Krypton

History

(Gr. kryptos: hidden) Discovered in 1898 by Ramsay and Travers in the residue left after liquid air had nearly boiled away. In 1960 it was internationally agreed that the fundamental unit of length, the meter, should be defined in terms of the orange-red spectral line of ⁸⁶Kr. This replaced the standard meter of Paris, which was defined in terms of a bar made of a platinum-iridium alloy. In October 1983, the meter, which originally was defined as being one ten millionth of a quadrant of the earth's polar circumference, was again redefined by the International Bureau of Weights and Measures as being the length of a path traveled by light in a vacuum during a time interval of 1/299,792,458 of a second.

Properties

Krypton is a "noble" gas due to its very low chemical reactivity. It is colorless and it is characterized by its brilliant green and orange spectral lines. It is one of the products of uranium fission. Solidified krypton is white and crystalline with a face-centered cubic crystal structure, which is a common property of all "rare gases."

While krypton is generally thought of as a rare gas that normally does not combine with other elements to form compounds, it now appears that the existence of some krypton compounds can exist. Krypton difluoride has been prepared in gram quantities and can be made by several methods. A higher fluoride of krypton and a salt of an oxyacid of krypton also have been reported. Molecule-ions of ArKr+ and KrH+ have been identified and investigated, and evidence is provided for the formation of KrXe or KrXe+.

Sources

Krypton is present in the air to the extent of about 1 ppm. The atmosphere of Mars has been found to contain 0.3 ppm of krypton. Solid krypton is a white crystalline substance with a face-centered cubic structure which is common to all the "rare gases." It can be extracted from liquid air by fractional distillation.

Uses

Krypton clathrates are prepared using hydroquinone and phenol. ⁸⁵Kr can be used for chemical analysis by imbedding the isotope in various solids. During this process, kryptonates are formed.  Kryptonate activity is sensitive to chemical reactions at the solution surface. Estimates of the concentration of reactants are therefore made possible. Krypton is used in certain photographic flash lamps for high-speed photography. Uses thus far have been limited because of its high cost, as Krypton gas presently costs about $30/l.

Isotopes

Naturally occurring krypton contains six stable isotopes. Seventeen other unstable isotopes are recognized. The spectral lines of krypton are easily produced and some are very sharp. Kr-81 is the product of atmospheric reactions with the other naturally occurring isotopes of krypton. It is radioactive with a half-life of 250,000 years. Like xenon, krypton is highly volatile when it is near surface waters and Kr-81 has therefore been used for dating old groundwater. Kr-85 is an inert radioactive noble gas with a half-life of 10.76 years, that is produced by fission of uranium and plutonium. Sources have included nuclear bomb testing, nuclear reactors, and the release of Kr-85 during the reprocessing of fuel rods from nuclear reactors.

Hazards

Krypton is a non-toxic simple asphyxiant. High concentrations may exclude an adequate supply of oxygen to the lungs. Effect of oxygen deficiency resulting from simple asphyxiants may include: rapid breathing, diminished mental alertness, impaired muscular coordination, faulty judgement, depression of all sensations, emotional instability, and fatigue. As asphyxiation progresses, nausea, vomiting, prostration, and loss of consciousness may result, eventually leading to convulsions, coma, and death.