Talk:Criticality (nuclear)

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 Definition In a nuclear fission chain reaction, the mean number of neutrons produced by a nuclear fission (by one neutron) which cause another fission: (probability to crack a nucleus)*(mean number of neutrons produced by a single fission) [d] [e]
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Spontaneous decay and the neutron scatterers

1. How about to add some refs? for ex.,

2. I think, the role of the neutron scatterers should be discussed.
How about to surround the core with some boron, or, contrary, with some beryllium?
Can it be used to control the fission instead of the conventional control rods?

3. How about to trace the role of the spontaneous decay? for example, if the criticality is slightly below unity, but the stimulated reactions converts each spontaneous neutron to, say, a million of neutrons that get out. In such a condition, the core should show huge fluctuation in generation of energy. There is analogy in optics, it is called "amplified spontaneous emission".

Dmitrii Kouznetsov 15:42, 25 November 2012 (UTC)

I'm not finished writing this article. Perhaps I should have started this on User subpage of mine then moved to a main article page. I plan to rewrite the "section" I just removed. I could write it in terms of reactivity, symbolized by δ or ρ, or in terms of effective neutron multiplication factor, symbolized by Keff. They are related quantities. I'll think about this when I have some time. Henry A. Padleckas 17:56, 26 November 2012 (UTC)
Yes, I understand that you did not finish; for this reason, I do not interfere in the article, I but just formulate the suggestion about the content. As for the reactivity and the multiplication factor, I think, each of these terms should be carefully defined, specified and discussed. Take your time. Dmitrii Kouznetsov 10:47, 27 November 2012 (UTC)

Reactivity and keff

Criticality in a given situation is specified by either one of two quantities, both of which are mathematically related such that physically one is specifying the same condition by using either of the two quantities. The two quantities are reactivity, often symbolized by ρ, and effective neutron multiplication factor, symbolized by k or keff. They are mathematically related as follows:

ρ = (keff - 1) / keff

After pondering the matter for a while, I think I will have the Criticality (nuclear) article cover both of these quantities, instead of writing separate articles for each. Eventually (if that will ever happen) when this article is greatly expanded, the information on these two quantities can be moved to their own separate articles, Reactivity (nuclear) and Effective neutron multiplication factor for which a Definition page has been created - Effective neutron multiplication factor/Definition. Henry A. Padleckas 03:37, 27 November 2012 (UTC)

There should be article Reactivity (nuclear), and the Effective neutron multiplication factor should be mentioned there as related topic, perhaps, as a section or a subsection. But also, there should be article Effective neutron multiplication factor, and the Reactivity (nuclear), should be mentioned there as related topic, perhaps, as a section or a subsection. And the same about Criticality (nuclear). Then one can quickly find the information one need, without to drill all the theory of the chain reaction. Dmitrii Kouznetsov 10:56, 27 November 2012 (UTC)
Conditions for criticality
Criticality condition in terms of
effective neutron
multiplication factor

keff or k
in terms of

ρ (or δ)
subcritical keff < 1.0 ρ < 0.0
critical keff = 1.0 ρ = 0.0
supercritical keff > 1.0 ρ > 0.0
.....delayed supercritical 1.0 < keff < xxxx 0.0 < ρ < xxx
.....prompt supercritical keff < xxxx ρ < xxx