Editing Neon (section)

==Isotopes==
{{Main|Isotopes of neon}}
[[File:Discovery of neon isotopes.JPG|thumb|left|The first evidence for isotopes of a stable element was provided in 1913 by experiments on neon plasma. In the bottom right corner of [[J. J. Thomson]]'s photographic plate are the separate impact marks for the two isotopes neon-20 and neon-22.]]
Neon has three [[stable isotope]]s: <sup>20</sup>Ne (90.48%), <sup>21</sup>Ne (0.27%) and <sup>22</sup>Ne (9.25%).{{NUBASE2020|ref}} <sup>21</sup>Ne and <sup>22</sup>Ne are partly [[primordial isotope|primordial]] and partly [[nucleogenic]] (i.e. made by nuclear reactions of other nuclides with neutrons or other particles in the environment) and their variations in [[natural abundance]] are well understood. In contrast, <sup>20</sup>Ne (the chief [[primordial isotope]] made in stellar [[nucleosynthesis]]) is not known to be nucleogenic or [[radiogenic]], except from the decay of [[oxygen-20]], which is produced in very rare cases of [[cluster decay]] by [[thorium-228]]. The causes of the variation of <sup>20</sup>Ne in the Earth have thus been hotly debated.<ref>{{cite book|isbn = 978-0-521-82316-6|chapter = Neon|page = 303|title = Radiogenic isotope geology|author1 = Dickin, Alan P|date = 2005| publisher=Cambridge University Press }}</ref><ref name="wwwrcanml"/>

The principal [[nuclear reaction]]s generating nucleogenic neon [[isotope]]s start from <sup>24</sup>Mg and <sup>25</sup>Mg, which produce <sup>21</sup>Ne and <sup>22</sup>Ne respectively, after [[neutron capture]] and immediate emission of an [[alpha particle]]. The [[neutron]]s that produce the reactions are mostly produced by secondary spallation reactions from alpha particles, in turn derived from [[uranium]]-series [[decay chain]]s. The net result yields a trend towards lower <sup>20</sup>Ne/<sup>22</sup>Ne and higher <sup>21</sup>Ne/<sup>22</sup>Ne ratios observed in uranium-rich rocks such as [[granite]]s.<ref name="wwwrcanml">[http://wwwrcamnl.wr.usgs.gov/isoig/period/ne_iig.html Resources on Isotopes Periodic Table—Neon] at the [[U.S. Geological Survey]], by Eric Caldwell, posted January 2004, retrieved 10 February 2011</ref>

In addition, isotopic analysis of exposed terrestrial rocks has demonstrated the [[cosmogenic]] (cosmic ray) production of <sup>21</sup>Ne. This isotope is generated by [[spallation]] reactions on [[magnesium]], [[sodium]], [[silicon]], and [[aluminium]]. By analyzing all three isotopes, the cosmogenic component can be resolved from [[magma]]tic neon and nucleogenic neon. This suggests that neon will be a useful tool in determining cosmic exposure ages of surface rocks and [[meteorite]]s.<ref>{{cite web |url=http://nautilus.fis.uc.pt/st2.5/scenes-e/elem/e01093.html |title=Neon: Isotopes |access-date=27 February 2007 |publisher=Softciências |url-status=dead |archive-url=https://web.archive.org/web/20121115190653/http://nautilus.fis.uc.pt/st2.5/scenes-e/elem/e01093.html |archive-date=15 November 2012 }}</ref>

Neon in [[solar wind]] contains a higher proportion of <sup>20</sup>Ne than nucleogenic and cosmogenic sources.<ref name="wwwrcanml"/> Neon content observed in samples of [[volcano|volcanic]] [[gas]]es and [[diamond]]s is also enriched in <sup>20</sup>Ne, suggesting a primordial, possibly solar origin.<ref>{{cite web |url=http://www.mantleplumes.org/Ne.html |title=Helium, Neon & Argon |access-date=2 July 2006 |author=Anderson, Don L. |publisher=Mantleplumes.org |url-status=live |archive-url=https://web.archive.org/web/20060528113659/http://www.mantleplumes.org/Ne.html |archive-date=28 May 2006 }}</ref>