Editing Delayed neutron (section)

{{Short description|Delayed emission of neutrons after nuclear fission}}
In [[nuclear engineering]], a '''delayed neutron''' is a [[neutron]] released not immediately during a [[nuclear fission]] event, but shortly afterward—ranging from milliseconds to several minutes later. These neutrons are emitted by excited [[Decay product|daughter nuclei]] of certain beta-decaying [[fission product]]s. In contrast, '''[[Prompt neutron|prompt neutrons]]''' are emitted almost instantaneously—within about 10<sup>−14</sup> seconds—at the moment of fission.

During fission, a heavy nucleus splits into two smaller, neutron-rich fragments (fission products), releasing several free neutrons known as prompt neutrons. Many of these fission products are [[Radioactive decay|radioactive]] and typically undergo beta decay to reach more stable configurations. In a small subset of cases, the beta decay of a fission product results in a [[Decay product|daughter nucleus]] in an excited state with enough energy to emit a neutron. This neutron, emitted shortly after fission but delayed due to the beta decay process, is called a delayed neutron.

The delay in neutron emission arises from the time required for the precursor nuclide (the beta-decaying fission product) to undergo beta decay—a process that takes orders of magnitude longer than the prompt emission of neutrons during fission. While the delayed neutron is emitted almost immediately after beta decay, it is actually released by the excited daughter nucleus produced in that decay. Therefore, the overall timing of delayed neutron emission is governed by the beta decay [[half-life]] of the precursor.

Delayed neutrons are critically important for controlling nuclear reactors. Their delayed appearance allows for a [[Nuclear chain reaction#Special reactivity cases|slower, more manageable response]] in reactor power changes, significantly enhancing both operational stability and safety.