Editing Nuclear fusion (section)

== Process ==
[[File:Deuterium-tritium fusion.svg|thumb|Fusion of [[deuterium]] with [[tritium]] creating [[helium-4]], freeing a neutron, and releasing 17.59 [[Electronvolt|MeV]] as [[kinetic energy]] of the products while a corresponding amount of [[Mass–energy equivalence|mass disappears]], in agreement with ''kinetic E'' = ∆''mc''<sup>2</sup>, where Δ''m'' is the decrease in the total rest mass of particles<ref name=Shultis>
{{cite book
 |author1=Shultis, J.K.  |author2=Faw, R.E. 
 |name-list-style=amp |year=2002
 |title=Fundamentals of nuclear science and engineering
 |url=https://books.google.com/books?id=SO4Lmw8XoEMC&pg=PA151
 |page=151
 |publisher=[[CRC Press]]
 |isbn=978-0-8247-0834-4
}}</ref>]]
The release of energy with the fusion of light elements is due to the interplay of two opposing forces: the [[nuclear force]], a manifestation of the [[strong interaction]], which holds protons and neutrons tightly together in the [[atomic nucleus]]; and the [[Coulomb's law|Coulomb force]], which causes positively [[Electric charge|charged]] [[proton]]s in the nucleus to repel each other.<ref>[http://www.ck12.org/flexbook/chapter/1903 Physics Flexbook] {{webarchive|url=https://web.archive.org/web/20111228011150/http://www.ck12.org/flexbook/chapter/1903 |date=28 December 2011 }}. Ck12.org. Retrieved 19 December 2012.</ref> Lighter nuclei (nuclei smaller than iron and nickel) are sufficiently small and proton-poor to allow the nuclear force to overcome the Coulomb force. This is because the nucleus is sufficiently small that all nucleons feel the short-range attractive force at least as strongly as they feel the infinite-range Coulomb repulsion. Building up nuclei from lighter nuclei by fusion releases the extra energy from the net attraction of particles. [[iron peak|For larger nuclei]], however, no energy is released, because the nuclear force is short-range and cannot act across larger nuclei.

Fusion powers [[star]]s and produces most elements lighter than cobalt in a process called [[nucleosynthesis]]. The Sun is a main-sequence star, and, as such, generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core, the Sun fuses 620&nbsp;million metric tons of hydrogen and makes 616&nbsp;million metric tons of helium each second.<!-- Meant generally; please do not insert info about [[stellar nucleosynthesis]], [[supernova nucleosynthesis]] and other types of specific nucleosynthesis here. --> The fusion of lighter elements in stars releases energy and the mass that always accompanies it. For example, in the fusion of two hydrogen nuclei to form helium, 0.645% of the mass is carried away in the form of kinetic energy of an [[alpha particle]] or other forms of energy, such as electromagnetic radiation.<ref name="bulletin1950">{{cite journal |last=Bethe |first=Hans A. |url=https://books.google.com/books?id=Mg4AAAAAMBAJ&pg=PA99 |title=The Hydrogen Bomb |journal=Bulletin of the Atomic Scientists |date=April 1950 |volume=6 |issue=4 |pages=99–104, 125– |doi=10.1080/00963402.1950.11461231 |bibcode=1950BuAtS...6d..99B |access-date=14 September 2018 |archive-date=14 January 2023 |archive-url=https://web.archive.org/web/20230114063514/https://books.google.com/books?id=Mg4AAAAAMBAJ&pg=PA99 |url-status=live |url-access=subscription }}</ref>

It takes considerable energy to force nuclei to fuse, even those of the lightest element, [[hydrogen]]. When accelerated to high enough speeds, nuclei can overcome this electrostatic repulsion and be brought close enough such that the attractive [[nuclear force]] is greater than the repulsive Coulomb force. The [[strong force]] grows rapidly once the nuclei are close enough, and the fusing nucleons can essentially "fall" into each other and the result is fusion; this is an [[exothermic reaction|exothermic process]].<ref>{{cite book |last1=Smith |first1=Peter F. |title=Building for a Changing Climate: The Challenge for Construction, Planning and Energy |date=2009 |publisher=Earthscan |isbn=978-1-84977-439-0 |page=129 |url=https://books.google.com/books?id=Dx-ZkpLS4wMC |language=en |access-date=20 June 2023 |archive-date=5 November 2023 |archive-url=https://web.archive.org/web/20231105221740/https://books.google.com/books?id=Dx-ZkpLS4wMC |url-status=live }}</ref>

Energy released in most [[nuclear reaction]]s is much larger than in [[chemical reaction]]s, because the [[binding energy]] that holds a nucleus together is greater than the energy that holds [[electron]]s to a nucleus. For example, the [[ionization energy]] gained by adding an electron to a hydrogen nucleus is {{val|13.6|ul=eV}}—less than one-millionth of the {{val|17.6|ul=MeV}} released in the [[deuterium]]–[[tritium]] (D–T) reaction shown in the adjacent diagram. Fusion reactions have an [[energy density]] many times greater than [[nuclear fission]]; the reactions produce far greater energy per unit of mass even though ''individual'' fission reactions are generally much more energetic than ''individual'' fusion ones, which are themselves millions of times more energetic than chemical reactions. Via the [[mass–energy equivalence]], fusion yields a 0.7% efficiency of reactant mass into energy. This can be only be exceeded by the extreme cases of the [[Accretion disk|accretion]] process involving neutron stars or black holes, approaching 40% efficiency, and [[antimatter]] [[annihilation]] at 100% efficiency. (The complete conversion of one gram of matter would expel {{val|9|e=13|u=joules}} of energy.)