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In nuclear engineering, a prompt neutron is a neutron immediately emitted (neutron emission) by a nuclear fission event, as opposed to a delayed neutron decay which can occur within the same context, emitted after beta decay of one of the fission products anytime from a few milliseconds to a few minutes later.
In nuclear engineering, a prompt neutron is a neutron immediately emitted by a nuclear fission event. Prompt neutrons emerge from the fission of an unstable fissionable or fissile heavy nucleus almost instantaneously. Delayed neutron decay can occur within the same context, emitted after beta decay of one of the fission products.
A subcritical mass is a mass that does not have the ability to sustain a fission chain reaction. A population of neutrons introduced to a subcritical assembly will exponentially decrease. In this case, known as subcriticality, k < 1. A critical mass is a mass of fissile material that self-sustains a fission chain reaction.
In nuclear engineering, a delayed neutron is a neutron emitted after a nuclear fission event, by one of the fission products (or actually, a fission product daughter after beta decay), any time from a few milliseconds to a few minutes after the fission event. Neutrons born within 10 −14 seconds of the fission are termed "prompt neutrons".
The following list of prompt critical power excursions is adapted from a report submitted in 2000 by a team of American and Russian nuclear scientists who studied criticality accidents, published by the Los Alamos Scientific Laboratory, the location of many of the excursions. [4] A typical power excursion is about 1 x 10 17 fissions.
The mean generation time, λ, is the average time from a neutron emission to a capture that results in fission. [16] The mean generation time is different from the prompt neutron lifetime because the mean generation time only includes neutron absorptions that lead to fission reactions (not other absorption reactions).
The prompt neutron lifetime in a modern thermal reactor is about 10 −4 seconds, thus it is not feasible to control reactor behavior with prompt neutrons alone. Reactor time behavior can be characterized by weighing the prompt and delayed neutron yield fractions to obtain the average neutron lifetime, Λ=l/k, or the mean generation time ...
The neutrons are usually classified in 6 delayed neutron groups. [4] The average neutron lifetime considering delayed neutrons is approximately 0.1 sec, which makes the chain reaction relatively easy to control over time. The remaining 993 prompt neutrons are released very quickly, approximately 1 μs after the fission event.