Do Protons and Neutrons Move around in the Nucleus?

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Discussion Overview

The discussion centers around the movement and arrangement of protons and neutrons within the atomic nucleus, particularly in the context of a helium atom. Participants explore whether these nucleons can change positions, how they vibrate, and the implications of classical versus quantum mechanical models of the nucleus.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants propose that protons and neutrons vibrate in place but question whether they can change positions within the nucleus.
  • Others argue that classical models of nucleon arrangement are inadequate, suggesting that the nucleus does not behave like a classical system.
  • A participant mentions that if nucleons were to vibrate classically, the helium-4 nucleus would exhibit an electric dipole moment, which it does not, implying a spherically symmetric charge distribution.
  • There is a discussion about the concept of nucleons existing in energy levels similar to electrons in atomic orbitals, with some participants affirming this idea while noting the complexity of nuclear shapes.
  • Participants mention that the identity of individual nucleons is lost in quantum mechanics, and that scattering experiments cannot reveal their specific arrangements.
  • Some contributions highlight that nuclear shapes are complicated and can be non-spherical, with references to specific isotopes and their properties.
  • There is a suggestion that the internal arrangement of a nucleus cannot be defined in the same way as electron spins in a singlet pair.
  • One participant notes that while nucleons may have a shell structure, it is complex and differs from the simpler models used for electrons.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the movement and arrangement of nucleons within the nucleus. There is no consensus on whether classical models can adequately describe these phenomena, and the discussion remains unresolved with various hypotheses presented.

Contextual Notes

Limitations include the dependence on classical versus quantum mechanical interpretations, the complexity of nuclear shapes, and the unresolved nature of how nucleons are arranged within the nucleus.

  • #31
stedwards said:
Of, course, how foolish of me.
That would be very nice to see.

I did a short search on images of "nuclear orbitals" and came up empty. Do you have anything like this? It would be fairly in line with the OPs initial question.

See above. :wink:

I've never seen a "picture" of nuclear orbitals like the ones you see for atoms (e.g. http://www.sccj.net/publications/JCCJ/v5n3/a81/fig1.gif) although there is a relationship - you have the same angular momentum coupling in nuclei too, but there's ... more - you can't ignore spin-orbit coupling, for starters. The picture that comes to my mind would be the Nilsson model, showing the single particle energy levels for nucleons:
fig1.png


Where ##\beta## is the deformation of the nucleus. Then, you can realize that these are single-particle levels, and you can then build a rotational band on top of each of these. You can then compare that to a set of atomic energy levels.

But this is way more intimidating than is actually educational, unless you're already familiar with this sort of thing. o_O

(ETA - each number there is a number of nucleons. Solid vs dashed lines indicate parity. The colours indicate subshells)
 
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  • #32
e.bar.goum said:
See above. :wink:
You're very kind.
I've never seen a "picture" of nuclear orbitals like the ones you see for atoms (e.g. http://www.sccj.net/publications/JCCJ/v5n3/a81/fig1.gif) although there is a relationship - you have the same angular momentum coupling in nuclei too, but there's ... more - you can't ignore spin-orbit coupling, for starters. The picture that comes to my mind would be the Nilsson model, showing the single particle energy levels for nucleons:
fig1.png


Where ##\beta## is the deformation of the nucleus. Then, you can realize that these are single-particle levels, and you can then build a rotational band on top of each of these. You can then compare that to a set of atomic energy levels.

But this is way more intimidating than is actually educational, unless you're already familiar with this sort of thing. o_O

Not at all educated on nuclear physics(!), which is why us, unfamiliar with the discipline, like pictures--at least, I do. In searching "Nilsson model" I did find one apparently relevant pictorial, prepending an http://ns.ph.liv.ac.uk/~esp/lectures/PHYS490/Phys490.pdf for a class course in what appears to be Liverpool.
 
  • #33
stedwards said:
You're very kind.Not at all educated on nuclear physics(!), which is why us, unfamiliar with the discipline, like pictures--at least, I do. In searching "Nilsson model" I did find one apparently relevant pictorial, prepending an http://ns.ph.liv.ac.uk/~esp/lectures/PHYS490/Phys490.pdf for a class course in what appears to be Liverpool.

HAH! Your link kicked something in my mind. Naturally, you can get these kind of pictorial representations in TDHF calculations! I have slides showing 16O states! Unfortunately, it's not something I have online. But, here are a selection of examples. These show density.
Screenshot from 2015-07-06 15:29:55.png


Screenshot from 2015-07-06 15:29:55.png
Screenshot from 2015-07-06 15:30:14.png
Screenshot from 2015-07-06 15:30:48.png
Screenshot from 2015-07-06 15:30:54.png
Screenshot from 2015-07-06 15:31:11.png
 
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  • #34
Nice.

They are very peculiar, and not at all like superpositions of s, p, d, f electron orbitals, with weirdly, less symmetry.

Are they derived theoretically or from experimental data?

Of course, experimental data is interpreted through theory, but what I mean to ask is---I'm not really sure how to put it. Maybe you can enlighten me.
 
Last edited:
  • #35
stedwards said:
Nice.

They are very peculiar, and not at all like superpositions of s, p, d, f electron orbitals, with weirdly, less symmetry.

Are they derived theoretically or from experimental data?

Like I said, they're TDHF calculations for 16O. I don't know that you could get these from experiment - nuclear shapes are the sum of all of these orbitals. However, the input nuclear force for this particular simulation is derived from experimental data. (For the experts, it's Skyrme SLy6). Now, a valid question would be -- "how well does TDHF, being a mean field approximation, reproduce the shapes of orbitals?", to which my answer is, I've no idea. :sorry:
 
  • #36
Wait, did some one start a new thread for the different question?
Vanadium 50 said:
Are you saying it's a different question entirely? Then you should start a new thread.
 
  • #37
RaulTheUCSCSlug said:
Wait, did some one start a new thread for the different question?
I don't think so.
 
  • #38
NIce
 
  • #39
It's also worth pointing out that it is predicted that amongst the neutral pions that mediate between the neutrons and protons, there are charged pions that would turn a neutron into a proton and a proton into a neutron (e.g. a neutron (udd) emitting a negative pion (dū) becomes a proton (uud) and the proton absorbing the negative pion becomes a neutron). Some sources predict the protons and neutrons '..are constantly in flux, changing state every 10-23 seconds..'.

Sources-
Pions
Structure of the Nucleon: Pions and Quarks (section 'Three types of pions')
Introductory Nuclear Physics page 94
 
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  • #40
The interaction can be given under the assumption that the forces are derivable from a potential which depends upon the relative spin orientation of the particles but apparently not upon whether they are protons or neutrons. In order to obtain some insight into the binding of the nucleus, we assume the simplest possible forces and test the consequences of these assumptions by experiment.
 
  • #41
In any model assumed the energy level gaps have to be millions of times more I think.Any readjustnents among nucleons must invove titanic effects in reference to atom overall.It is evident due to radiations like gamma rays emitted.
 

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