Governing force and Neutron elastic scattering

[oksuz_]

Hi,

Which force does govern the neutron elastic scattering and capture reactions? It seems to me it is the strong nuclear force, but I am not sure about that.Thanks.

 

[mfb]

Sure. No electric charge involved, and the weak interaction is negligible if the strong interaction plays a role.

 

[oksuz_]

Thanks mfb,

Do you have any resources in mind that you can suggest to me about the theory behind these interactions? I want to get some theoretical understanding of calculating these reactions' interaction cross-sections.

 

[mathman]

Elastic scattering is an ordinary collision. Inelastic scattering and capture involve the strong force,

 

[oksuz_]

Elastic scattering is an ordinary collision.

In the macroscopic world, ordinary elastic scattering is governed by the electromagnetic force. Since neutron is an uncharged particle, it cannot be the electromagnetic force. It cannot the gravitational force either. It should be either the strong or weak nuclear force. So, which one?

 

[mfb]

Elastic scattering is an ordinary collision.

Yes, mediated by the strong interaction.

 

[Vanadium 50]

Since neutron is an uncharged particle, it cannot be the electromagnetic force.

It's not primarily the EM force, yes, but that argument is not valid. The neutron has a magnetic moment and can interact electromagnetically that way.

 

[oksuz_]

It's not primarily the EM force, yes, but that argument is not valid. The neutron has a magnetic moment and can interact electromagnetically that way.

Thanks! I missed that part.

Can you tell quantitatively what is the fraction of the interaction level that comes from the EM force compared to the strong force?

 

[mathman]

When two billiard balls collide, none of the four forces are at work. Neutron elastic scattering is basically the same process.

 

[snorkack]

Do billiard balls collide by electromagnetic force or by exchange force?
Neutrons can undergo elastic scattering by strong force (off hadrons).
There are particles not subject to strong force (and not identical to neutrons, so no exchange force either).
Photons are subject to neither strong nor weak forces. But they have electromagnetic forces. Neutron has no electric monopole charge. But does have a nonzero magnetic dipole moment. Therefore photons should have a nonzero but modest cross-section of elastic scattering from neutrons.
Gravitons are subject to gravitational forces alone, but neutrons have mass, therefore elastic scattering of gravitons off neutrons must have a nonzero but modest cross-section.
Neutrinos are subject to neither strong nor electromagnetic forces, but do have weak forces. Therefore elastic scattering of neutrinos off neutrons must have a nonzero but modest cross-section.
Electrons are not subject to strong forces but have both electromagnetic and weak forces. Therefore both electromagnetic interaction between electron charge and neutron magnetic dipole moment and weak interaction must contribute to cross-section of elastic scattering between neutrons and electrons.

 

[mathman]

Exchange force is a microscopic idea, not applying to macroscopic collisions. Billiard balls are neutral so e-m does not apply

 

[snorkack]

Atoms are microscopic and neutral. What force causes two neutral hydrogen atoms to collide? Assume they are different isotopes so no exchange forces between nuclei or atoms - only electrons are identical. The outcome depends on whether the electrons´ spins are same or different - so it must be exchange force, not just electromagnetic.