Understanding Neutron Diffusion in Nuclear Reactions

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Discussion Overview

The discussion revolves around the concept of neutron diffusion in nuclear reactions, particularly focusing on the behavior of neutrons in a medium, their interactions, and the distinction between diffusion and nuclear reactions. Participants explore theoretical aspects, definitions, and implications of neutron diffusion, including conditions under which it occurs.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants question whether neutron diffusion refers to neutrons traveling outside the nucleus or if it involves neutrons bouncing off nuclei without reactions.
  • It is noted that neutrons can scatter or react with nuclei, and in thick media, their transport can be modeled as diffusion.
  • There is a discussion about the meaning of neutron diffusion when no nuclear reactions occur, with some suggesting it implies only elastic scattering.
  • One participant describes neutron diffusion as a movement from areas of high neutron density to low density, influenced by scattering collisions, under certain conditions like isotropic scattering and constant flux.
  • Another participant provides an analogy comparing neutron diffusion to moving balls spreading out in a space, highlighting the simplifications involved in this analogy.
  • Some participants clarify that diffusion can still occur due to scattering even when absorption and generation terms are zero, referencing Flick's law.
  • There is a request for clarification on the distinction between scattering and nuclear reactions, with some asserting that scattering does not count as a nuclear reaction.
  • Concerns are raised about how nuclear diffusion can change the number of nucleons in a nucleus without being classified as a nuclear reaction.
  • Participants discuss the nature of free neutrons in relation to neutron diffusion, emphasizing that these are not the neutrons within the nucleus.
  • There is uncertainty about whether nuclear reactions can occur with just one neutron.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and implications of neutron diffusion and its relationship to nuclear reactions. There is no consensus on the interpretations of neutron diffusion, scattering, and their respective roles in nuclear processes.

Contextual Notes

Limitations include potential misunderstandings of terminology, the dependence on specific definitions of nuclear reactions, and the conditions under which neutron diffusion is applicable. Some mathematical steps and assumptions remain unresolved.

Who May Find This Useful

This discussion may be of interest to students and professionals in nuclear physics, engineering, and related fields who are exploring the concepts of neutron behavior in materials and the theoretical frameworks surrounding nuclear reactions.

Physicsissuef
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Is neutron diffusion, traveling neutrons from the nucleus, to direction outside of the nucleus? In my textbook says that there is neutron diffusion, where there is not nuclear reaction. In that case are neutron bouncing off the nucleus?
 
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Neutrons moving through a medium can either react with it or scatter. In all cases the interactions are with nuclei. The electrons are too small to have any effect.

When neutrons are going through thick media, i.e. lots of scattering, the transport can be modeled as diffusion.
 
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In this case, it says that it doesn't react with the nucleus, but there is neutron diffusion. What that means?
 
heeelp please! urgent! :D
 
In this case, it says that it doesn't react with the nucleus, but there is neutron diffusion. What that means?
I presume the text means that nothing happens except elastic scattering with the nuclei. There is no nuclear reaction, such as absorption or inelelastic scattering.

When there is no reaction at all, the neutron travels in a straight line, so diffusion will not be a good approximation.
 
Netronic diffusion explain how neutron will move inside a material, neutrons will move due to a difference of density of neutron from higher density neutron zone to a lower neutron density zone, due to that in a high density neutron zone there will be more scattering collision than in a lower density zone , so there will be a neutron current.
This under certian condition like , isotropic scattering, no neutron source inside the material and costant flux.
Well at least this is what I remember...may be there is something wrong.
 
So there will be just, elastic collision? But can anybody explain what is neutron diffusion with simpler words??
 
Well it's the "law" that explain the neutron flux.
It's like ..humm...a space with a high number of moving balls, those will spread around the space to zone where there are less balls, you can see that the moving balls will spread around in zone where there are less balls, this because you will have less collision between balls ( elastic scattering) in that zone.
This is a semplification of diffusion, because in this case it doesn't keeps in count absorbion, material proprietiesù and generation of new neutron inside the material and
 
Physicsissuef said:
heeelp please! urgent! :D

is this a course work question??
 
  • #10
PhilippH said:
Well it's the "law" that explain the neutron flux.
It's like ..humm...a space with a high number of moving balls, those will spread around the space to zone where there are less balls, you can see that the moving balls will spread around in zone where there are less balls, this because you will have less collision between balls ( elastic scattering) in that zone.
This is a semplification of diffusion, because in this case it doesn't keeps in count absorbion, material proprietiesù and generation of new neutron inside the material and

But why in my textbook says that there isn't any nuclear reaction, but there is nuclear diffusion?

malawi_glenn said:
is this a course work question??

No it is not. I was just bumping the thread...
 
  • #11
Because diffusion is composed by a sum of different terms, and if your temrs ( assorbtion and generation) that describe the nuclear reaction are 0, there still a term that describe the neutron collision and this term involves the "Flick law" so there still neutron diffusion also without nuclear reacion.
 
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  • #12
scattering does not count as a nuclear reaction (at least not in general).

Can u please cite the book?
 
  • #13
malawi_glenn said:
scattering does not count as a nuclear reaction (at least not in general).

Can u please cite the book?

No, it doesn't count as nuclear reaction.
My english is not very good so may be wasn't much clear.
I ment that if asobtion and generation ( S) are nill, there still diffusion due to scattering.

The text is: "B. Montagnini - Lezioni di Fisica del Reattore Nucleare - Università di Pisa, 1983"
 
  • #14
How is that nuclear diffusion is not nuclear reaction, but it changes the number of nucleons in the nucleus?
 
  • #15
The neutrons that are taken in consideration aren't the neutron of nucleus, but "free" neutrons coming from some source.
 
  • #16
But does the nuclear reaction is made just using one neutron?
 

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