]
[[Category:Nuclear physics]]
[[Category:Nuclear chemistry]]
[[Category:Radioactivity]]
[[Category:Isotopes]]
[[Category:Nuclear materials]]