Talk:Nuclear force

From Wikipedia, the free encyclopedia

WikiProject Physics This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.
??? This article has not yet received a rating on the assessment scale. [FAQ]
??? This article has not yet received an importance rating within physics.

Help with this template Please rate this article, and then leave comments to explain the ratings and/or to identify its strengths and weaknesses.

Contents

[edit] Illert

Someone with a real axe to grind has added several paragraphs about Chris Illert's nuclear models. Personally, I'm not familiar with that work (this is very much not my field), but the current writing style has no place in a neutral POV encyclopedia. It contains screeds comparing the entire community of nuclear physicists to medieval alchemists. I'm deleting them. If anyone can write something about these alternative models from a neutral POV, feel free to add them back. -Dave —Preceding unsigned comment added by Nucleardave (talk • contribs) 14:06, 18 October 2007 (UTC)

[edit] Overwhelming

Ahhhhh, you know you're on Wikipedia when you need a physics(also known as madar chod) degree to understand a relatively straight forward topic like the Strong Nuclear Force.Diafel 06:44, 11 March 2006 (UTC)

I agree completely. Two sentences of introduction then BAM: Yukawa potentials, pions, quantum chromodynamics... while I've no doubt this information belongs SOMEWHERE in the article, it has no place in the introduction. Bear in mind the audience of this article: IIRC, the nuclear force is introduced as a concept at high school level. The material should start simple and general and ease into the details. As things stand, no-one without the requisite physics degree-level jargon will make it past the intro. And if you do have a physics degree, you're unlikely to be reading an encyclopedia article on such a basic concept. Think of the children, dammit!

It's looking better now, but one more suggestion: the paragraph in the intro discussing the recent change in terminology is too detailed and uses jargon which has no place in the intro. There should be a brief, simple sentence or two pointing out that the old "strong" usage has been dropped - this is important to get across in the intro - and the details of the confusion, involving QCD etc. should be in their own section near the end of the article. That would make it heaps clearer, while keeping all the present content.

[edit] Residual strong force

I made Residual strong force REDIRECT to Nuclear force. This IS correct, right? I hardly find this stuff easy going. :-) - Writtenonsand 13:25, 17 January 2006 (UTC)

Yes that is correct. linas 18:19, 17 January 2006 (UTC)

[edit] Rename article

Maybe we should rename this article to Stronge Nuclear Force instead. This helps to distinguish this force from the weak nuclear force and is more well-known nowadays. (unsigned, anonymous, 8 Feb 2006)

Yes, good idea. Maybe an admin can do this for us. linas 05:21, 9 February 2006 (UTC) Retract per below. linas 00:49, 10 February 2006 (UTC)
I disagree. The nuclear force is not confused with the weak interaction and is not the same as the strong residual force (though it is caused by residue of the strong interaction); it is specifically the force felt between nucleons. Compare modern usage: an arXiv search for "nuclear force" in modern literature (136 uses), "strong nuclear force" (3 uses), "weak nuclear force" (6 uses). Clearly, the preferred term is "nuclear force". -- Xerxes 15:08, 9 February 2006 (UTC)
Oh, ok. (If I was good at naming things, I would have majored in biology). linas 00:49, 10 February 2006 (UTC)

[edit] Nuclear stability

I'm not an expert on this stuff, but a back of the envelope calculation shows that the repulsive Coulomb force between two protons at a distance of 1.3fm is about 140N. This being the case, is the figure of 104N for the nuclear force a typo?

[edit] Pions or Gluons

Which particles are exchanged as part of the nuclear force? I always thought it was gluons, but the article says pions. VxP 15:38, 5 December 2006 (UTC)

Read the first paragraph instead. If by "nuclear force" you mean the force between nucleons, it's best understood as an exchange of virtual mesons (pi's and rho's). Of course these things are made of quark-antiquark pairs plus gluons, so in that sense the quarks serve as mashed potatoes to carry a residual bit of gluon gravy (the QCD or color force or honest-to-god strong force) between nucleons. You can think of forces between nucleons as a little bit like the van der Waals forces between neutral atoms like helium. The atoms are neutral overall, but self-polarization causes a little bit of electromagnetic interaction between them anyway. In the same way, nucleons are "colorless" or QCD white, but when they are close together, the gluons find a way to make a little interaction anyway, via the tricky path of getting the vacuum to polarize into virtual quark-antiquark pairs (those virtual mesons, the pi's and rho's), and when those go out, they can take virtual gluons with them. These gluons, in a sense, underlie the inter-nuclear force in the same way that electron-proton forces (i.e., electrostatic forces mediated by virtual photons) underlie van der Waals interactions between neutral atoms.

Or so I've been told. Caveat is I have to give you my metaphorical picture because the math is quite beyond me. However, I have it on authority of people who can do the math that this is sometimes the mental picture they use. SBHarris 19:38, 5 December 2006 (UTC)

Thanks, that's the most accessible explanation I've read anywhere! VxP 20:18, 5 December 2006 (UTC)

[edit] charge independence and dineutrons

this article says that the residual nuclear force is nearly independent of charge. the article on dineutrons says that there are not bound pairs of neutrons. It seems to me that something should be added to this nuclear force article about the residual nuclear attraction between a pair of neutrons, and between a pair of protons, as opposed to the attraction between a proton and a neutron. I have not found information about whether a pair of protons (Helium-2, no neutrons) is a bound state with short lifetime, or not a bound state. I assume that the short lifetime of the neutral pi meson relative to the charged pi meson gives reason to why a pair of neutrons are not a bound state (and maybe a pair of protons is not a bound state). at any rate, it isn't simply that NN, NP, and PPs are strongly attracted to one another, nearly equally, is it? isn't the neutron-proton attraction much stronger than neutron-neutron and proton-proton?

(I have found the Wikipedia physics articles very helpful and interesting. I am not a physicist.) PhysicsStudent 17:10, 6 January 2007 (UTC)

Quoting excerpt from book, Amit Goswami [of University of Oregon], The Concepts of Physics, published by D. C. Heath, 1979, no edition number specified, ISBN 0-669-01897-X -- "But we may wonder why nuclei are not just bundles of neutrons alone. Why have the proton at all with its problem of electrical repulsion? The answer is that the attractive nuclear force between neutrons and protons is the strongest (stronger than the nuclear attraction between a pair of protons or a pair of neutrons). Because of this there is a tendency for nuclei to have an equal number of protons and neutrons." Mike Lepore, Stanfordville, New York 16:57, 6 March 2007 (UTC)
It might be helpful (here and on dineutron) to state the relative strengths of the N-P, P-P, N-N nuclear force. Rod57 03:26, 9 November 2007 (UTC)
Just to set the record straight. there is no difference in the strengths of the N-N, N-P, P-P nuclear interactions. (One can only assume that the Amit Goswami book is either mistaken or misquoted). To Understand the reason why there are no bi-neutron or bi-proton states one has to go a little deeper into the theory. Without going into any details, I will only say here that Pauli's exclusion principle plays a role here (protons and neutrons are fermions and must obey Pauli's principle). In a di-proton or di-neutron one would have the biding of two identical particles. By Pauli's principle these particles could not be in a symmetric state. one of them would have to be forced into a higher energy level. this extra energy is just enough to render these states unbound. Dauto (talk) 17:45, 21 January 2008 (UTC)

[edit] Mesons or Quarks and Gluons?

When I researched the nuclear force on the Internet, I found a source that said that the residual strong force actually occurred via exchange of quarks and gluons, not mesons.--67.10.200.101 02:00, 7 July 2007 (UTC)

I think that it is fair to say that at nuclear distances, it is a grey region as to whether there are quarks and gluons or mesons and baryons. What is written seems like a fair representation of current knowledge, although it is a bit technical. The description doesn't really say what is mediating the force (which is subjective) and merely gives the properties of the nuclear potential. jay 02:39, 7 July 2007 (UTC)

[edit] 1/r^7 Potential

I posted that this fact needed a reference several months back and no one has tracked it down. I do not believe that it is correct because in order to have a power-law potential you need to have a long ranged field; however, QCD has a mass gap. With no long ranged fields, the potential has to fall off exponentially at long distances. If this is only valid at short distances, which distances and what makes up the units (m_N or m_pi)? This fact has been quoted in other wikipedia articles in contexts where it isn't right. jay 15:02, 7 July 2007 (UTC)

[edit] Non-conservation of orbital angular momentum

Article says:

The NN force has a noncentral or tensor component. This part of the force does not conserve orbital angular momentum, which is a constant of motion under central forces.

Can somebody explain why is that so? And can nuclear force realy violate law of conservation of angular momentum?

And linking to tensor article does not help the reader to understand the subject any better. It should be either explainded, or linked in better way. --83.131.19.126 (talk) 18:06, 27 December 2007 (UTC)

It's talking about orbital angular momentum of the object in orbit only, not the total of the system, which of course is conserved. Think of an object stuck in a whirlpool. Not only would it feel a central force pulling it toward the center of the whirlpool, but also a radial force which pushes it faster the closer in it goes. That's a good example of a force which doesn't conserve angular momentum for the orbiting object-- it goes much faster than it would from just angular momentum conservation laws, because it gains angular momentum from the fluid.

If you want a gravity example, consider that the moon doesn't perfectly conserve angular momentum of orbit, because it spirals outward with time. In compensation, the rotation of the Earth decreases in rate. Total angular momentum is conserved, but orbital angular momentum isn't. The total force which acts on the moon is not a perfectly central force because such a force would have no place for a component that (like a rocket pushing in the direction of the moon's motion) increases the total energy of the moon in its orbit via this mechanism of angular momentum transfer, and would do so even if the orbit started out circular. Spiral orbits (inward or outward) can't be produced by simple central forces (think of the inward spiral of a satellite produced by air friction).

For nucleons, the spins of the nucleons contribute hugely to the forces produced (they need to be parallel to give the best force and for two neutrons that forces one into a higher energy state as noted above), so nuclear forces are a bit like (pairs of) whirlpools, with a vengeance. SBHarris 19:03, 21 January 2008 (UTC)

[edit] merge?