Do neutrons attract, repel, or have no effect on each other?

all nucleons attract all other nucleons

The nucleus tends toward a certain ratio of protons to neutrons, a ratio which starts at about 1:1 but then increases as mass increases. Far from the ratio, the nucleus tends to decay in such a way as to bring it closer to the ratio. I'm not sure if this really relates to your question, but I think that they both attract and repel each other.

The answer you are looking for really depends on why you are asking.

If this is a conceptual highschool level homework question, then probably you would want to say they have no effect because they are electrically neutral.

 

However, the more detailed answer is that out of the 4 fundamental forces, 2 of them act between neutrons.

They are the gravitational interaction, and the strong interaction.

 

Gravity acts because they have masses, however make sure that you understand this effect is extremely tiny. It is negligible and is almost always considered to not be present.

 

So the only interaction that matters is the strong nuclear interaction. Neutrons and protons are actually composite particles, meaning they are made up of smaller fundamental particles called "quarks".

The strong force acts between these quarks and is the strongest of the 4 interactions, therefore it easily overcomes any electrical repulsion.

The question really is "what is the force between nucleons?"

 

The force between nucleons is called the nuclear force or sometimes the residual strong force. It is some kind of "effective" force due to the strong force. Note that as nucleons are colourless, this force does not directly involve gluon exchange.

 

In principle, one should be able to calculate everything within the framework of an SU(3) Yang-Mills Lagrangian. However, in reality that is too hard at the moment. People use more phenomenological based low energy models including:

 

Nonrelativistic potential models.

The Skyrme model.

MIT bag model.

 

and I am sure many others.

 

From "first principles" the only approach that is possible at the moment is lattice QCD on supercomputers. There is a lot of interest in matching particle physics with nuclear physics.

Edited September 24, 201015 yr by ajb

So cold neutrons would stick into groups? Possibly congeal into at least atomic nucleus sized group particles? Bigger? Small macro objects made of neutronium? What would be the limit? Free neutrons decay, would clusters of neutrons be stable like they are inside a nucleus?

Edited September 24, 201015 yr by Moontanman

So cold neutrons would stick into groups? Possibly congeal into at least atomic nucleus sized group particles? Bigger? Small macro objects made of neutronium? What would be the limit? Free neutrons decay, would clusters of neutrons be stable like they are inside a nucleus?

 

IIRC, two neutrons cannot form a bound state. Even of they could, it would be unstable and decay, either splitting it up or forming Deuterium. Larger collections would likewise be unstable — there would always be unoccupied proton states representing a lower energy state. They might be formed temporarily in a reaction, but would not be a final product.

 

Neutronium can form because of the large gravitational energy involved, but this will only manifest itself when you have a lot of mass.

IIRC, two neutrons cannot form a bound state. Even of they could, it would be unstable and decay, either splitting it up or forming Deuterium. Larger collections would likewise be unstable — there would always be unoccupied proton states representing a lower energy state. They might be formed temporarily in a reaction, but would not be a final product.

 

Neutronium can form because of the large gravitational energy involved, but this will only manifest itself when you have a lot of mass.

 

 

Thanks swansont, exactly what I needed to know...