Caesium
Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is one of the alkali metals, a group that includes lithium, sodium, potassium, rubidium, and francium. It is characterized by its soft, silvery-golden appearance and is one of the most electropositive elements.
Physical and Chemical Properties
Caesium is notable for its low melting point of 28.5 °C (83.3 °F), making it one of the few metals that is liquid at or near room temperature. Its softness and high reactivity require that it be stored and handled carefully, often under an inert gas atmosphere to prevent it from reacting with air or moisture.
Isotopes
Caesium has 41 known isotopes, with mass numbers ranging from 112 to 152. Of these, only caesium-133 is stable and naturally occurring. The isotope caesium-137 is a notable radioactive isotope that is a common fission product in nuclear reactors and has applications in various fields including medical radiotherapy.
Applications
Atomic Clocks
Caesium is perhaps best known for its role in atomic clocks. The caesium standard is used to define the second in the International System of Units. This is based on the transition frequency between two hyperfine levels of the ground state of the caesium-133 atom.
Industry and Technology
In the industrial sector, caesium is used in the manufacturing of photoelectric cells, photomultiplier tubes, and other optical components for infrared spectrophotometry. Its photoemissive properties make it useful in devices that convert light to electron flow. Caesium is also used as a catalyst in organic reactions and in the production of scintillation counters.
Nuclear and Medical Uses
Caesium fluoride (CsF) is employed in organofluorine chemistry as a source of fluoride anions. In nuclear medicine, caesium-137 is used in cancer treatment through brachytherapy.
Energy Sector
Caesium is used in magnetohydrodynamic power generators and in two-electrode vacuum tube converters, where it enhances current flow by neutralizing space charge near the cathode.
Caesium Compounds
Caesium chloride and caesium oxide are compounds of caesium utilized for various applications. Caesium chloride is often used as a source of caesium ions in chemical syntheses, while caesium oxide serves in the preparation of various caesium salts.
Safety and Handling
Due to its reactivity, particularly with water, caesium must be handled with care, often stored under oil or inert gas, such as argon, to prevent accidental ignition or explosion.