7 ms·

Why neutrons and protons are modified inside nuclei

90 points by lainon 8y ago

Leace 8y ago
The article on Semi-empirical mass formula [0] is also interesting read, especially deconstructing the formula and seeing what impact each term has (e.g. asymmetry term and the difference between the relation of number of protons to the number of neutrons). [0]: https://en.wikipedia.org/wiki/Semi-empirical_mass_formula https://en.wikipedia.org/wiki/Semi-empirical_mass_formula
- Leace 8y ago
  An interesting fact: free neutrons [0] are unstable and will decay into protons [1] with mean lifetime of ~15 minutes. That is one down quark will decay into an up quark (neutron is composed out of udd quarks, proton: uud) because down quarks have bigger mass than up quarks (see this nice Feynman diagram [2]). In the nucleus on the other hand Pauli exclusion principle makes two protons less favorable than a proton and neutron. Warning: this is what I understood from Wikipedia, IANAP (I am not a physicist). [0]: https://en.wikipedia.org/wiki/Neutron https://en.wikipedia.org/wiki/Neutron [1]: And a couple of other particles, see: https://en.wikipedia.org/wiki/Neutron#Description https://en.wikipedia.org/wiki/Neutron#Description [2]: https://commons.wikimedia.org/wiki/File:Beta_Negative_Decay.svg https://commons.wikimedia.org/wiki/File:Beta_Negative_Decay....
DiseasedBadger 8y ago
Does this draw into question whether there is such thing as a "nuclear field"?
- teilo 8y ago
  No. The "nuclear field" is just a term for the composite field resulting from the constituent particles of the nucleus (the quarks and gluons) and their interaction. For there to be no "nuclear field" there would have to be no nucleus. Well, that's not entirely correct, because particle fields permeate all of space. To grossly simplify, there's something happening in those fields in a nucleus. The various particle fields are vibrating and interacting. "Nuclear field" is just shorthand for this interaction that is the result of the presence of the particles of the nucleus. The result described in this article just rules out the nuclear field as being responsible for the EMC effect.
- andrepd 8y ago
  How do you mean?
criddell 8y ago
This is offtopic, but do neutrons and protons have a similar dual wave / particle nature like photons do? What about quarks and all the sub-particles?
- dmitrygr 8y ago
  Everything acts like a wave. The term to Google for is "de broglie wavelength". Even you have an effective wavelength and you refract (slightly) when passing through a slit (door)
  - criddell 8y ago
    My brain just can't accept that. It's seems too nuts. What does mass mean when you are talking about waves and fields? What does it mean to collide two waves together and look for smaller waves coming out? Everything is divisible? Or is there some kind of Planck wavelength?
    - trentlott 8y ago
      You might be interested in Pilot Wave Theory. It tries to reconcile wave/particle duality by claiming there is a real physical particle at all times in an attempt to get around the strange idea of everything being a probablistic wavefunction (the Copenhagen interpretation). It explains some things pretty intuitively (double slit experiment), but from what I can tell it becomes too convoluted for other things. Mass can be related to energy with E=mc^2, and you can get some idea of its relation to wavelength and wave collisions. I think a smallest wavelength is unlikely, because it would put an upper bound on energy. The only side-effect of increasing the energy density (ie a lot of energy in a small space, like a very low-wavelength photon) is the formation of a black hole. I think the question of whether photons (massless) can form them is one of those quantum-gravity issues that are awaiting a theory.
      - perl4ever 8y ago
        "You might be interested in Pilot Wave Theory. It tries to reconcile wave/particle duality by claiming there is a real physical particle at all times in an attempt to get around the strange idea of everything being a probablistic wavefunction (the Copenhagen interpretation)." I don't understand much of anything, but based on what I read, I strongly prefer the idea that everything is a field and particles don't exist, rather than vice versa. It just feels right. We don't experience particles any more than waves in our daily lives anyway.
trentlott 8y ago
I want to take a second to rep my absolute favorite podcast, Physics Frontiers.° It's not a "pop-sci" podcast - they take a couple of interesting modern physics papers and discuss them; no more, no less. A lot of it is way over my head as a chemist, but that's part of what makes me love it. The topics are always understandable, even if it takes self-study to get the nuances. One guy is a physicist and the other is a sculptor who, I assume, taught himself physics. Just a thing that would likely appeal to one who cares about particle physics and is not well satisfied by the preponderance of 'physics' podcasts that endlessly re-explain what entropy is or what wave/particle duality means. I wish more science podcasts dealt directly with modern research, and this one is a great example...even if they're skeptical about Copenhagen and prefer pilot-wave "realism". ° https://physicsfm-frontiers.blogspot.com https://physicsfm-frontiers.blogspot.com
- RosanaAnaDana 8y ago
  I'm very intersested in the idea of a podcast that does the same for topics in climate science, biology, natural sciences. Know of anything you could point me at?
  - nabla9 8y ago
    Sean Carroll's Mindscape Podcast is good general podcast from a physicist. https://www.preposterousuniverse.com/podcast/ https://www.preposterousuniverse.com/podcast/
  - est31 8y ago
    I've found talks on youtube to be very interesting. You can often just listen to them without watching the video. Some links: Allen institute lectures about neuroscience: https://www.youtube.com/watch?v=mtPgW1ebxmE&list=PLOpjORaUU74zmq6Pmo3O6dzhxFBtaGsdt https://www.youtube.com/watch?v=mtPgW1ebxmE&list=PLOpjORaUU7... A talk about the insight Mars lander by the guy who proposed the mission: https://www.youtube.com/watch?v=uXyLaER23aU https://www.youtube.com/watch?v=uXyLaER23aU Climate change (focused on Boston but he really knows his stuff): https://www.youtube.com/watch?v=MToNKd6RQhk https://www.youtube.com/watch?v=MToNKd6RQhk
leptoniscool 8y ago
Could this lead to a different approach to fusion?
- drpossum 8y ago
  No, this isn't directly related to fusion. The binding energies are already well known and nucleon modification effects in fusion are far to small to be meaningful.
cperciva 8y ago
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...
bawana 8y ago
where can i find simple explanation of how they distinguish elastic vs inelastic collisions? They talk about the ratio of elastic vs inelastic collisions as a function of incident particle energy which is where I am confused. Excuse my ignorance - I am interested though not schooled in the particulars of particle physics. They also talk about cross section - I imagine they calculate that based on the frequency of collisions - just like Rutherford did.
undersuit 8y ago
Could this pairing have something to do with radioactive decay? That neutrons and protons are interacting with themselves and each other, but that these interactions would have nothing to do with a unstable nucleus radiating a particle would make me slightly unhappy.

90 points by lainon 8y ago

The article on Semi-empirical mass formula [0] is also interesting read, especially deconstructing the formula and seeing what impact each term has (e.g. asymmetry term and the difference between the relation of number of protons to the number of neutrons). [0]: https://en.wikipedia.org/wiki/Semi-empirical_mass_formula https://en.wikipedia.org/wiki/Semi-empirical_mass_formula

Leace 8y ago
An interesting fact: free neutrons [0] are unstable and will decay into protons [1] with mean lifetime of ~15 minutes. That is one down quark will decay into an up quark (neutron is composed out of udd quarks, proton: uud) because down quarks have bigger mass than up quarks (see this nice Feynman diagram [2]). In the nucleus on the other hand Pauli exclusion principle makes two protons less favorable than a proton and neutron. Warning: this is what I understood from Wikipedia, IANAP (I am not a physicist). [0]: https://en.wikipedia.org/wiki/Neutron https://en.wikipedia.org/wiki/Neutron [1]: And a couple of other particles, see: https://en.wikipedia.org/wiki/Neutron#Description https://en.wikipedia.org/wiki/Neutron#Description [2]: https://commons.wikimedia.org/wiki/File:Beta_Negative_Decay.svg https://commons.wikimedia.org/wiki/File:Beta_Negative_Decay....

DiseasedBadger 8y ago

Does this draw into question whether there is such thing as a "nuclear field"?

teilo 8y ago
No. The "nuclear field" is just a term for the composite field resulting from the constituent particles of the nucleus (the quarks and gluons) and their interaction. For there to be no "nuclear field" there would have to be no nucleus. Well, that's not entirely correct, because particle fields permeate all of space. To grossly simplify, there's something happening in those fields in a nucleus. The various particle fields are vibrating and interacting. "Nuclear field" is just shorthand for this interaction that is the result of the presence of the particles of the nucleus. The result described in this article just rules out the nuclear field as being responsible for the EMC effect.
andrepd 8y ago
How do you mean?

criddell 8y ago

This is offtopic, but do neutrons and protons have a similar dual wave / particle nature like photons do? What about quarks and all the sub-particles?

dmitrygr 8y ago
Everything acts like a wave. The term to Google for is "de broglie wavelength". Even you have an effective wavelength and you refract (slightly) when passing through a slit (door)
- criddell 8y ago
  My brain just can't accept that. It's seems too nuts. What does mass mean when you are talking about waves and fields? What does it mean to collide two waves together and look for smaller waves coming out? Everything is divisible? Or is there some kind of Planck wavelength?
  - trentlott 8y ago
    You might be interested in Pilot Wave Theory. It tries to reconcile wave/particle duality by claiming there is a real physical particle at all times in an attempt to get around the strange idea of everything being a probablistic wavefunction (the Copenhagen interpretation). It explains some things pretty intuitively (double slit experiment), but from what I can tell it becomes too convoluted for other things. Mass can be related to energy with E=mc^2, and you can get some idea of its relation to wavelength and wave collisions. I think a smallest wavelength is unlikely, because it would put an upper bound on energy. The only side-effect of increasing the energy density (ie a lot of energy in a small space, like a very low-wavelength photon) is the formation of a black hole. I think the question of whether photons (massless) can form them is one of those quantum-gravity issues that are awaiting a theory.
    - perl4ever 8y ago
      "You might be interested in Pilot Wave Theory. It tries to reconcile wave/particle duality by claiming there is a real physical particle at all times in an attempt to get around the strange idea of everything being a probablistic wavefunction (the Copenhagen interpretation)." I don't understand much of anything, but based on what I read, I strongly prefer the idea that everything is a field and particles don't exist, rather than vice versa. It just feels right. We don't experience particles any more than waves in our daily lives anyway.

trentlott 8y ago

I want to take a second to rep my absolute favorite podcast, Physics Frontiers.° It's not a "pop-sci" podcast - they take a couple of interesting modern physics papers and discuss them; no more, no less. A lot of it is way over my head as a chemist, but that's part of what makes me love it. The topics are always understandable, even if it takes self-study to get the nuances. One guy is a physicist and the other is a sculptor who, I assume, taught himself physics. Just a thing that would likely appeal to one who cares about particle physics and is not well satisfied by the preponderance of 'physics' podcasts that endlessly re-explain what entropy is or what wave/particle duality means. I wish more science podcasts dealt directly with modern research, and this one is a great example...even if they're skeptical about Copenhagen and prefer pilot-wave "realism". ° https://physicsfm-frontiers.blogspot.com https://physicsfm-frontiers.blogspot.com

RosanaAnaDana 8y ago
I'm very intersested in the idea of a podcast that does the same for topics in climate science, biology, natural sciences. Know of anything you could point me at?
- nabla9 8y ago
  Sean Carroll's Mindscape Podcast is good general podcast from a physicist. https://www.preposterousuniverse.com/podcast/ https://www.preposterousuniverse.com/podcast/
- est31 8y ago
  I've found talks on youtube to be very interesting. You can often just listen to them without watching the video. Some links: Allen institute lectures about neuroscience: https://www.youtube.com/watch?v=mtPgW1ebxmE&list=PLOpjORaUU74zmq6Pmo3O6dzhxFBtaGsdt https://www.youtube.com/watch?v=mtPgW1ebxmE&list=PLOpjORaUU7... A talk about the insight Mars lander by the guy who proposed the mission: https://www.youtube.com/watch?v=uXyLaER23aU https://www.youtube.com/watch?v=uXyLaER23aU Climate change (focused on Boston but he really knows his stuff): https://www.youtube.com/watch?v=MToNKd6RQhk https://www.youtube.com/watch?v=MToNKd6RQhk

leptoniscool 8y ago

Could this lead to a different approach to fusion?

drpossum 8y ago
No, this isn't directly related to fusion. The binding energies are already well known and nucleon modification effects in fusion are far to small to be meaningful.

cperciva 8y ago

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...

bawana 8y ago

where can i find simple explanation of how they distinguish elastic vs inelastic collisions? They talk about the ratio of elastic vs inelastic collisions as a function of incident particle energy which is where I am confused. Excuse my ignorance - I am interested though not schooled in the particulars of particle physics. They also talk about cross section - I imagine they calculate that based on the frequency of collisions - just like Rutherford did.

undersuit 8y ago

Could this pairing have something to do with radioactive decay? That neutrons and protons are interacting with themselves and each other, but that these interactions would have nothing to do with a unstable nucleus radiating a particle would make me slightly unhappy.