A History Of Cesium

Posted on by Brian Colwell

Cesium, the soft silvery-gold metal that melts in your hand and explodes on contact with water, has emerged from its discovery in German mineral springs to become one of the most critical elements in modern technology. This highly reactive alkali metal, whose name derives from the Latin word for “sky blue,” has played pivotal roles in advancing atomic timekeeping, petroleum exploration, cancer treatment, and nuclear science. From its spectroscopic discovery by Bunsen and Kirchhoff in 1860 to its current applications in everything from atomic clocks that define our second to life-saving medical treatments, cesium’s journey reflects humanity’s evolving mastery of the elements and their practical applications in solving complex technological challenges.

Find out more about cesium here. Be sure to check out all other critical raw materials (CRMs), as well.

A History Of Cesium

The history of cesium spans over 160 years, beginning with its groundbreaking discovery through the newly invented spectroscope and evolving into applications that underpin modern technology, from the precise measurement of time to advanced medical treatments and deep-sea oil drilling. This chronology traces cesium’s transformation from a scientific curiosity identified by its distinctive blue spectral lines to an essential element in numerous critical technologies.

Chronology

  • 1846 – Carl Plattner analyzed pollucite mineral, found only 93% of its composition, and missed the cesium content, mistaking it for sodium and potassium [1, 2, 3]
  • 1860 – Robert Bunsen and Gustav Kirchhoff discovered cesium in mineral water from Dürkheim, Germany, using spectroscopy, naming it after the Latin word “caesius” meaning “sky blue”; cesium became the first element discovered by spectroscopy; they evaporated 44,000 litres of mineral water to obtain seven grams of cesium chloride [4, 5, 1, 6, 7, 8, 2, 3, 9]
  • 1861 – Bunsen and Kirchhoff estimated cesium’s atomic weight at 123.35 from cesium chloride; attempted to isolate elemental cesium by electrolysis but obtained only a blue substance [4, 10, 1]
  • 1864 – Second analysis of pollucite revealed the high cesium content missed by Plattner in 1846 [10]
  • 1882 – Carl Setterberg published his work and successfully isolated pure cesium metal by electrolysis of cesium cyanide; determined cesium’s melting point as 26-27°C and density as 1.88 g/cm³ [4, 8, 2, 4, 12, 11]
  • 1910s – Cesium compounds began use in photoelectric cells due to cesium’s low work function [5]
  • 1920s – First practical applications of cesium realized, including use in vacuum tubes as oxygen getter and cathode coating; mining began at Bernic Lake cesium-bearing pegmatite [5, 13, 5]
  • 1930 – The Tanco pegmatite at Bernic Lake discovered, containing major cesium deposits [14]
  • 1949 – Optical pumping technique developed for cesium atom energy level transitions [15]
  • 1950 – Ramsey interferometry technique applied to cesium beam spectroscopy [15]
  • 1954 – Tanco mine opened at cesium-bearing pegmatite [14]
  • 1955 – Louis Essen built first cesium atomic clock at National Physical Laboratory, UK [16, 15]
  • 1956 – First commercial cesium atomic clock “Atomichron” sold for $50,000 [17, 15]
  • 1960 – Second defined based on cesium-133 transitions; Tanco mine closed temporarily [16, 14]
  • 1967 – Second officially redefined as 9,192,631,770 periods of cesium-133 radiation; Tanco reopened for cesium production [16, 18, 19, 14]
  • 1971 – Cesium-137 radiotherapy unit installed in Brazil with 74 terabecquerels activity [20]
  • 1977 – IGR purchased cesium-137 radiotherapy unit [20]
  • 1978 – Study published on cesium-bearing pollucite alteration in Manitoba [21]
  • 1980 – Cesium compounds began use as catalysts in polyurethane foam production [22]
  • 1982 – Tanco cesium mine closed temporarily [14]
  • 1985 – Cesium-137 radiotherapy unit abandoned by IGR; Tanco cesium ore body measured at 1,400m × 600m × 100m [23, 20, 14]
  • 1986 – Chernobyl accident released cesium-137 across Europe, 2000-4000 Bq/m² in Germany [24]
  • 1987 – Goiânia cesium-137 accident killed 4 and contaminated 249 people [24, 23, 20, 25]
  • 1990 – Shell Research developed cesium formate brine for high-temperature drilling [26]
  • 1991 – Cesium fluoride-mediated synthesis of heterocycles reported [27]
  • 1993 – Cabot Corporation purchased Tanco cesium mine [28, 14]
  • 1994 – Cesium formate became largest application of cesium for drilling fluids [26, 4]
  • 1996 – Cabot began cesium formate production from pollucite at Tanco [28, 14, 29]
  • 1997 – BIPM specified cesium second definition at 0 K; cesium formate drilling studies published [16, 30]
  • 1998 – Acerinox accidentally melted cesium-137 from gamma ray generator [31]
  • 1999 – Cesium formate used in over 120 North Sea wells; cesium fluoride catalysis studies published [32, 33]
  • 2000 – Court ordered R$1.3 million compensation for Goiânia cesium accident [20]
  • 2003 – Cesium-131 FDA approved for permanent seed implants [34]
  • 2008 – Cesium formate brine used at record 437°F/225°C in Hungary [32]
  • 2009 – Pure cesium priced at $10 per gram [4]
  • 2010 – Cesium-131 brachytherapy clinical trials for head and neck cancers [35]
  • 2011 – Fukushima released cesium-137 contaminating Japanese soils [24, 36, 37]
  • 2013 – JILA achieved evaporative cooling with cesium hydroxide molecules [38, 39]
  • 2016 – Cesium-131 brachytherapy studies confirmed brain metastases treatment efficacy [5, 40]
  • 2018 – BIPM restated cesium second definition with fixed numerical value [16]
  • 2019 – Sinomine purchased Tanco cesium mine for $135 million; cesium-131 prostate studies published [28, 41, 15, 42]
  • 2020 – Cesium-131 prostate brachytherapy showed excellent biochemical control [43]
  • 2023 – Sinomine proposed draining Bernic Lake for cesium open-pit mining [41]
  • 2024 – Cesium market valued at $363.58 million [44]
  • 2025 – NIST-F4 cesium fountain clock activated, accurate to 1 second in 100 million years [45]
  • 2030 – Expected redefinition of second from cesium to optical clocks [15]

Final Thoughts

Cesium’s remarkable journey from its spectroscopic discovery to its current status as a critical element exemplifies the unpredictable paths of scientific progress. What began as mysterious blue lines in a spectroscope has evolved into applications that touch nearly every aspect of modern life – from the GPS satellites that guide us to the medical treatments that heal us. The element’s unique properties, once merely scientific curiosities, now enable technologies that would have seemed impossible to Bunsen and Kirchhoff.

As we look toward the future, with optical clocks promising even greater precision and new medical applications emerging, cesium continues to demonstrate that fundamental scientific discoveries, pursued for knowledge alone, often yield the most transformative practical benefits for humanity.

Thanks for reading!

References

[1] Cesium Element Facts – https://www.chemicool.com/elements/cesium.html

[2] Cesium Facts, Symbol, Discovery, Properties, Uses – https://www.chemistrylearner.com/cesium.html

[3] Caesium – Element information, properties and uses | Periodic Table – https://periodic-table.rsc.org/element/55/caesium

[4] Caesium – Wikipedia – https://en.wikipedia.org/wiki/Caesium

[5] Facts About Cesium | Live Science – https://www.livescience.com/37578-cesium.html

[6] Cesium | Description, Symbol, Uses, & Facts | Britannica – https://www.britannica.com/science/cesium

[7] It’s Elemental – The Element Cesium – https://education.jlab.org/itselemental/ele055.html

[8] Caesium | Cesium History, Uses, Facts, Physical & Chemical Characteristics – https://periodic-table.com/caesium/

[9] The Spontaneous Element Cesium | Periodic Table | ChemTalk – https://chemistrytalk.org/cesium-element/

[10] Pollucite – Wikipedia – https://en.wikipedia.org/wiki/Pollucite

[11] Look who discovered caesium… | Feature | RSC Education – https://edu.rsc.org/feature/look-who-discovered-caesium-/2020183.article

[12] Atomic Weight of Caesium | Commission on Isotopic Abundances and Atomic Weights – https://ciaaw.org/caesium.htm

[13] Tancomine | Manitoba | Oil & Gas | Canada – https://tancomine.com/about/

[14] Tanco Mine, Bernic Lake, Lac-du-Bonnet area, Manitoba, Canada – https://www.mindat.org/loc-505.html

[15] Atomic clock – Wikipedia – https://en.wikipedia.org/wiki/Atomic_clock

[16] Caesium standard – Wikipedia – https://en.wikipedia.org/wiki/Caesium_standard

[17] Beams of Atoms: The First Atomic Clocks | NIST – https://www.nist.gov/atomic-clocks/beams-atoms-first-atomic-clocks

[18] Atomic clock | Timekeeping, Accuracy & Benefits | Britannica – https://www.britannica.com/technology/atomic-clock

[19] Quantum mechanics – Cesium Clock, Timekeeping, Accuracy | Britannica – https://www.britannica.com/science/quantum-mechanics-physics/Cesium-clock

[20] Goiânia accident – Wikipedia – https://en.wikipedia.org/wiki/Goi%C3%A2nia_accident

[21] Pollucite: Mineral information, data and localities. – https://www.mindat.org/min-3255.html

[22] Cesium hydroxide | 21351-79-1 – https://www.chemicalbook.com/ChemicalProductProperty_EN_CB7357929.htm

[23] Hundreds are accidentally poisoned in Brazil – https://www.history.com/this-day-in-history/september-18/accidental-poisoning-in-brazil

[24] Caesium-137 – Wikipedia – https://en.wikipedia.org/wiki/Caesium-137

[25] The Goiânia Incident: Lessons from a Radiological Disaster | Argon Electronics – https://www.argonelectronics.com/blog/goiania-incident-radiological-safety-lessons

[26] Use of formate-based fluids for drilling and completion | Offshore – https://www.offshore-mag.com/business-briefs/equipment-engineering/article/16759488/use-of-formate-based-fluids-for-drilling-and-completion

[27] Cesium Fluoride – an overview | ScienceDirect Topics – https://www.sciencedirect.com/topics/chemistry/cesium-fluoride

[28] Tanco Mine – Wikipedia – https://en.wikipedia.org/wiki/Tanco_Mine

[29] Cesium Formate – The Beneficial Effects of Low Viscosity and High Initial Fluid Loss on Drilling Rate – A Comparative Experiment – OnePetro – https://www.onepetro.org/conference-paper/SPE-36398-MS

[30] Cesium Formate Fluids – https://www.oilandgasonline.com/doc/cesium-formate-fluids-0001

[31] Special Report: Australia’s Cesium 137 Accident – A Radioactive Nightm – MIRA Safety – https://www.mirasafety.com/blogs/news/radioactive-isotope

[32] Cabot Specialty Fluids’ Cesium Formate Brine Sets New Record in 437 Degrees F/225 Degrees C Well Kill and Suspension Operation | Cabot Corporation – https://investor.cabot-corp.com/news-releases/news-release-details/cabot-specialty-fluids-cesium-formate-brine-sets-new-record-437

[33] Cesium Fluoride Catalyzed Trifluoromethylation of Esters, Aldehydes, and Ketones with (Trifluoromethyl)trimethylsilane | The Journal of Organic Chemistry – https://pubs.acs.org/doi/10.1021/jo982494c

[34] Cesium 131 – an overview | ScienceDirect Topics – https://www.sciencedirect.com/topics/medicine-and-dentistry/cesium-131

[35] Cesium-131 brachytherapy in high risk and recurrent head and neck cancers: first report of long-term outcomes – PMC – https://pmc.ncbi.nlm.nih.gov/articles/PMC4716131/

[36] External Cesium-137 doses to humans from soil influenced by the Fukushima and Chernobyl nuclear power plants accidents: a comparative study | Scientific Reports – https://www.nature.com/articles/s41598-020-64812-9

[37] Cesium-137 deposition and contamination of Japanese soils due to the Fukushima nuclear accident | PNAS – https://www.pnas.org/doi/10.1073/pnas.1112058108

[38] Cesium Hydroxide Solution | AMERICAN ELEMENTS ® – https://www.americanelements.com/cesium-hydroxide-solution-21351-79-1

[39] Cesium Hydroxide Hydrate | AMERICAN ELEMENTS® – https://www.americanelements.com/cesium-hydroxide-hydrate-12260-45-6

[40] Cesium-131 brachytherapy for the treatment of brain metastases: Current status and future perspectives – PubMed – https://pubmed.ncbi.nlm.nih.gov/36753799/

[41] Chinese owner of Manitoba mine wants to drain lake to extract more cesium from one of world’s few deposits | CBC News – https://www.cbc.ca/news/canada/manitoba/sinomine-tanco-expansion-manitoba-1.6897808

[42] Long-term biochemical outcomes using cesium-131 in prostate brachytherapy – PubMed – https://pubmed.ncbi.nlm.nih.gov/31427178/

[43] Cesium-131 prostate brachytherapy: A single institutional long-term experience – PubMed – https://pubmed.ncbi.nlm.nih.gov/32249178/

[44] Cesium Market: Global Industry Analysis and Forecast (2025-2032) – https://www.maximizemarketresearch.com/market-report/global-cesium-market/89395/

[45] NIST set its new atomic clock in motion, and it’s astoundingly precise – The Washington Post – https://www.washingtonpost.com/science/2025/05/17/nist-atomic-clock-time-cesium/