Editing Caesium (section)

==Applications==

===Petroleum exploration===<!-- linked from "Formate" article -->
The largest present-day use of nonradioactive caesium is in [[formate|caesium formate]] [[drilling fluid]]s for the [[extractive oil industry]].<ref name="USGS"/> Aqueous solutions of caesium formate (HCOO<sup>−</sup>Cs<sup>+</sup>)—made by reacting caesium hydroxide with [[formic acid]]—were developed in the mid-1990s for use as oil well drilling and [[completion (oil and gas wells)|completion fluids]]. The function of a drilling fluid is to lubricate drill bits, to bring rock cuttings to the surface, and to maintain pressure on the formation during drilling of the well. Completion fluids assist the emplacement of control hardware after drilling but prior to production by maintaining the pressure.<ref name="USGS"/>

The high density of the caesium formate brine (up to 2.3&nbsp;g/cm<sup>3</sup>, or 19.2&nbsp;pounds per gallon),<ref name="Down">{{cite conference |conference=IADC/SPE Drilling Conference |date=February 2006 |location=Miami, Florida, USASociety of Petroleum Engineers |first1=J. D. |last1=Downs |first2=M. |last2=Blaszczynski |first3=J. |last3=Turner |first4=M. |last4=Harris |doi=10.2118/99068-MS |url=http://www.spe.org/elibinfo/eLibrary_Papers/spe/2006/06DC/SPE-99068-MS/SPE-99068-MS.htm |archive-url=https://web.archive.org/web/20071012122901/http://spe.org/elibinfo/eLibrary_Papers/spe/2006/06DC/SPE-99068-MS/SPE-99068-MS.htm |archive-date=12 October 2007 |title=Drilling and Completing Difficult HP/HT Wells With the Aid of Cesium Formate Brines-A Performance Review}}</ref> coupled with the relatively benign nature of most caesium compounds, reduces the requirement for toxic high-density suspended solids in the drilling fluid—a significant technological, engineering and environmental advantage. Unlike the components of many other heavy liquids, caesium formate is relatively environment-friendly.<ref name="Down"/> Caesium formate brine can be blended with potassium and sodium formates to decrease the density of the fluids to that of water (1.0&nbsp;g/cm<sup>3</sup>, or 8.3&nbsp;pounds per gallon). Furthermore, it is biodegradable and may be recycled, which is important in view of its high cost (about $4,000&nbsp;per [[barrel (volume)#Oil barrel|barrel]] in 2001).<ref>{{cite journal |last=Flatern |first=Rick |date=2001 |title=Keeping cool in the HPHT environment |journal=Offshore Engineer |issue=February |pages=33–37}}</ref> Alkali formates are safe to handle and do not damage the producing formation or downhole metals as corrosive alternative, high-density brines (such as [[zinc bromide]] {{Chem|ZnBr|2}} solutions) sometimes do; they also require less cleanup and reduce disposal costs.<ref name="USGS"/>

===Atomic clocks===
[[File:Usno-mc.jpg|thumb|Atomic clock ensemble at the U.S. Naval Observatory|alt=A room with a black box in the foreground and six control cabinets with space for five to six racks each. Most, but not all, of the cabinets are filled with white boxes.]]
Caesium-based [[atomic clock]]s use the [[electromagnetic radiation|electromagnetic transitions]] in the [[hyperfine structure]] of caesium-133 atoms as a reference point. The first accurate caesium clock was built by [[Louis Essen]] in 1955 at the [[National Physical Laboratory, UK|National Physical Laboratory]] in the UK.<ref>{{cite journal |first1=L. |last1=Essen |first2=J. V. L. |last2=Parry |date=1955 |title=An Atomic Standard of Frequency and Time Interval: A Caesium Resonator |journal=[[Nature (journal) |Nature]] |volume=176 |pages=280–282 |doi=10.1038/176280a0 |bibcode=1955Natur.176..280E |issue=4476 |s2cid=4191481}}</ref> Caesium clocks have improved over the past half-century and are regarded as "the most accurate realization of a unit that mankind has yet achieved."<ref name="USNO"/> These clocks measure frequency with an error of 2 to 3&nbsp;parts in 10<sup>14</sup>, which corresponds to an accuracy of 2&nbsp;[[nanosecond]]s per day, or one second in 1.4&nbsp;million&nbsp;years. The latest versions are more accurate than 1 part in 10<sup>15</sup>, about 1 second in 20&nbsp;million years.<ref name="USGS"/> The [[caesium standard]] is the primary standard for standards-compliant time and frequency measurements.<ref>{{cite journal |last1=Markowitz |first1=W. |last2=Hall |first2=R. |last3=Essen |first3=L. |last4=Parry |first4=J. |title=Frequency of Cesium in Terms of Ephemeris Time |doi=10.1103/PhysRevLett.1.105 |journal=Physical Review Letters |volume=1 |issue=3 |pages=105–107 |year=1958 |bibcode=1958PhRvL...1..105M}}</ref> Caesium clocks regulate the timing of cell phone networks and the Internet.<ref>{{cite news |first=Monte |last=Reel |date=22 July 2003 |title=Where timing truly is everything |newspaper=The Washington Post |page=B1 |url=http://www.highbeam.com/doc/1P2-284155.html |access-date=26 January 2010 |archive-url=https://web.archive.org/web/20130429044454/http://www.highbeam.com/doc/1P2-284155.html |archive-date=29 April 2013 |url-status=dead}}</ref>

====Definition of the second====
The second, symbol ''s'', is the SI unit of time. The [[BIPM]] restated its definition at its 26th conference in 2018: "[The second] is defined by taking the fixed numerical value of the caesium frequency {{math|Δ''ν''<sub>Cs</sub>}}, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be {{val|9192631770}} when expressed in the unit [[Hz]], which is equal to s<sup>−1</sup>."<ref>{{cite web |title=Resolution 1 of the 26th CGPM |url=https://www.bipm.org/en/CGPM/db/26/1/ |publisher=Bureau International des Poids et Mesures |location=Paris |pages=472 of the official French publication |language=FR,EN |date=2018 |access-date=2019-12-29 |archive-date=2021-02-04 |archive-url=https://web.archive.org/web/20210204120336/https://www.bipm.org/en/CGPM/db/26/1/ |url-status=dead }}</ref>

===Electric power and electronics===
Caesium vapour [[thermionic converter|thermionic generators]] are low-power devices that convert heat energy to electrical energy. In the two-electrode [[vacuum tube]] converter, caesium neutralizes the space charge near the cathode and enhances the current flow.<ref>{{cite journal |last1=Rasor |first1=Ned S. |first2=Charles |last2=Warner |title=Correlation of Emission Processes for Adsorbed Alkali Films on Metal Surfaces |journal=Journal of Applied Physics |volume=35 |issue=9 |pages=2589–2600 |date=September 1964 |doi=10.1063/1.1713806 |bibcode=1964JAP....35.2589R}}</ref>

Caesium is also important for its [[photoelectric effect|photoemissive]] properties, converting light to electron flow. It is used in [[solar cell|photoelectric cells]] because caesium-based cathodes, such as the intermetallic compound {{chem|K|2|CsSb}}, have a low threshold voltage for emission of [[electron]]s.<ref>{{cite web |url=https://www.americanelements.com/cs.html |title=Cesium Supplier & Technical Information |publisher=American Elements |access-date=25 January 2010 |archive-date=7 October 2023 |archive-url=https://web.archive.org/web/20231007071144/https://www.americanelements.com/cs.html |url-status=live }}</ref> The range of photoemissive devices using caesium include [[optical character recognition]] devices, [[photomultiplier|photomultiplier tubes]], and [[video camera tube]]s.<ref>{{cite journal |doi=10.1063/1.3215593 |title=K<sub>2</sub>CsSb Cathode Development |journal=AIP Conference Proceedings |date=2009 |volume=1149 |issue=1 |pages=1062–1066 |first1=John |last1=Smedley |first2=Triveni |last2=Rao|author2-link=Triveni Rao |first3=Erdong |last3=Wang |bibcode=2009AIPC.1149.1062S}}</ref><ref>{{cite journal |first=P. |last=Görlich |title=Über zusammengesetzte, durchsichtige Photokathoden |journal=Zeitschrift für Physik |volume=101 |pages=335–342 |date=1936 |doi=10.1007/BF01342330 |bibcode=1936ZPhy..101..335G |issue=5–6 |s2cid=121613539}}</ref> Nevertheless, [[germanium]], rubidium, selenium, silicon, tellurium, and several other elements can be substituted for caesium in photosensitive materials.<ref name="USGS"/>

[[Caesium iodide]] (CsI), [[caesium bromide|bromide]] (CsBr) and [[caesium fluoride|fluoride]] (CsF) crystals are employed for [[scintillator]]s in [[scintillation counter]]s widely used in mineral exploration and particle physics research to detect [[gamma ray|gamma]] and [[X-ray]] radiation. Being a heavy element, caesium provides good stopping power with better detection. Caesium compounds may provide a faster response (CsF) and be less hygroscopic (CsI).

Caesium vapour is used in many common [[magnetometer]]s.<ref>{{cite journal |doi=10.1007/s00340-005-1773-x |title=Comparison of discharge lamp and laser pumped cesium magnetometers |date=2005 |last1=Groeger |first1=S. |first2=A. S. |first3=A. |journal=Applied Physics B |volume=80 |pages=645–654 |last2=Pazgalev |last3=Weis |arxiv=physics/0412011 |bibcode=2005ApPhB..80..645G |issue=6 |s2cid=36065775}}</ref>

The element is used as an [[internal standard]] in [[spectrophotometry]].<ref>{{cite book |chapter-url=https://books.google.com/books?id=z9SzvsSCHv4C&pg=PA108 |page=108 |isbn=978-0-471-28572-4 |chapter=Internal Standards |date=1994 |first1=Mary C. |last1=Haven |first2=Gregory A. |last2=Tetrault |first3=Jerald R. |last3=Schenken |publisher=John Wiley and Sons |location=New York |title=Laboratory instrumentation |access-date=8 May 2021 |archive-date=5 March 2024 |archive-url=https://web.archive.org/web/20240305132946/https://books.google.com/books?id=z9SzvsSCHv4C&pg=PA108#v=onepage&q&f=false |url-status=live }}</ref> Like other [[alkali metal]]s, caesium has a great affinity for [[oxygen]] and is used as a "[[getter]]" in [[vacuum tube]]s.<ref>{{cite book |url=https://books.google.com/books?id=1o1WECNJkscC&pg=PA391 |title=Photo-electronic image devices: proceedings of the fourth symposium held at Imperial College, London, 16–20 September 1968 |volume=1 |publisher=Academic Press |date=1969 |first=James D. |last=McGee |page=391 |isbn=978-0-12-014528-7 |access-date=8 May 2021 |archive-date=5 March 2024 |archive-url=https://web.archive.org/web/20240305132838/https://books.google.com/books?id=1o1WECNJkscC&pg=PA391#v=onepage&q&f=false |url-status=live }}</ref> Other uses of the metal include high-energy [[laser]]s, [[fluorescent lamp|vapour glow lamps]], and vapour [[rectifier]]s.<ref name="USGS"/>

===Centrifugation fluids===
The high density of the caesium ion makes solutions of caesium chloride, caesium sulfate, and caesium [[trifluoroacetic acid|trifluoroacetate]] ({{chem|Cs(O|2|CCF|3|)}}) useful in molecular biology for density gradient [[differential centrifugation|ultracentrifugation]].<ref>Manfred Bick, Horst Prinz, "Cesium and Cesium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a06_153}}.</ref> This technology is used primarily in the isolation of [[virus|viral particles]], subcellular [[organelle]]s and fractions, and [[nucleic acid]]s from biological samples.<ref>{{cite book |chapter-url=https://books.google.com/books?id=1kn89nI2gUsC&pg=PA61 |pages=61–62 |isbn=978-0-89603-564-5 |chapter=Gradient Materials |editor=Desai, Mohamed A. |date=2000 |publisher=Humana Press |location=Totowa, N.J. |title=Downstream processing methods |access-date=8 May 2021 |archive-date=5 March 2024 |archive-url=https://web.archive.org/web/20240305133410/https://books.google.com/books?id=1kn89nI2gUsC&pg=PA61#v=onepage&q&f=false |url-status=live }}</ref>

===Chemical and medical use===
[[File:Caesium chloride.jpg|thumb|alt=Some fine white powder on a laboratory watch glass|Caesium chloride powder]]
Relatively few chemical applications use caesium.<ref>{{cite book |last=Burt |first=R. O. |date=1993 |chapter=Cesium and cesium compounds |title=Kirk-Othmer encyclopedia of chemical technology |edition=4th |place=New York |publisher=John Wiley & Sons |volume=5 |page=759 |isbn=978-0-471-15158-6}}</ref> Doping with caesium compounds enhances the effectiveness of several metal-ion catalysts for chemical synthesis, such as [[acrylic acid]], [[anthraquinone]], [[ethylene oxide]], [[methanol]], [[phthalic anhydride]], [[styrene]], [[methyl methacrylate]] monomers, and various [[alkene|olefins]]. It is also used in the catalytic conversion of [[sulfur dioxide]] into [[sulfur trioxide]] in the production of [[sulfuric acid]].<ref name="USGS"/> <!--No way: Caesium metal is also used in ferrous and nonferrous [[metallurgy]] and in the purification of [[carbon dioxide]] as it absorbs gases and other impurities, while molten hydroxide (CsOH) has been used in the desulfurizing of heavy crude oil.<ref name="USGS"/> -->

[[Caesium fluoride]] enjoys a niche use in [[organic chemistry]] as a [[base (chemistry)|base]]<ref name="greenwood">{{cite book |last1=Greenwood |first1=N. N. |last2=Earnshaw |first2=A. |title=Chemistry of the Elements |publisher=Pergamon Press |place=Oxford, UK |date=1984 |isbn=978-0-08-022057-4}}</ref> and as an [[anhydrous]] source of [[fluoride]] ion.<ref>
Friestad, Gregory K.; Branchaud, Bruce P.; Navarrini, Walter and Sansotera, Maurizio (2007) "Cesium Fluoride" in ''Encyclopedia of Reagents for Organic Synthesis'', John Wiley & Sons. {{doi|10.1002/047084289X.rc050.pub2}}</ref> Caesium salts sometimes replace potassium or sodium salts in [[organic synthesis]], such as [[cyclic compound|cyclization]], [[esterification]], and [[polymerization]]. Caesium has also been used in thermoluminescent radiation [[dosimetry]] <small>(TLD)</small>: When exposed to radiation, it acquires crystal defects that, when heated, revert with emission of light proportionate to the received dose. Thus, measuring the light pulse with a [[photomultiplier tube]] can allow the accumulated radiation dose to be quantified.

===Nuclear and isotope applications===
[[Caesium-137]] is a [[radionuclide|radioisotope]] commonly used as a [[gamma ray|gamma]]-emitter in industrial applications. Its advantages include a half-life of roughly 30 years, its availability from the [[nuclear fuel cycle]], and having [[Isotopes of barium|<sup>137</sup>Ba]] as a stable end product. The high water solubility is a disadvantage which makes it incompatible with large pool irradiators for food and medical supplies.<ref name="Takeshi">{{cite web |url=http://earth1.epa.gov/radiation/docs/source-management/csfinallongtakeshi.pdf |title=The material flow of radioactive cesium-137 in the U.S. 2000 |first=Takeshi |last=Okumura |date=21 October 2003 |access-date=20 December 2009 |publisher=United States Environmental Protection Agency |url-status=dead |archive-url=https://web.archive.org/web/20110720163223/http://earth1.epa.gov/radiation/docs/source-management/csfinallongtakeshi.pdf |archive-date=20 July 2011}}</ref> It has been used in agriculture, cancer treatment, and the [[sterilization (microbiology)|sterilization]] of food, sewage sludge, and surgical equipment.<ref name="USGS"/><ref>{{cite book |last=Jensen |first=N. L. |date=1985 |chapter=Cesium |title=Mineral facts and problems |publisher=U.S. Bureau of Mines |volume=Bulletin 675 |pages=133–138}}</ref> Radioactive [[isotopes of caesium]] in [[radiation therapy|radiation devices]] were used in the medical field to treat certain types of cancer,<ref>{{cite web |url=http://www.medicalnewstoday.com/releases/91994.php |title=IsoRay's Cesium-131 Medical Isotope Used In Milestone Procedure Treating Eye Cancers At Tufts-New England Medical Center |date=17 December 2007 |work=Medical News Today |access-date=15 February 2010 |archive-date=29 April 2021 |archive-url=https://web.archive.org/web/20210429030824/https://www.medicalnewstoday.com/releases/91994 |url-status=live }}</ref> but emergence of better alternatives and the use of water-soluble caesium chloride in the sources, which could create wide-ranging contamination, gradually put some of these caesium sources out of use.<ref>{{cite book |chapter-url=https://books.google.com/books?id=bk0go_-FO5QC&pg=PA22 |isbn=978-0-07-005115-7 |chapter=Caesium-137 Machines |title=Radiation therapy planning |first=Gunilla Carleson |last=Bentel |publisher=McGraw-Hill Professional |date=1996 |access-date=26 September 2010 |pages=22–23 |archive-date=5 March 2024 |archive-url=https://web.archive.org/web/20240305133453/https://books.google.com/books?id=bk0go_-FO5QC&pg=PA22 |url-status=live }}</ref><ref>{{cite book |isbn=978-0-309-11014-3 |url=https://books.google.com/books?id=3cT2REdXJ98C |title=Radiation source use and replacement: abbreviated version |author=National Research Council (U.S.). Committee on Radiation Source Use and Replacement |publisher=National Academies Press |date=2008 |access-date=11 October 2015 |archive-date=5 March 2024 |archive-url=https://web.archive.org/web/20240305133449/https://books.google.com/books?id=3cT2REdXJ98C |url-status=live }}</ref> Caesium-137 has been employed in a variety of industrial measurement gauges, including moisture, density, levelling, and thickness gauges.<ref name="gauges">{{cite book |chapter=Level and density measurement using non-contact nuclear gauges |isbn=978-0-412-53400-3 |chapter-url=https://books.google.com/books?id=RwsoQbHYjvwC&pg=PA82 |pages=82–85 |editor=Loxton, R. |editor2=Pope, P. |date=1995 |publisher=Chapman & Hall |location=London |title=Instrumentation : A Reader |access-date=8 May 2021 |archive-date=5 March 2024 |archive-url=https://web.archive.org/web/20240305133353/https://books.google.com/books?id=RwsoQbHYjvwC&pg=PA82#v=onepage&q&f=false |url-status=live }}</ref> It has also been used in [[well logging]] devices for measuring the [[electron density]] of the rock formations, which is analogous to the bulk density of the formations.<ref>{{cite journal |doi=10.1146/annurev.ea.13.050185.001531 |title=Downhole Geophysical Logging |date=1985 |last1=Timur |first1=A. |last2=Toksoz |first2=M. N. |journal=Annual Review of Earth and Planetary Sciences |volume=13 |pages=315–344 |bibcode=1985AREPS..13..315T}}</ref>

Caesium-137 has been used in [[hydrology|hydrologic]] studies analogous to those with [[tritium]]. As a daughter product of fission bomb testing from the 1950s through the mid-1980s, caesium-137 was released into the atmosphere, where it was absorbed readily into solution. Known year-to-year variation within that period allows correlation with soil and sediment layers. Caesium-134, and to a lesser extent caesium-135, have also been used in hydrology to measure the caesium output by the nuclear power industry. While they are less prevalent than either caesium-133 or caesium-137, these bellwether isotopes are produced solely from anthropogenic sources.<ref>{{cite web |first=Carol |last=Kendall |author-link=Carol Kendall (scientist) |url=http://wwwrcamnl.wr.usgs.gov/isoig/period/cs_iig.html |title=Isotope Tracers Project – Resources on Isotopes – Cesium |publisher=National Research Program – U.S. Geological Survey |access-date=25 January 2010 |archive-date=8 July 2021 |archive-url=https://web.archive.org/web/20210708104546/https://wwwrcamnl.wr.usgs.gov/isoig/period/cs_iig.html |url-status=live }}</ref><!--https://books.google.com/books?id=pWDQnxd-r1UC&pg=PT360 &pg=PT12 -->

===Other uses===
[[File:Electrostatic ion thruster-en.svg|thumb|upright=1.4|Schematics of an electrostatic ion thruster developed for use with caesium or mercury fuel|alt=Electrons beamed from an electron gun hit and ionize neutral fuel atoms; in a chamber surrounded by magnets, the positive ions are directed toward a negative grid that accelerates them. The force of the engine is created by expelling the ions from the rear at high velocity. On exiting, the positive ions are neutralized from another electron gun, ensuring that neither the ship nor the exhaust is electrically charged and are not attracted.]]
Caesium and mercury were used as a propellant in early [[ion thruster|ion engines]] designed for [[spacecraft propulsion]] on very long interplanetary or extraplanetary missions. The fuel was ionized by contact with a charged [[tungsten]] electrode. But corrosion by caesium on spacecraft components has pushed development in the direction of inert gas propellants, such as [[xenon]], which are easier to handle in ground-based tests and do less potential damage to the spacecraft.<ref name="USGS"/> Xenon was used in the experimental spacecraft [[Deep Space 1]] launched in 1998.<ref>{{cite journal |doi=10.1063/1.1150468 |title=NSTAR Xenon Ion Thruster on Deep Space 1: Ground and flight tests (invited) |date=2000 |last1=Marcucci |first1=M. G. |last2=Polk |first2=J. E. |journal=Review of Scientific Instruments |volume=71 |pages=1389–1400 |bibcode=2000RScI...71.1389M |issue=3}}</ref><ref>{{cite web |url=http://gltrs.grc.nasa.gov/reports/1999/TM-1999-209439.pdf |title=A Synopsis of Ion Propulsion Development Projects in the United States: SERT I to Deep Space I |first1=James S. |last1=Sovey |first2=Vincent K. |last2=Rawlin |first3=Michael J. |last3=Patterson |publisher=NASA |access-date=12 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090629225625/http://gltrs.grc.nasa.gov/reports/1999/TM-1999-209439.pdf |archive-date=29 June 2009}}</ref> Nevertheless, [[field-emission electric propulsion]] thrusters that accelerate liquid metal ions such as caesium have been built.<ref>{{cite conference |url=http://trs-new.jpl.nasa.gov/dspace/handle/2014/11649 |title=In-FEEP Thruster Ion Beam Neutralization with Thermionic and Field Emission Cathodes |format=PDF |access-date=25 January 2010 |conference=27th International Electric Propulsion Conference |place=Pasadena, California |date=October 2001 |pages=1–15 |author=Marrese, C. |author2=Polk, J. |author3=Mueller, J. |author4=Owens, A. |author5=Tajmar, M. |author6=Fink, R. |author7=Spindt, C. |name-list-style=amp |url-status=dead |archive-url=https://web.archive.org/web/20100527071653/http://trs-new.jpl.nasa.gov/dspace/handle/2014/11649 |archive-date=27 May 2010}}</ref>

[[Caesium nitrate]] is used as an [[oxidizing agent|oxidizer]] and [[pyrotechnic colorant]] to burn [[silicon]] in [[infrared]] [[flare (pyrotechnic)|flares]],<ref>{{cite web |url=http://www.freepatentsonline.com/6230628.html |work=United States Patent 6230628 |title=Infrared illumination compositions and articles containing the same |publisher=Freepatentsonline.com |access-date=25 January 2010 |archive-date=8 July 2021 |archive-url=https://web.archive.org/web/20210708104649/https://www.freepatentsonline.com/6230628.html |url-status=live }}</ref> such as the LUU-19 flare,<ref>{{cite web |url=https://fas.org/man/dod-101/sys/dumb/luu19.htm |title=LUU-19 Flare |publisher=Federation of American Scientists |date=23 April 2000 |access-date=12 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100806093502/http://www.fas.org/man/dod-101/sys/dumb/luu19.htm |archive-date=6 August 2010}}</ref> because it emits much of its light in the [[infrared|near infrared]] spectrum.<ref>{{cite journal |doi=10.1016/j.tca.2006.04.002 |title=Determination of the temperature and enthalpy of the solid–solid phase transition of caesium nitrate by differential scanning calorimetry |date=2006 |last1=Charrier |first1=E. |first2=E. L. |first3=P. G. |first4=H. M. |first5=B. |first6=T. T. |journal=Thermochimica Acta |volume=445 |pages=36–39 |last2=Charsley |last3=Laye |last4=Markham |last5=Berger |last6=Griffiths|issue=1 |bibcode=2006TcAc..445...36C }}</ref> Caesium compounds may have been used as fuel additives to reduce the [[radar cross-section|radar signature]] of [[exhaust gas|exhaust plumes]] in the [[Lockheed A-12]] [[CIA]] reconnaissance aircraft.<ref>{{cite book |isbn=978-1-84176-098-8 |page=47 |title=Lockheed SR-71: the secret missions exposed |last=Crickmore |first=Paul F. |publisher=Osprey |date=2000}}</ref> Caesium and rubidium have been added as a [[carbonate]] to glass because they reduce electrical conductivity and improve stability and durability of [[optical fiber|fibre optics]] and [[night vision]] devices. Caesium fluoride or caesium aluminium fluoride are used in fluxes formulated for brazing [[aluminium]] alloys that contain [[magnesium]].<ref name="USGS"/>

[[MHD generator|Magnetohydrodynamic (MHD) power]]-generating systems were researched, but failed to gain widespread acceptance.<ref>{{cite book |author=National Research Council (U.S.) |publisher=National Academy Press |date=2001 |title=Energy research at DOE—Was it worth it? |access-date=26 September 2010 |url=http://books.nap.edu/openbook.php?isbn=0309074487&page=52 |isbn=978-0-309-07448-3 |pages=190–194 |doi=10.17226/10165 |archive-date=23 March 2016 |archive-url=https://web.archive.org/web/20160323154247/http://www.nap.edu/read/10165/chapter/1 |url-status=live }}</ref> Caesium metal has also been considered as the working fluid in high-temperature [[Rankine cycle]] turboelectric generators.<ref>{{cite book |title=Economics of Caesium and Rubidium (Reports on Metals & Minerals) |publisher=Roskill Information Services |date=1984 |place=London, United Kingdom |author=Roskill Information Services |page=51 |isbn=978-0-86214-250-6}}</ref>

Caesium salts have been evaluated as antishock reagents following the administration of [[arsenic toxicity|arsenical drugs]]. Because of their effect on heart rhythms, however, they are less likely to be used than potassium or rubidium salts. They have also been used to treat [[epilepsy]].<ref name="USGS"/>

Caesium-133 can be [[laser cooling|laser cooled]] and used to probe fundamental and [[Quantum technology|technological]] problems in [[quantum mechanics|quantum physics]]. It has a particularly convenient [[Feshbach resonance|Feshbach]] spectrum to enable studies of [[ultracold atom]]s requiring tunable interactions.<ref>{{cite journal |last1=Chin |first1=Cheng |last2=Grimm |first2=Rudolf |last3=Julienne |first3=Paul |last4=Tiesinga |first4=Eite |date=29 April 2010 |title=Feshbach resonances in ultracold gases |journal=Reviews of Modern Physics |volume=82 |issue=2 |pages=1225–1286 |doi=10.1103/RevModPhys.82.1225 |arxiv=0812.1496 |bibcode=2010RvMP...82.1225C |s2cid=118340314}}</ref>