Editing Prompt neutron (section)

{{Short description|Immediate emission of neutrons after nuclear fission}}
[[File:Gabab4ff2 hr.jpg|thumb|Diagram of a fission event; the prompt neutrons are emitted in the yellow area, after between 10<sup>–18</sup> and 10<sup>–14</sup> seconds.]]
In [[nuclear engineering]], a '''prompt neutron''' is a [[neutron]] immediately emitted ([[neutron emission]]) by a [[nuclear fission]] event, as opposed to a [[delayed neutron|delayed neutron decay]] which can occur within the same context, emitted after [[beta decay]] of one of the [[fission product]]s anytime from a few milliseconds to a few minutes later.

Prompt neutrons emerge from the fission of an unstable [[fissionable]] or [[fissile]] heavy nucleus almost instantaneously. There are different definitions for how long it takes for a prompt neutron to emerge. For example, the [[United States Department of Energy]] defines a prompt neutron as a neutron born from fission within 10<sup>−13</sup> seconds after the fission event.<ref>{{Citation|contribution=DOE Fundamentals Handbook - Nuclear Physics and Reactor Theory|title=DOE Fundamentals Handbook - Nuclear Physics and Reactor Theory|contribution-url=https://www.navsea.navy.mil/Portals/103/Documents/NNPTC/Physics/doe_phys_nuc.pdf|page=29 (p. 133 of .pdf format)|series=DOE-HDBK-1019/1-93|date=January 1993 |publisher=[[U.S. Department of Energy]]}}</ref> The U.S. [[Nuclear Regulatory Commission]] defines a prompt neutron as a neutron emerging from fission within 10<sup>−14</sup> seconds.<ref>{{Citation|first=John T.|last=Mihalczo |title=Radiation Detection From Fission|contribution=Radiation Detection From Fission|contribution-url=http://www.ornl.gov/~webworks/cppr/y2004/rpt/121589.pdf?origin=publication_detail|page=1 (p. 11 of .pdf format)|series=ORNL/TM-2004/234|date=November 19, 2004|publisher=[[Oak Ridge National Laboratory]]}}</ref>
This emission is controlled by the [[nuclear force]] and is extremely fast. By contrast, so-called delayed neutrons are delayed by the time delay associated with beta decay (mediated by the [[Weak interaction|weak force]]) to the precursor excited nuclide, after which neutron emission happens on a prompt time scale (i.e., almost immediately).