The Probert Encyclopaedia of Science & Technology

KRYPTON

Krypton, named from the Greek word kryptos, meaning 'hidden', is an odourless, colourless, tasteless, non-toxic, monatomic, and highly stable gaseous element of the noble gases group with the symbol Kr. The concentration of Krypton gas in the atmosphere by volume is 1.1 x 10-4. Traces of krypton are present in minerals and meteorites, but the usual commercial source is the atmosphere, which contains 1.14 parts per 106 by volume. Krypton also is formed by the nuclear fission of uranium triggered by slow neutrons: this source may be expected to become increasingly important because of the growing number of fission-power plants.

Krypton has isotopes of every mass number from 74 through 95; six, with mass numbers 78, 80, 82, 83, 84, and 86, are stable. After it has been stored a few days, krypton obtained by nuclear fission contains only one radioactive isotope, krypton-85, which has a half-life of about 10 years, because all the other radioactive isotopes have half-lives of three hours or less. Because its boiling point is about 30 degrees C higher than those of the major constituents of air,
krypton is readily separated from liquid air by fractional distillation; it accumulates along with xenon in the least volatile portion. These two gases are further purified by adsorption onto silica gel, redistillation, and passage over hot titanium metal, which removes all impurities except other noble gases.

Krypton gas liquefies at -152.30 degrees C and freezes 4 degrees C lower. When a current of electricity is passed through a glass tube containing krypton at low pressure, a bluish white light is emitted. The wavelength of an orange-red component of light emitted by stable
krypton-86, because of its extreme sharpness, served as the international standard for the metre from 1960 to 1983. (One metre equals 1,650,763.73 times the wavelength of this line).
Krypton gas is principally shipped and used in gaseous form for excimer lasers, light bulbs, window insulation and Research and Development laboratory research.
Research Krypton