Krypton

=Krypton=

Basic Facts
Krypton (Kr) has the atomic number 36 and can be found in group 18 of the periodic table. It is one of the noble gases and is dense, odorless, tasteless, and colorless. It is often used for lighting and photography. Krypton is used primarily in gas discharge lamps and fluorescent lamps. Krypton has a large number of high spectral lines which allows it to be harnessed into high intensity lasers. Krypton is a product of uranium fission. Krypton's atmospheric concentration is about 1 ppm. Krypton is also Superman's home planet.

History
Was discovered in Britain in 1898 by Sir William Ramsay, a scottish chemist and an english chemist, Morris Travers. William Ramsey was awarded the Nobel Prize in Chemistry for his discovery. In 190l an international agreement finally determined and defined the meter in terms of wavelength of light emmited by the krypton-86 isotope.

Characteristics
Krypton is characterized by several sharp emission lines, the strongest of which is green and yellow. Krypton is considered to be one of the few products of a uranium fission reaction. Krypton can also be found as a solid, which is a white and crystalized solid with a face-centered cubic crystal structure, which is found to be common among other noble gasses.

It is known to form very few compounds, one being Krypton difluoride. Not only is it used for lights but also luminous signs that glow with a green-yellowish light.


 * Uses**
 * used with argon as a low-pressure filling gas for fluorescent lights
 * used in some photographic flash lamps for high-speed photography, lamps, UV-laser spectral line used for international measurement of a metre

The fractional and independent fission yields of krypton isotopes (masses 87 to 94) and xenon isotopes (masses 137-143) produced in thermal-neutron fission of 235 Uwere measured using a mass separator operating in an on-line mode with a fission source exposed to time-controlled neutron fluxes. The noble-gas isotopes were collected simultaneously at given times and each mass was measured separately. The distribution of the isotopic yields of each element was found to be Gaussian, in general agreement with Wahl's estimates. The total independent yields of krypton and xenon, as well as their complementary elements, barium and strontium, were found to indicate an odd-even effect in the element yield distribution. Even-Z elements are formed in higher yields than their odd-Z neighbors (20-50% higher); the even-Z yields are also higher than Wahl's "normal" element yields (∼12% higher for Kr and Ba and ∼40% for Xe and Sr). Half-life values of 20 nuclides produced in the decay of krypton and xenon isotopes were measured as well. Like the other noble gases, krypton is chemically unreactive. However, following the first successful synthesis of xenon compounds in 1962, synthesis of krypton difluoride ( KrF2 ) was reported in 1963. In the same year, KrF4 was reported by Grosse, //et al.// but was subsequently shown to be a mistaken identification. There are also unverified reports of a barium salt of a krypton oxoacid. ArKr+ and KrH+ polyatomic ions have been investigated and there is evidence for KrXe or KrXe

Isotopes
Naturally occurring krypton is made of six stable isotopes. In addition, about thirty unstable isotopes and isomers are known. 81Kr, the product of atmospheric reactions, is produced with the other naturally occurring isotopes of krypton. Being radioactive, it has a half-life of 230,000 years. Krypton is highly volatile when it is near surface waters but 81Kr has been used for dating old (50,000–800,000 years) groundwater. 85 Kr is an inert radioactive noble gas with a half-life of 10.76 years. It is produced by the fission of uranium and plutonium, such as in nuclear bomb testing and nuclear reactors.85Kr is released during the reprocessing of fuel rods from nuclear reactors. Concentrations at the North Pole are 30% higher than at the South Pole due to convective mixing.

Natural occurrence
The Earth has retained all of the noble gases that were present at its formation except forhelium. Krypton's concentration in the atmosphere is about 1 ppm. It can be extracted from liquid air by fractional distillation. The amount of krypton in space is uncertain, as the amount is derived from the meteoric activity and that from solar winds. The first measurements suggest an overabundance of krypton in space.