Understanding Neutron Diffusion in Nuclear Reactions

[Physicsissuef]

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?

 

[mathman]

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.

 

[Physicsissuef]

In this case, it says that it doesn't react with the nucleus, but there is neutron diffusion. What that means?

 

[Physicsissuef]

heeelp please! urgent! :D

 

[mathman]

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.

 

[PhilippH]

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.

 

[Physicsissuef]

So there will be just, elastic collision? But can anybody explain what is neutron diffusion with simpler words??

 

[PhilippH]

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 betwen balls ( elastic scattering) in that zone.
This is a semplification of diffusion, because in this case it dosen't keeps in count absorbion, material proprietiesù and generation of new neutron inside the material and

 

[malawi_glenn]

heeelp please! urgent! :D

is this a course work question??

 

[Physicsissuef]

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 betwen balls ( elastic scattering) in that zone.
This is a semplification of diffusion, because in this case it dosen'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?

is this a course work question??

No it is not. I was just bumping the thread...

 

[PhilippH]

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.

 

[malawi_glenn]

scattering does not count as a nuclear reaction (at least not in general).

Can u please cite the book?

 

[PhilippH]

scattering does not count as a nuclear reaction (at least not in general).

Can u please cite the book?

No, it dosen'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"

 

[Physicsissuef]

How is that nuclear diffusion is not nuclear reaction, but it changes the number of nucleons in the nucleus?

 

[PhilippH]

The neutrons that are taken in consideration aren't the neutron of nucleus, but "free" neutrons coming from some source.

 

[Physicsissuef]

But does the nuclear reaction is made just using one neutron?