![]() ![]() Neon is the second-lightest noble gas, glows reddish- orange in a vacuum discharge tube and has over 40 times the refrigerating capacity of liquid helium and three times that of liquid hydrogen (on a per unit volume basis). Elevated 20Ne abundances are found in diamonds, further suggesting a solar neon reservoir in the Earth. The 20Ne-enriched components are attributed to exotic primordial rare gas components in the Earth, possibly representing solar neon. The neon isotopic content of these mantle-derived samples represent a non-atmospheric source of neon. Similar to xenon, neon content observed in samples of volcanic gases are enriched in 20Ne, as well as nucleogenic 21Ne, relative to 22Ne content. This suggests that neon will be a useful tool in determining cosmic exposure ages of surficial rocks and meteorites. By analyzing all three isotopes, the cosmogenic component can be resolved from magmatic neon and nucleogenic neon. This isotope is generated by spallation reactions on magnesium, sodium, silicon, and aluminium. Isotopic analysis of exposed terrestrial rocks has demonstrated the cosmogenic production of 21Ne. The net result yields a trend towards lower 20Ne/ 22Ne and higher 21Ne/ 22Ne ratios observed in uranium-rich rocks such as granites. The alpha particles are derived from uranium-series decay chains, while the neutrons are mostly produced by secondary reactions from alpha particles. The principal nuclear reactions which generate neon isotopes are neutron emission, alpha decay reactions on 24Mg and 25Mg, which produce 21Ne and 22Ne, respectively. In contrast, 20Ne is not known to be nucleogenic and the causes of its variation in the Earth have been hotly debated. 21Ne and 22Ne are nucleogenic and their variations are well understood. ![]()
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