Editing Actinide (section)

== Formation in nuclear reactors ==
[[File:Actinide Buildup Chart 03a.png|thumb|upright=1.5|Table of nuclides: Buildup of actinides in a nuclear reactor, including radioactive decay]]
The figure ''buildup of actinides'' is a table of nuclides with the number of neutrons on the horizontal axis (isotopes) and the number of protons on the vertical axis (elements). The red dot divides the nuclides in two groups, so the figure is more compact. Each nuclide is represented by a square with the mass number of the element and its half-life.<ref>{{cite journal | last1=Soppera | first1=N. | last2=Bossant | first2=M. | last3=Dupont | first3=E. | title=JANIS 4: An Improved Version of the NEA Java-based Nuclear Data Information System | journal=Nuclear Data Sheets | publisher=Elsevier BV | volume=120 | year=2014 | doi=10.1016/j.nds.2014.07.071 | pages=294–296| bibcode=2014NDS...120..294S }}</ref> Naturally existing actinide isotopes (Th, U) are marked with a bold border, alpha emitters have a yellow colour, and beta emitters have a blue colour. Pink indicates electron capture (<sup>236</sup>Np), whereas white stands for a long-lasting [[nuclear isomer|metastable state]] (<sup>242</sup>Am).

The formation of actinide nuclides is primarily characterised by:<ref>Matthew W. Francis et al. (2014). [https://info.ornl.gov/sites/publications/Files/Pub52057.pdf Reactor fuel isotopics and code validation for nuclear applications]. ORNL/TM-2014/464, Oak Ridge, Tennessee, p. 11</ref>
* [[Neutron capture]] reactions (n,γ), which are represented in the figure by a short right arrow.
* The (n,2n) reactions and the less frequently occurring (γ,n) reactions are also taken into account, both of which are marked by a short left arrow.
* Even more rarely and only triggered by fast neutrons, the (n,3n) reaction occurs, which is represented in the figure with one example, marked by a long left arrow.

In addition to these neutron- or gamma-induced [[nuclear reaction]]s, the radioactive conversion of actinide nuclides also affects the nuclide inventory in a reactor. These decay types are marked in the figure by diagonal arrows. The [[beta decay|beta-minus decay]], marked with an arrow pointing up-left, plays a major role for the balance of the particle densities of the nuclides. Nuclides decaying by [[positron emission]] (beta-plus decay) or [[electron capture]] (ϵ) do not occur in a nuclear reactor except as products of knockout reactions; their decays are marked with arrows pointing down-right. Due to the long half-lives of the given nuclides, [[alpha decay]] plays almost no role in the formation and decay of the actinides in a power reactor, as the residence time of the nuclear fuel in the reactor core is rather short (a few years). Exceptions are the two relatively short-lived nuclides <sup>242</sup>Cm (T<sub>1/2</sub>&nbsp;= 163&nbsp;d) and <sup>236</sup>Pu (T<sub>1/2</sub>&nbsp;= 2.9&nbsp;y). Only for these two cases, the α decay is marked on the nuclide map by a long arrow pointing down-left. A few long-lived actinide isotopes, such as <sup>244</sup>Pu and <sup>250</sup>Cm, cannot be produced in reactors because neutron capture does not happen quickly enough to bypass the short-lived beta-decaying nuclides <sup>243</sup>Pu and <sup>249</sup>Cm; they can however be generated in nuclear explosions, which have much higher neutron fluxes.