{{Short description|none}} {{more citations needed|date=July 2022}} Radionuclides which emit [[gamma radiation]] are valuable in a range of different industrial, scientific and medical technologies. This article lists some common gamma-emitting [[radionuclide]]s of technological importance, and their properties.
==Fission products== Many [[synthetic radioisotope|artificial radionuclides]] of technological importance are produced as fission products within [[nuclear reactor]]s. A [[fission product]] is a nucleus with approximately half the mass of a uranium or plutonium nucleus which is left over after such a nucleus has been "split" in a [[nuclear fission]] reaction.
[[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 ({{SimpleNuclide|barium|137|m|link=yes}}). 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 {{SimpleNuclide|barium|137|m}} 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. {{SimpleNuclide|caesium|137}} 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 [[RaLa Experiment]]s.
== Activation products ==
Some radionuclides, such as [[cobalt-60]] and [[iridium-192]], are made by the [[neutron irradiation]] of normal non-radioactive [[cobalt]] and [[iridium]] metal in a [[nuclear reactor]], creating radioactive nuclides of these elements which contain extra neutrons, compared to the original stable nuclides.
In addition to their uses in radiography, both cobalt-60 ({{SimpleNuclide|Co|60}}) and [[iridium-192]] ({{SimpleNuclide|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 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 [[Isotopes of sodium#Sodium-24|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 {{SimpleNuclide|Co|60}} and {{SimpleNuclide|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 ([[X-ray fluorescence|XRF]]) and common household [[Smoke detector#Ionization|ionizing smoke detector]]s. Americium-241 is produced from {{chem|239|Pu}} in nuclear reactors through multiple [[neutron capture]]s and subsequent [[beta decay]]s with the plutonium-239 itself being produced mostly from neutron capture and subsequent beta decays by {{chem|238|U}} (99% of [[natural uranium]] and usually roughly 97% of [[Enriched uranium#Low enriched uranium (LEU)|low enriched uranium]] or [[MOX fuel]]).
== Natural radioisotopes ==
Many years ago [[radium-226]] and [[radon-222]] were used as gamma-ray 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]]s could be examined using radium-226 to check for cracks. Because both [[radium]] and [[radon]] are very radiotoxic and very expensive due to their natural rarity, these natural radioisotopes have fallen out of use over the last half-century, replaced by artificially created radioisotopes. [[Radon therapy]] sits on the edge of [[radioactive quackery]] and genuine [[radiotherapy]] in part due to the lack of reliable data on the stated health benefits.
==Table of some useful gamma emitting isotopes== {| class="wikitable sortable" style="text-align:center" |+Useful Gamma emitting isotopes |- ! Isotope !! atomic mass !! half-life !! Emitted Gamma energy (MeV) !! Notes |- | Be-7 ||7 || 53 d || 0.48 || |- | Na-22 ||22 || 2.6 yr || 1.28 || This isotope also undergoes [[positron emission|β<sup>+</sup> decay]], which produces two [[electron mass|0.511 MeV]] gamma rays at opposite directions via annihilation with electrons, thus making this isotope an indirect source of such gammas. |- | Na-24 ||24 || 15 hr || 1.37 || |- | Mn-54 ||54 || 312 d || 0.84 || |- | Co-57 ||57 || 272 d || 0.122 || |- | rowspan=2|Co-60 ||rowspan=2|60 || rowspan=2|5.265 yr || 1.17 || Co-60 emits two distinct gammas of high energy (total energy is 2.5 MeV) <ref>{{cite web | url=https://pubchem.ncbi.nlm.nih.gov/compound/cobalt-60#section=Hazards-Summary&fullscreen=true | title=Cobalt-60 }}</ref> |- | 1.33 || used in industrial radiography |- | Zn-65 ||65 || 244 d || 1.115<ref>{{cite journal| last1 = Roost | first1 = E. | last2 = Funck | first2 = E. | last3 = Spernol | first3 = A. | last4 = Vaninbroukx | first4 = R. | title = The decay of <sup>65</sup>Zn | journal = Zeitschrift für Physik | volume = 250 | issue = 5 | pages = 395–412 | year = 1972 | doi = 10.1007/BF01379752|bibcode = 1972ZPhy..250..395D | s2cid = 124728537 }}</ref> || |- | Ga-66 ||66 || 9.4 hr || 1.04 || |- | Tc-99m ||99 || 6 hr || 0.14 || used in a variety of nuclear medicine imaging procedures |- | Pd-103 ||103 || 17 d || 0.021 || used in brachytherapy |- | Ag-112 ||112 || 3.13 hr|| 0.62 || |- | Sn-113 ||113 || 115 d || 0.392 || |- | Te-132 ||132 || 77 hr || 0.23 || |- | I-125 ||125 || 60 d || 0.035 || used in brachytherapy |- | I-131 ||131 || 8 d || 0.364 || used in brachytherapy |- | Xe-133 ||133 || 5.24 d || 0.08 || |- | Cs-134 ||134 || 2.06 yr || 0.61 || |- | Cs-137 ||137 || 30.17 yr || 0.662 || sometimes still used in radiotherapy and industrial application for measuring the density, liquid level, humidity and many more |- | Ba-133 ||133 || 10.5 yr || 0.356 || |- | Ce-144 ||144 || 285 d || 0.13 || |- | Rn-222 ||222 || 3.8 d || 0.51 || |- | Ra-226 ||226 || 1600 yr || 0.19 || used for early radiotherapy (pre Cs-137 and Co-60 circa 1950's) |- | Am-241 || 241 || 432 yr || 0.06 || 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 * [http://nucleardata.nuclear.lu.se/toi/radSearch.asp useful radioisotope search tool]
==References== {{Reflist}}
[[Category:Gamma rays]] [[Category:Isotopes]] [[Category:Nuclear chemistry]] [[Category:Nuclear materials]] [[Category:Nuclear physics]] [[Category:Radioactivity]]