Caesium: a metal used to check clocks

The first element discovered by spectral analysis

This el­e­ment is a soft, sil­very-gold met­al with a low melt­ing tem­per­a­ture - 28.7°С (I.e. a lit­tle over room tem­per­a­ture).

The re­ac­tive abil­i­ty of the el­e­ments in the group in­creas­es from top to bot­tom. Cae­sium is at the bot­tom of the first group, and is very re­ac­tive. If you throw a lit­tle cae­sium into wa­ter, a pow­er­ful ex­plo­sion takes place, and the met­al burns quick­ly in air. It is only pos­si­ble to work with it in an in­ert at­mos­phere, and it must be stored un­der a lay­er of oil, or in sealed cap­sules. Cae­sium has two ra­dioac­tive iso­topes – Cs-134 and Cs-137.

Oc­cur­rence of cae­sium

Cae­sium re­ceived its name from the Latin word cae­sius, “sky-blue”. Cae­sium is con­tained in the rare min­er­al pol­lu­cite. Its de­posits are main­ly found in Cana­da, and also in Namib­ia, Zim­bab­we, Rus­sia (Kola Penin­su­la, East­ern Sayan, Trans­baikal re­gion). Small, eco­nom­i­cal­ly in­signif­i­cant de­posits of pol­lu­cite are also found in Kaza­khstan, Mon­go­lia and Italy. Around 20 tons of en­riched cae­sium ore is pro­duced world­wide an­nu­al­ly. The an­nu­al vol­ume of pro­duc­tion of the pure met­al is around 9 tons. The de­mand for cae­sium is con­stant­ly grow­ing, and ex­ceeds the vol­umes of its pro­duc­tion. So the sit­u­a­tion of the cae­sium mar­ket is high­ly pre­car­i­ous, just as it is with tan­ta­lum and rhe­ni­um.

How cae­sium was dis­cov­ered

In 1860, the Ger­man sci­en­tists Robert Wil­helm Bun­sen and Gus­tav Robert Kirch­hof were study­ing the wa­ters of the Bad Dürkheim min­er­al spring by the method of op­tic spec­troscopy. They de­tect­ed two new blue lines in the spec­trum. Thus, cae­sium be­came the first el­e­ment to be dis­cov­ered by spec­tral anal­y­sis! In 1882, the Swedish chemist Carl Set­ter­berg con­duct­ed elec­trol­y­sis of an al­loy of cae­sium cyanide and bar­i­um and ex­tract­ed cae­sium in pure form.


Cae­sium-137 has a half-life of 30 years. This in­fa­mous iso­tope was present in ra­dioac­tive waste from un­der­ground nu­cle­ar test­ing (1945-1963), and also in the fall­out from the Cher­nobyl dis­as­ter. Large quan­ti­ties of Cs-137 were de­tect­ed from East­ern Eu­rope to Ire­land. It af­fect­ed plants and live­stock graz­ing on con­tam­i­nat­ed lands. The use of these ar­eas was high­ly re­strict­ed, and plants and an­i­mals were test­ed for con­tam­i­na­tion. Traces of the iso­tope were still de­tect­ed even 25 years af­ter the dis­as­ter.

Ar­eas were also con­tam­i­nat­ed by Cs-137 in Japan af­ter the dis­as­ter at the nu­cle­ar en­er­gy plant in Fukushi­ma in 2011. For­tu­nate­ly, ac­cord­ing to nu­mer­ous re­searchers, the ra­dioac­tive par­ti­cles set­tled in pro­cessed fuel, and were not car­ried away with the smoke, stop­ping them from spread­ing too far.

Cae­sium is a mi­croele­ment con­tained in plants and the or­gan­isms of an­i­mals (main­ly in the mus­cles, heart, liv­er and blood). Ra­dioac­tive Cs-137 ac­cu­mu­lates in fresh­wa­ter al­gae, arc­tic plants and lichens. A rel­a­tive­ly high ac­cu­mu­la­tion ra­tio is not­ed in rein­deer and North Amer­i­can wa­ter birds. The fol­low­ing mush­rooms are also con­sid­ered to be “ac­cu­mu­la­tors” of ra­dioac­tive cae­sium: yel­low bo­le­tus, bo­le­tus, pax­il, wool­ly milk­cap and bay bo­lete. But the bi­o­log­i­cal role of cae­sium is still not ful­ly un­der­stood.


The sta­ble iso­tope Cs-133 is used in pho­toele­ments, pho­to­mul­ti­pli­ers and de­tec­tors of ion­iz­ing ra­di­a­tion (cae­sium io­dide). Cs-133 is also used as an op­ti­cal ma­te­ri­al (in the form of io­dide and bro­mide), and in the man­u­fac­ture of lu­mi­nous tubes (in com­bi­na­tions with zir­co­ni­um and tin). Cae­sium acts as a cat­a­lyst in the pro­duc­tion of am­mo­ni­um, sul­fu­ric acid, butyl al­co­hol, in de­hy­dro­g­e­niza­tion re­ac­tions and in the pro­duc­tion of formic acid. Cae­sium is the ba­sis of med­i­cal prod­ucts for the treat­ment of ul­cer­ous dis­eases, diph­the­ria, shocks and schizophre­nia. Cae­sium plas­ma is a com­po­nent of MHD-gen­er­a­tors with high pow­er ef­fi­cien­cy.

Cs-133 is used in atom­ic clocks – the most pre­cise de­vices for telling the time. Since 1967, in the SI in­ter­na­tion­al sys­tem of units, 1 sec­ond has been de­fined as 9 192 631 770 pe­ri­ods of the ra­di­a­tion cor­re­spond­ing to the tran­si­tion be­tween the two hy­per­fine lev­els of the ground state of the cae­sium-133 atom. The first cae­sium atom­ic clock was built in 1955 by Louis Es­sen at the Na­tion­al Physics Lab­o­ra­to­ry in the UK. This clock has an ac­cu­ra­cy of one sec­ond in 300,000 years. To­day, atom­ic clocks are used in the nav­i­ga­tion sys­tems of space­craft, satel­lites, bal­lis­tic rock­ets, air­craft, sub­marines and au­to­mo­biles func­tion­ing au­to­mat­i­cal­ly by satel­lite link. Atom­ic clocks are also used in sys­tems of satel­lite and ground telecom­mu­ni­ca­tions, in mo­bile base sta­tions, in­ter­na­tion­al and na­tion­al stan­dards of­fices and ser­vices of ex­act time.