Proton Radius: Is it a Sphere or Shell?

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Discussion Overview

The discussion revolves around the nature of the proton's radius and its implications for understanding the structure of protons, particularly whether it can be considered a sphere, a shell, or something else entirely. Participants explore theoretical concepts, the behavior of quarks, and the implications of the strong nuclear force.

Discussion Character

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

Main Points Raised

  • One participant suggests that the proton's radius (~10e-15 m) could be analogous to an electron's orbital density cloud, questioning if it represents a bounding volume, an energy barrier, or a surrounding shell.
  • Another participant proposes that the radius serves as an approximate limit beyond which the strong nuclear force becomes significant, indicating that getting closer than 1 femtometre involves the binding of quarks.
  • A different participant notes that there is a further drop in the strong force when approaching 0.1 fermi, suggesting a complex behavior of the force at very short distances.
  • One participant explains that the quarks in a proton exhibit a wave function similar to that of electrons in an atom, emphasizing that there is no definite boundary like a physical surface.
  • Another participant references the concept of the "charge radius" of the proton, defined mathematically, and mentions that the wave function is approximately spherical.
  • There is a mention of the strong force becoming repulsive at very close distances, with a reference to its implications in astrophysical phenomena like supernovae.
  • A participant shares links to articles that explore the possible shapes of a proton and its quarks, indicating ongoing research in this area.

Areas of Agreement / Disagreement

Participants express various viewpoints on the nature of the proton's radius and the behavior of the strong force, indicating that multiple competing views remain without a clear consensus.

Contextual Notes

The discussion includes references to specific measurements and theoretical constructs, but there are limitations in the assumptions made about the nature of the strong force and the interpretation of the proton's structure.

neurocomp2003
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a proton is given a radius...i think its ~10e-15
since a proton is uud is this "radius" like [1]a electron orbital density cloud that is said to be in atoms...that is to say that its a bounding volume(ie in computer geometry) or [2]an energy barrier on the uud of this radius size? Or [3]there is a shell that surrounds the uud?
 
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I think it is just an approximate limit beyond which the strong nuclear force becomes significant. In other words, get closer than about 1 femtometre and you're into the range at which the quarks bind together. Beyond that, the strength of the strong force drops off rapidly.
 
There's another really interesting aspect:get closer than 0.1 fermi and the strong force drops again...

Daniel.
 
The quarks in a proton have the same type of wave function as the electrons iin an atom. There is no definite boundary like the surface of the Earth.
The "charge radius" of the proton is defined as the square root of the expectation value <\rho r_2>=<\sum q_i r_i^2>, summed over the 3 quarks.
This rms charge radius is about 0.8 fm. The wave function is approximately spherical, corresponding to L=0 for the orbitals.
 
dextercioby said:
There's another really interesting aspect:get closer than 0.1 fermi and the strong force drops again...

Daniel.
...and becomes repulsive, no? Like in the iron-core-rebound which is responsible for some types of supernovae?
 

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