Xenon ( in the UK, in the US) is a chemical element that has the symbol Xe and atomic number 54. A colorless, heavy, odorless noble gas, xenon occurs in the earth's atmosphere in trace amounts."[LINK: http://www.infoplease.com/ce6/sci/A0852881.html] xenon", Columbia Electronic Encyclopedia, 6th ed., Columbia University Press, 2007. Accessed on line October 23, 2007. Although generally unreactive, xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate, the first noble gas compound to be synthesized.—National Standard Reference Data Service of the USSR. Volume 10. Naturally occurring xenon is made of nine stable isotopes, but there are also over 40 unstable isotopes that undergo radioactive decay. The isotope ratios of xenon are an important tool for studying the early history of the Solar Sys