Editing Neutron radiation (section)

== Sources ==
{{Main|Neutron source}}
{{See also|Category:Neutron sources}}

[[Neutron]]s may be emitted from [[nuclear fusion]] or [[nuclear fission]], or from other [[nuclear reaction]]s such as [[radioactive decay]] or particle interactions with [[cosmic ray]]s or within [[particle accelerator]]s. Large neutron sources are rare, and usually limited to large-sized devices such as [[nuclear reactor]]s or [[particle accelerator]]s, including the [[Spallation Neutron Source]].

Neutron radiation was discovered from observing  an [[alpha particle]] colliding with a [[beryllium]] [[atomic nucleus|nucleus]], which was transformed into a [[carbon]] [[atomic nucleus|nucleus]] while emitting a [[neutron]], [[Beryllium|Be]]([[alpha particle|α]], [[neutron|n]])[[Carbon|C]]. The combination of an alpha particle emitter and an isotope with a large ([[alpha particle|α]], [[neutron|n]]) [[cross section (physics)|nuclear reaction probability]] is still a common neutron source.

=== Neutron radiation from fission ===
The neutrons in nuclear reactors are generally categorized as [[slow neutron|slow (thermal) neutrons]] or [[fast neutron]]s depending on their energy. Thermal neutrons are similar in energy distribution (the [[Maxwell–Boltzmann distribution]]) to a gas in [[thermodynamic equilibrium]]; but are easily captured by atomic nuclei and are the primary means by which elements undergo [[nuclear transmutation]].

To achieve an effective fission chain reaction, neutrons produced during fission must be captured by fissionable nuclei, which then split, releasing more neutrons. In most fission reactor designs, the [[nuclear fuel]] is not sufficiently refined to absorb enough fast neutrons to carry on the chain reaction, due to the lower [[Cross section (physics)|cross section]] for higher-energy neutrons, so a [[neutron moderator]] must be introduced to slow the fast neutrons down to thermal velocities to permit sufficient absorption. Common neutron moderators include [[graphite]], ordinary (light) [[water]] and [[heavy water]]. A few reactors ([[fast neutron reactor]]s) and all [[nuclear weapon]]s rely on fast neutrons.

=== Cosmogenic neutrons ===
{{uncited section|date=June 2022}}
{{Main|Cosmogenic neutron}}
Cosmogenic neutrons are produced from cosmic radiation in the Earth's atmosphere or surface, as well as in particle accelerators. They often possess higher energy levels compared to neutrons found in reactors. Many of these neutrons activate atomic nuclei before reaching the Earth's surface, while a smaller fraction interact with nuclei in the atmospheric air.<ref>{{Cite web |date=2022-10-26 |title=Cosmogenic Nucleide Principle - CEREGE |url=https://www.cerege.fr/en/equipment/laboratoire-national-des-nucleides-cosmogeniques/principle-of-cosmogenic-nucleides/ |access-date=2024-07-16 |website=www.cerege.fr |language=en-GB}}</ref> When these neutrons interact with nitrogen-14 atoms, they can transform them into [[carbon-14]] (14C), which is extensively utilized in [[radiocarbon dating]].<ref>{{Cite web |title=What is Carbon Dating? {{!}} University of Chicago News |url=https://news.uchicago.edu/explainer/what-is-carbon-14-dating#how |access-date=2024-09-19 |website=news.uchicago.edu |language=en}}</ref>