Editing Nuclear reaction (section)

==Notable types==
While the number of possible nuclear reactions is immense, there are several types that are more common, or otherwise notable. Some examples include:
*[[Nuclear fusion|Fusion]] reactions – two light nuclei join to form a heavier one, with additional particles (usually protons or neutrons) emitted subsequently.
*[[Spallation#Nuclear spallation|Spallation]] – a nucleus is hit by a particle with sufficient energy and momentum to knock out several small fragments or smash it into many fragments.
*[[Induced gamma emission]] belongs to a class in which only photons were involved in creating and destroying states of nuclear excitation.
*[[Nuclear fission|Fission]] reactions – a very heavy nucleus, after absorbing additional light particles (usually neutrons), splits into two or sometimes three pieces. This is an induced nuclear reaction. [[Spontaneous fission]], which occurs without assistance of a neutron, is usually not considered a nuclear reaction. At most, it is not an ''induced'' nuclear reaction.

===Direct reactions===
An intermediate energy projectile transfers energy or picks up or loses nucleons to the nucleus in a single quick (10<sup>−21</sup> second) event. Energy and momentum transfer are relatively small. These are particularly useful in experimental nuclear physics, because the reaction mechanisms are often simple enough to calculate with sufficient accuracy to probe the structure of the target nucleus.

====Inelastic scattering====
{{Main|Inelastic scattering}}

Only energy and momentum are transferred.
*(p,p') tests differences between nuclear states.
*(α,α') measures nuclear surface shapes and sizes. Since α particles that hit the nucleus react more violently, [[elastic scattering|elastic]] and shallow inelastic α scattering are sensitive to the shapes and sizes of the targets, like [[light scattering|light scattered]] from a small black object.
*(e,e') is useful for probing the interior structure. Since electrons interact less strongly than do protons and neutrons, they reach to the centers of the targets and their [[wave function]]s are less distorted by passing through the nucleus.

==== Charge-exchange reactions ====
Energy and charge are transferred between projectile and target. Some examples of this kind of reactions are:

* (p,n)
* (<sup>3</sup>He,t)

====<span class="anchor" id="Transfer reactions"></span>Nucleon transfer reactions====
Usually at moderately low energy, one or more nucleons are transferred between the projectile and target. These are useful in studying outer [[nuclear shell model|shell]] structure of nuclei. Transfer reactions can occur:
* from the projectile to the target - [[Stripping reaction (physics)|stripping reactions]]
* from the target to the projectile - pick-up reactions
Examples:
*(α,n) and (α,p) reactions. Some of the earliest nuclear reactions studied involved an alpha particle produced by [[alpha decay]], knocking a nucleon from a target nucleus.
*(d,n) and (d,p) reactions. A [[deuteron]] [[ion beam|beam]] impinges on a target; the target nuclei absorb either the neutron or proton from the deuteron. The deuteron is so loosely bound that this is almost the same as proton or neutron capture. A compound nucleus may be formed, leading to additional neutrons being emitted more slowly. (d,n) reactions are used to generate energetic neutrons.
*The [[strangeness]] exchange reaction ([[Kaon|K]], [[Pion|π]]) has been used to study [[hypernucleus|hypernuclei]].
*The reaction <sup>14</sup>N(α,p)<sup>17</sup>O performed by Rutherford in 1917 (reported 1919), is generally regarded as the first [[nuclear transmutation]] experiment.

====Reactions with neutrons====
{| class="wikitable" style="float:right;"
|-
! !! → [[tritium|T]] !! → [[Lithium-7|<sup>7</sup>Li]] !! → [[carbon-14|<sup>14</sup>C]] !! !!
|-
|'''(n,''α'')'''||[[lithium-6|<sup>6</sup>Li]] + n → T + ''α'' || [[boron-10|<sup>10</sup>B]] + n → <sup>7</sup>Li + ''α'' ||<sup>17</sup>O + n → <sup>14</sup>C + ''α'' || <sup>21</sup>Ne + n → <sup>18</sup>O + α ||<sup>37</sup>Ar + n → <sup>34</sup>S + ''α''
|-
|'''[[np reaction|(n,p)]]'''||[[helium-3|<sup>3</sup>He]] + n → T + p || <sup>7</sup>Be + n → <sup>7</sup>Li + p ||[[nitrogen-14|<sup>14</sup>N]] + n → <sup>14</sup>C + p || <sup>22</sup>Na + n → <sup>22</sup>Ne + p ||
|-
|'''[[Neutron capture|(n,''γ'')]]'''||[[Deuterium|<sup>2</sup>H]] + n → T + ''γ'' ||bgcolor=lightgrey| ||<sup>13</sup>C + n → <sup>14</sup>C + ''γ'' || ||
|}

Reactions with [[neutron]]s are important in [[nuclear reactor]]s and [[nuclear weapon]]s. While the best-known neutron reactions are [[neutron scattering]], [[neutron capture]], and [[nuclear fission]], for some light nuclei (especially [[odd-odd nuclei]]) the most probable reaction with a [[thermal neutron]] is a transfer reaction:

Some reactions are only possible with [[fast neutrons]]:
*(n,2n) reactions produce small amounts of [[protactinium-231]] and [[uranium-232]] in the [[thorium cycle]] which is otherwise relatively free of highly radioactive [[actinide]] products.
*<sup>9</sup>Be + n → 2''α'' + 2n can contribute some additional neutrons in the [[beryllium]] [[neutron reflector]] of a [[nuclear weapon]].
*<sup>7</sup>Li + n → [[tritium|T]] + ''α'' + n unexpectedly contributed additional yield in the [[Castle Bravo|Bravo]], [[Castle Romeo|Romeo]] and [[Castle Yankee|Yankee]] shots of [[Operation Castle]], the three highest-yield [[nuclear test]]s conducted by the U.S.

==={{Anchor|compound nucleus}} Compound nuclear reactions===
<!-- This Anchor tag serves to provide a permanent target for incoming section links. Please do not move it out of the section heading, even though it disrupts edit summary generation (you can manually fix the edit summary before saving your changes). Please do not modify it, even if you modify the section title. It is always best to anchor an old section header that has been changed so that links to it won't be broken. See [[Template:Anchor]] for details. (This text: [[Template:Anchor comment]]) -->Either a low-energy projectile is absorbed or a higher energy particle transfers energy to the nucleus, leaving it with too much energy to be fully bound together. On a time scale of about 10<sup>−19</sup> seconds, particles, usually neutrons, are "boiled" off. That is, it remains together until enough energy happens to be concentrated in one neutron to escape the mutual attraction. The excited quasi-bound nucleus is called a '''compound nucleus'''.
*Low energy (e, e' xn), (γ, xn) (the xn indicating one or more neutrons), where the gamma or virtual gamma energy is near the [[giant dipole resonance]]. These increase the need for [[radiation shielding]] around [[electron accelerator]]s.