Neutrons attractive or repulsive?

[Moontanman]

Do free neutrons attract, repel, or ignore each other?  

[swansont]

1 hour ago, Moontanman said:

Do free neutrons attract, repel, or ignore each other?  

They tend to increase the binding energy per nucleon of nuclei, which one would interpret as an attraction. Also, mirror nuclei (same number of nucleons by neutron and proton number switched) show that all the nucleons attract each other in the same way.

The interaction has a limited range, though.

You can’t form a stable nucleus with just neutrons, or mostly neutrons, though, because it’s energetically favorable for neutrons to decay into protons in those situations.

[Moontanman]

1 minute ago, swansont said:

They tend to increase the binding energy per nucleon of nuclei, which one would interpret as an attraction. Also, mirror nuclei (same number of nucleons by neutron and proton number switched) show that all the nucleons attract each other in the same way.

The interaction has a limited range, though.

You can’t form a stable nucleus with just neutrons, or mostly neutrons, though, because it’s energetically favorable for neutrons to decay into protons in those situations.

I was thinking more of neutrons freely moving around not neutrons bound together, I am thinking of a coherent beam of neutrons or even a cloud of neutrons, do they repel, attract or ignore each other. I am thinking of a weapon for a novel but I'd like to know how neutrons react to each other before I begin to speculate.  

[swansont]

Just now, Moontanman said:

I was thinking more of neutrons freely moving around not neutrons bound together, I am thinking of a coherent beam of neutrons or even a cloud of neutrons, do they repel, attract or ignore each other. I am thinking of a weapon for a novel but I'd like to know how neutrons react to each other before I begin to speculate.  

The fact that neutrons can be bound shows that they attract. You can make a neutron beam, but not sure how you’d get a coherent beam. A coherent beam might be more of a problem, since the neutrons would have basically the same speed, and thus have little KE in the beam’s frame. I suspect you’d form dineutrons which would very quickly decay to deuterium or a free proton snd neutron. Neutrons with different energies wouldn’t get trapped in each other’s potential well so easily.

[Moontanman]

11 minutes ago, swansont said:

The fact that neutrons can be bound shows that they attract. You can make a neutron beam, but not sure how you’d get a coherent beam. A coherent beam might be more of a problem, since the neutrons would have basically the same speed, and thus have little KE in the beam’s frame. I suspect you’d form dineutrons which would very quickly decay to deuterium or a free proton snd neutron. Neutrons with different energies wouldn’t get trapped in each other’s potential well so easily.

Thank you, that gives me room to play! I've figured out a "way" to get the beam and now I see it will have to be short range weapon, maybe a few might minutes. BTW, I am going to propose a antineutron beam that decays into antimatter protons assuming the antineutrons have a similar half life to matter neutrons. Now I just have to propose a "magic" to turn a coherent proton beam into antineutrons on the fly! I think I'll name it a gravitational reverse charge pinch! Thanks again!

Edited May 24 by Moontanman

[KJW]

39 minutes ago, swansont said:

They tend to increase the binding energy per nucleon of nuclei, which one would interpret as an attraction. Also, mirror nuclei (same number of nucleons by neutron and proton number switched) show that all the nucleons attract each other in the same way.

The interaction has a limited range, though.

You can’t form a stable nucleus with just neutrons, or mostly neutrons, though, because it’s energetically favorable for neutrons to decay into protons in those situations.

You appear to be talking about the strong force. But is there the nuclear equivalent of electromagnetic van der Waals forces that would also lead to attraction?

 

 

Edited May 24 by KJW

[Moontanman]

I want to say that why I am asking this question is the idea of writing a story based on as few "magical" technologies as possible. One of my fav writers, Vernor Vinge, wrote a series called "Across Real Time" that is based on only one such technology called a "bobble" the sweep of the story is amazing and I want to stay as close to that ideal as possible in the story I am considering.   

[swansont]

2 hours ago, KJW said:

You appear to be talking about the strong force. But is there the nuclear equivalent of electromagnetic van der Waals forces that would also lead to attraction?

vdW forces are from induced dipoles where there are + and - charges, and you don’t have that here.

But there’s a lot more to this; you’re obviously not getting the whole thing in a few sentences. Spin has an effect, for example. The dynamics of the interaction vary depending on whether you’re looking inside of a nucleon or between nucleons. This isn’t a deep dive into any of that.

[TheVat]

1 hour ago, Moontanman said:

I want to say that why I am asking this question is the idea of writing a story based on as few "magical" technologies as possible. One of my fav writers, Vernor Vinge, wrote a series called "Across Real Time" that is based on only one such technology called a "bobble" the sweep of the story is amazing and I want to stay as close to that ideal as possible in the story I am considering.  

When I read it back in the late 80s, Marooned in Realtime fairly blew my mind.  That's one for me to reread.  One of the best conceptual writers - I liked Fire Upon the Deep, too.  Died this March - too soon.

Am curious what led you to neutrons, for a beam weapon.  Protons not good enough for you?  😀

 

[MigL]

3 hours ago, KJW said:

But is there the nuclear equivalent of electromagnetic van der Waals forces that would also lead to attraction?

Yes.
Essentially, the strong nuclear force that binds nucleons together in the nucleus, is 'residual' color force which binds quarks in the nucleon.
It is obviously not the same mechanism as VdW forces, but it is similar in that VdW can be considered 'residual' electromagnetic force.

[Moontanman]

10 hours ago, TheVat said:

When I read it back in the late 80s, Marooned in Realtime fairly blew my mind.  That's one for me to reread.  One of the best conceptual writers - I liked Fire Upon the Deep, too.  Died this March - too soon.

Am curious what led you to neutrons, for a beam weapon.  Protons not good enough for you?  😀

 

Protons can be defeated by a magnetic field, neutrons cannot, anti neutrons are even better when they contact matter, due to the half life of the neutrons it should create some interesting effects, like the beam being visible, and the the point of contact being a continuous multi megaton explosion. It should leave behind an expanding cloud of anti hydrogen if I understand neutron decay correctly. This would have to be a space weapon, no handheld anti neutron beam weapons! 

I am thinking of a beam that puts a microgram of antimatter on the target every micro second. Space operas illustrated by AI are becoming popular on you tube, I've already had one story published this way and I am hoping for others. No money in it but its still fun to hear your own words being narrated over AI images.  

I didn't know Vernor Vinge had died, his level of genius is a distant goal but it shines bright as a guiding star. BTW anyone who follows the erotic story (Slave girl Patty) on my blog I have two more chapters published!

[KJW]

12 hours ago, swansont said:

vdW forces are from induced dipoles where there are + and - charges, and you don’t have that here.

But there’s a lot more to this; you’re obviously not getting the whole thing in a few sentences. Spin has an effect, for example. The dynamics of the interaction vary depending on whether you’re looking inside of a nucleon or between nucleons. This isn’t a deep dive into any of that.

11 hours ago, MigL said:

Yes.
Essentially, the strong nuclear force that binds nucleons together in the nucleus, is 'residual' color force which binds quarks in the nucleon.
It is obviously not the same mechanism as VdW forces, but it is similar in that VdW can be considered 'residual' electromagnetic force.

I think I should clarify my question.

I know that the strong force binds quarks within nucleons, and that the binding between nucleons is due to the residual strong force similar to the van der Waals force between neutral atoms or molecules. However, this was not what I meant by "the nuclear equivalent of electromagnetic van der Waals forces". Neutrons have both positive and negative electromagnetically charged quarks, and therefore it is not unreasonable to consider if there exists an induced electric dipole to induced electric dipole attractive force that is similar to the van der Waals force. That is, the attractive force between neutrons I was enquiring about was electromagnetic and the result of an induced charge distribution within the neutrons.

 

 

[swansont]

4 hours ago, KJW said:

I think I should clarify my question.

I know that the strong force binds quarks within nucleons, and that the binding between nucleons is due to the residual strong force similar to the van der Waals force between neutral atoms or molecules. However, this was not what I meant by "the nuclear equivalent of electromagnetic van der Waals forces". Neutrons have both positive and negative electromagnetically charged quarks, and therefore it is not unreasonable to consider if there exists an induced electric dipole to induced electric dipole attractive force that is similar to the van der Waals force. That is, the attractive force between neutrons I was enquiring about was electromagnetic and the result of an induced charge distribution within the neutrons.

The dipole moment depends on the charges and their separation. The separation would be small, since the particles are. ~5 orders of magnitude smaller than in atomic systems. The charges are smaller, too, so you’d have a smaller moment because of that.

[KJW]

16 hours ago, swansont said:

The separation would be small, since the particles are. ~5 orders of magnitude smaller than in atomic systems.

This would also allow the neutrons to approach each other ~5 orders of magnitude closer than in atomic systems.

 

 

[swansont]

2 hours ago, KJW said:

This would also allow the neutrons to approach each other ~5 orders of magnitude closer than in atomic systems.

Why does it matter? The strong interaction is already stronger than the electrostatic, dipole interactions are weaker, and induced dipole interactions weaker still. vdW forces only matter when you have a neutral particle, so there is no direct force of attraction, which isn’t the case here. It would be a tiny correction to the binding energy, assuming it’s not zero.

And it would probably only be a (small) factor if you only had a small number of nucleons, because with more the effects would tend to cancel. Deuterium, Helium and perhaps Lithium and Beryllium. Once you have nucleons on both sides of your target, symmetry cancels all this out.