cézium

Cesium, with the chemical symbol Cs and atomic number 55, is a soft, silvery-gold alkali metal with a melting point of 28.5 degrees Celsius. It is the most electropositive and least dense of the stable alkali metals, and it is the least reactive of the stable alkali metals. Cesium is highly reactive with air and water, and it reacts vigorously with halogens to form salts. It is also known for its ability to give off a blue-violet light when exposed to air, due to the formation of cesium oxide.

Cesium is primarily obtained from the mineral pollucite, which is a type of zeolite. It is also found in small amounts in other minerals, such as beryl and avogadrite. Cesium has a number of applications in industry and science. It is used in atomic clocks, which are used to keep precise time, and in ion propulsion systems for spacecraft. It is also used in the production of certain types of glass, and in the manufacture of photocells and infrared detectors.

Cesium has a number of isotopes, with the most stable being cesium-133, which has a half-life of over 100 billion years. Cesium-137, which has a half-life of about 30 years, is a radioactive isotope that is produced as a byproduct of nuclear fission. It is a significant contributor to the radioactivity of nuclear waste, and it is also used in the treatment of certain types of cancer.

Cesium is a toxic substance, and it should be handled with care. It can cause skin irritation and burns, and it can also cause damage to the liver and kidneys if ingested. It is also a potent neurotoxin, and it can cause seizures and coma if inhaled or injected. Cesium is not known to have any biological role in humans or other animals.