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Silly question, I'm sure, but: Why do we think that nuclei contain distinct neutrons and protons at all, rather than simply being conglomerations of Up and Down

Silly question, I'm sure, but: Why do we think that nuclei contain distinct neutrons and protons at all, rather than simply being conglomerations of Up and Down quarks with the constraint that color charge must be zero and electrical charge must be integral?

AstralStorm 8y ago
Because they do not break apart into quarks, but nucleons. That was the ELI5 version if you have a particle accelerator. Additional evidence includes phonons - behavior of crystals in nonlinear optics, semiconductivity in doped crystals. (Partial credit if you thought of concept of electron gas.)
- cperciva 8y ago
  That seems like a non-answer. Uranium often breaks apart into Barium and Krypton, but nobody ever suggests that those Uranium atoms contained Barium and Krypton atoms.
  - AstralStorm 8y ago
    Uranium loses "unexplained" unaccounted for mass other than leaving behind Barium and Krypton. ELI5 continuing. What is that mass? What are its properties if you capture enough of it? Does it behave like "a mass of quarks"? Does it behave like an element? What are the constraints on that mass? It's funny that I have to talk about electroweak interactions to a guy who knows what a quark is. Perhaps they also know what a boson and fermion are. The entity known as neutron has an interesting property that causes a different set of bosons to be emitted when it's broken out than as if just random quarks were torn out. The color constraint does not explain it.
deleted 8y ago
[deleted]
raattgift 8y ago
Does this help as a starting point? http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/scatele.html#c1 http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/scatele.h...
- cperciva 8y ago
  Yes, I think that answers my question -- if I'm reading it right, the scattering behaviour of low-energy electrons indicates that they're hitting something "proton-like" rather than something "quark-like" inside the nucleus?
  - ahazred8ta 8y ago
    Yes, exactly. At low energies we can see that most of the atom's mass is in a nucleus. At medium energies we see that there are proton and neutron sized lumps in the nucleus. At very high energies we can see that the protons etc have quark sized lumps inside them. (Full disclosure: FWIW I took a physics course from one of the professors on the team which discovered gluons.)
  - raattgift 8y ago
    Yes. Nucleons and quarks represent internal degrees of freedom (DoFs) inside the nucleus resp. proton that can receive momentum-energy from a scattering electron. This is measured as a loss of the sum of the kinetic energies of the electron and its target. At low energies, the transfer to internal DoFs is negligible, so the scattering is elastic. At higher energies the transfer is relatively large, so the scattering is inelastic. At sufficiently high energy, the nucleus disintegrates into components and new particles, and in the target's centre-of-momentum frame the sum of all their kinetic energies matches the change of the electron's. But at even higher energy there is again an apparent loss of kinetic energy, so there must be further internal DoFs within the components. Those are in the proton. The higher energy scatterings are "deep". As one does deep inelastic scattering, the proton's internal DoFs absorb electron momentum-energy. At sufficiently high energy levels the proton disintegrates into many new particles. There are also differences in the scattering angle -- the amount by which the scattered electron is deflected from its beam path. Scattering angles are low in elastic scattering, and high in inelastic scattering. This gives further information about the internal DoFs. For more see Mott scattering, deep inelastic scattering, and the parton model.
jcranmer 8y ago
I'm not totally versed in the physics of the situation, but the primary evidence here is that there is a massive difference in the force needed to break a nucleus into nucleons and the force needed to break a nucleus into quarks (well, non-proton/neutron quark aggregations). This suggests that there is intermediate structure inside the nuclei.
mncharity 8y ago
Not my field, so I'll leave others to answer. But there's also further clumping. In light nuclei, nucleons are clustered as 4alpha particles (two protons and two neutrons). Simulation has ground-state 8Beryllium mass density shaped like a dumbbell of two alphas. And ground-state 20Neon shaped like a 10 femtometer ball-and-stick old wine bottle.[1] With a triangle of alphas (like non-ground-state C), a forth making a tetrahedron (like non-ground-state O), and the fifth hanging further out on the opposite side. Research for an old project. For improving introductory material science in early-primary school. Instead of the usual "just memorize the words - we don't teach those atoms things until the year after next", or the reform "teach atoms up", I was exploring "teach nucleons up". Atoms approached from the perspective of nuclei. Building out from the familiar, almost-classical marbles, rather than attempting to stand on a foundation of the least-intuitive utterly-bizarre wacky electrons. But I didn't manage to get much conversation/collaboration going.[2] :/ The traditional and common graphical representations of nuclei in education are very aphysical. [1] http://www.clarifyscience.info/assets/2017-Atoms/assets0/wk/1406.2473-Ne.png http://www.clarifyscience.info/assets/2017-Atoms/assets0/wk/... [small image] from https://arxiv.org/abs/1406.2473 https://arxiv.org/abs/1406.2473 page 4. https://arxiv.org/abs/1802.02873 https://arxiv.org/abs/1802.02873 is more recent, but only Ne. [2] http://www.clarifyscience.info/part/Atoms http://www.clarifyscience.info/part/Atoms is a crufty slowwwwwly-loading page (wasn't intended to be public), I wrote in support of a couple of exploratory conversations.

AstralStorm 8y ago

Because they do not break apart into quarks, but nucleons. That was the ELI5 version if you have a particle accelerator. Additional evidence includes phonons - behavior of crystals in nonlinear optics, semiconductivity in doped crystals. (Partial credit if you thought of concept of electron gas.)

cperciva 8y ago
That seems like a non-answer. Uranium often breaks apart into Barium and Krypton, but nobody ever suggests that those Uranium atoms contained Barium and Krypton atoms.
- AstralStorm 8y ago
  Uranium loses "unexplained" unaccounted for mass other than leaving behind Barium and Krypton. ELI5 continuing. What is that mass? What are its properties if you capture enough of it? Does it behave like "a mass of quarks"? Does it behave like an element? What are the constraints on that mass? It's funny that I have to talk about electroweak interactions to a guy who knows what a quark is. Perhaps they also know what a boson and fermion are. The entity known as neutron has an interesting property that causes a different set of bosons to be emitted when it's broken out than as if just random quarks were torn out. The color constraint does not explain it.

deleted 8y ago

[deleted]

raattgift 8y ago

Does this help as a starting point? http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/scatele.html#c1 http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/scatele.h...

cperciva 8y ago
Yes, I think that answers my question -- if I'm reading it right, the scattering behaviour of low-energy electrons indicates that they're hitting something "proton-like" rather than something "quark-like" inside the nucleus?
- ahazred8ta 8y ago
  Yes, exactly. At low energies we can see that most of the atom's mass is in a nucleus. At medium energies we see that there are proton and neutron sized lumps in the nucleus. At very high energies we can see that the protons etc have quark sized lumps inside them. (Full disclosure: FWIW I took a physics course from one of the professors on the team which discovered gluons.)
- raattgift 8y ago
  Yes. Nucleons and quarks represent internal degrees of freedom (DoFs) inside the nucleus resp. proton that can receive momentum-energy from a scattering electron. This is measured as a loss of the sum of the kinetic energies of the electron and its target. At low energies, the transfer to internal DoFs is negligible, so the scattering is elastic. At higher energies the transfer is relatively large, so the scattering is inelastic. At sufficiently high energy, the nucleus disintegrates into components and new particles, and in the target's centre-of-momentum frame the sum of all their kinetic energies matches the change of the electron's. But at even higher energy there is again an apparent loss of kinetic energy, so there must be further internal DoFs within the components. Those are in the proton. The higher energy scatterings are "deep". As one does deep inelastic scattering, the proton's internal DoFs absorb electron momentum-energy. At sufficiently high energy levels the proton disintegrates into many new particles. There are also differences in the scattering angle -- the amount by which the scattered electron is deflected from its beam path. Scattering angles are low in elastic scattering, and high in inelastic scattering. This gives further information about the internal DoFs. For more see Mott scattering, deep inelastic scattering, and the parton model.

jcranmer 8y ago

I'm not totally versed in the physics of the situation, but the primary evidence here is that there is a massive difference in the force needed to break a nucleus into nucleons and the force needed to break a nucleus into quarks (well, non-proton/neutron quark aggregations). This suggests that there is intermediate structure inside the nuclei.

mncharity 8y ago

Not my field, so I'll leave others to answer. But there's also further clumping. In light nuclei, nucleons are clustered as 4alpha particles (two protons and two neutrons). Simulation has ground-state 8Beryllium mass density shaped like a dumbbell of two alphas. And ground-state 20Neon shaped like a 10 femtometer ball-and-stick old wine bottle.[1] With a triangle of alphas (like non-ground-state C), a forth making a tetrahedron (like non-ground-state O), and the fifth hanging further out on the opposite side. Research for an old project. For improving introductory material science in early-primary school. Instead of the usual "just memorize the words - we don't teach those atoms things until the year after next", or the reform "teach atoms up", I was exploring "teach nucleons up". Atoms approached from the perspective of nuclei. Building out from the familiar, almost-classical marbles, rather than attempting to stand on a foundation of the least-intuitive utterly-bizarre wacky electrons. But I didn't manage to get much conversation/collaboration going.[2] :/ The traditional and common graphical representations of nuclei in education are very aphysical. [1] http://www.clarifyscience.info/assets/2017-Atoms/assets0/wk/1406.2473-Ne.png http://www.clarifyscience.info/assets/2017-Atoms/assets0/wk/... [small image] from https://arxiv.org/abs/1406.2473 https://arxiv.org/abs/1406.2473 page 4. https://arxiv.org/abs/1802.02873 https://arxiv.org/abs/1802.02873 is more recent, but only Ne. [2] http://www.clarifyscience.info/part/Atoms http://www.clarifyscience.info/part/Atoms is a crufty slowwwwwly-loading page (wasn't intended to be public), I wrote in support of a couple of exploratory conversations.