This element is no longer available.
Krypton is present in the air at about 1 ppm. The atmosphere of Mars contains a little (about 0.3 ppm) of krypton. It is characterised by its brilliant green and orange spectral lines. The spectral lines of krypton are easily produced and some are very sharp. In 1960 it was internationally agreed that the fundamental unit of length, the metre, should be defined as 1 m = 1,650,763.73 wavelengths (in vacuo) of the orange-red line of Kr-33.
Under normal conditions krypton is colourless, odourless, fairly expensive gas. Solid krypton is a white crystalline substance with a face-centred cubic structure which is common to all the “rare gases”. Krypton difluoride, KrF2, has been prepared in gram quantities and can be made by several methods. Other compounds are unstable, unless isolated in a matrix at very low temperatures.
Krypton is used to fill electric lamp bulbs which are filled with a mixture of krypton and argon, and for various electronic devices. Krypton is also used in photographic projection lamps, in very high-powered electric arc lights used at airports and in some strobe-lamps, because it has an extremely fast response to an electric current.
A mixture of stable and unstable isotopes of krypton is produced by slow neutron fission of uranium in nuclear reactors as Kripron-85, its most stable isotope. It is used to detect leaks in sealed containers, to excite phosphors in light sources with no external source of energy, and in medicine to detect abnormal heart openings.