Krypton is a chemical element with symbol Kr and atomic number 36. Krypton is a colorless, odorless, tasteless gas. It was discovered by the Scottish chemist Sir William Ramsey in 1898. He discovered a series of noble gases by examining the residue left over from evaporating liquefied air.
Krypton is one of the noble gases in Group 18 of the periodic table along with helium, neon, argon, xenon and radon. Because their outer shell of electrons is full, the nobles gases are very non-reactive and form few compounds with other elements. The melting point and boiling point of krypton are very close at -157° C and -153° C.
Krypton has 33 known isotopes that vary in atomic weight from 69 to 101. There are 6 stable isotopes and 27 radioactive isotopes.. Kr-83,84,85,and 86 are fission products produced by uranium decay. Small amounts of some krypton isotopes are generated by cosmic rays hitting the atmosphere. The radioisotopes have half-lives that vary from 154 billionths of a second for Kr-83m1 to 225,000 years for Kr-81. Most of the isotopes of krypton are short lived The primary decay mode of isotopes lighter than atomic weight 82 is emission of a positron (anti-electron) to become bromine. Above atomic weight 84, krypton decay emits an electron to become rubidium. Kr-71 and Kr-73 emit protons is a small number of decays and become selenium. Metastable states of Kr-83 and Kr-85 emit gamma rays when they decay. A few krypton isotopes emit gamma rays when they decay. Kr-92, Kr-93, Kr-94, Kr-97 and Kr-101 emit neutrons during decay.
Krypton is present on Earth mainly as a minor constituent of the atmosphere. It is also present in gas emitted from underwater thermal vents and from volcanoes. Krypton is the second rarest stable element on Earth.
Krypton is used to make bright white lights for photography. Powerful lasers have been developed utilizing krypton. Krypton-81 can be used to date old groundwater up to 800,000 years old. Krypton-83 is used in magnetic resonance imaging of respiratory system. It may also be useful in computer tomography imaging in a mixture of gases including xenon. Krypton-85 with a half-life of about 10 years is used indicator lights in home appliances and consumer electronics, to gauge thickness of plastics, sheet metal, rubber and paper, to measure dust and pollutant levels, to detect explosives, in voltage regulators and surge protectors, and in laboratory gas chromatography equipment. Kr-85 is released when nuclear fuel rods are reprocessed and can be used to detect clandestine reprocessing plants.
Krypton has no known biological function and is considered harmless with regard to health. Krypton could cause asphyxiation if present in sufficient quantities to displace oxygen in the air being breathed. The radioisotopes are very short lived and their beta emission are easily blocked.
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