View source for Neon-burning process

{{Short description|Set of nuclear fusion reactions}}
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The '''neon-burning process''' is a set of [[nuclear fusion]] reactions that take place in [[stellar evolution|evolved]] massive [[star]]s with at least 8 [[Solar mass]]es. Neon burning requires high temperatures and [[density|densities]] (around 1.2 billion [[kelvin|K]] or 100 [[keV]] and 4 billion kg/m<sup>3</sup>).

At such high temperatures [[photodisintegration]] becomes a significant effect, so some neon [[atomic nucleus|nuclei]] decompose, absorbing 4.73&nbsp;MeV and releasing [[alpha particle]]s.<ref name="Clayton">{{cite book | last=Clayton | first=Donald | url=http://adsabs.harvard.edu/abs/1983psen.book.....C | title=Principles of Stellar Evolution and Nucleosynthesis | year=1983 | bibcode=1983psen.book.....C }}</ref> This free helium nucleus can then fuse with neon to produce magnesium, releasing 9.316&nbsp;MeV.<ref name=LeBlanc_2011>{{cite book
 | title=An Introduction to Stellar Astrophysics
 | first=Francis | last=LeBlanc | year=2011
 | page=256 | isbn=9781119964971 | publisher=Wiley
 | url=https://books.google.com/books?id=jAe4P3GIZRoC&pg=PT256 }}</ref>

<!-- Autogenerated using Phykiformulae 0.10 by [[User:SkyLined]]
	Ne-20 + y  -> O-16  + He - 4.73 MeV
	Ne-20 + He -> Mg-24 + y + 9.32 MeV
-->:{| border="0"
|- style="height:2em;"
|[[Neon-20|{{nuclide|neon|20}}]]&nbsp;||+&nbsp;||[[Gamma ray|γ]]&nbsp;||→&nbsp;||[[Oxygen-16|{{nuclide|oxygen|16}}]]&nbsp;||+&nbsp;||[[Helium|{{nuclide|helium|4}}]]
|- style="height:2em;"
|[[Neon-20|{{nuclide|neon|20}}]]&nbsp;||+&nbsp;||[[Helium|{{nuclide|helium|4}}]]&nbsp;||→&nbsp;||[[Magnesium-24|{{nuclide|magnesium|24}}]]&nbsp;||+&nbsp;||[[Gamma ray|γ]]
|}

Alternatively:
<!-- Autogenerated using Phykiformulae 0.10 by [[User:SkyLined]]
        Ne-20 + n  -> Ne-21 + y
	Ne-21 + He -> Mg-24 + n
-->:{| border="0"
|- style="height:2em;"
|[[Neon-20|{{nuclide|neon|20}}]]&nbsp;||+&nbsp;||[[Neutron|n]]&nbsp;||→&nbsp;||[[Neon-21|{{nuclide|neon|21}}]]&nbsp;||+&nbsp;||[[Gamma ray|γ]]
|- style="height:2em;"
|[[Neon-21|{{nuclide|neon|21}}]]&nbsp;||+&nbsp;||[[Helium|{{nuclide|helium|4}}]]&nbsp;||→&nbsp;||[[Magnesium-24|{{nuclide|magnesium|24}}]]&nbsp;||+&nbsp;||[[Neutron|n]]
|}

where the neutron consumed in the first step is regenerated in the second.

A secondary reaction causes helium to fuse with magnesium to produce silicon:<ref name=LeBlanc_2011/>

: {{nuclide|Magnesium|24}} + {{nuclide|helium|4}} → [[Silicon|{{nuclide|Silicon|28}}]] + γ

Contraction of the core leads to an increase of temperature, allowing neon to fuse directly as follows:<ref name=LeBlanc_2011/>

: {{nuclide|neon|20}} + {{nuclide|neon|20}} → {{nuclide|oxygen|16}} + {{nuclide|Magnesium|24}}

Neon burning takes place after [[carbon-burning process|carbon burning]] has consumed all [[carbon]] in the core and built up a new [[oxygen]]–[[neon]]–[[sodium]]–[[magnesium]] core. The core ceases producing fusion energy and contracts. This contraction increases density and temperature up to the ignition point of neon burning. The increased temperature around the core allows carbon to burn in a shell, and there will be shells burning helium and [[hydrogen]] outside.

During neon burning, oxygen and magnesium accumulate in the central core while neon is consumed. After a few years the star consumes all its neon and the core ceases producing fusion energy and contracts. Again, gravitational pressure takes over and compresses the central core, increasing its density and temperature until the [[oxygen-burning process]] can start.

==References==
{{Reflist}}

==External links==
* Arnett, W. D. [http://adsabs.harvard.edu/full/1974ApJ...193..169A Advanced evolution of massive stars. V – Neon burning] / Astrophysical Journal, vol. 193, Oct. 1, 1974, pt. 1, p.&nbsp;169–176.

{{Nuclear processes}}

[[Category:Nucleosynthesis]]


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