
Why neutrons and protons are modified inside nuclei - lainon
https://www.nature.com/articles/d41586-019-00577-0
======
trentlott
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
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?

~~~
est31
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=PLOpjORaUU7...](https://www.youtube.com/watch?v=mtPgW1ebxmE&list=PLOpjORaUU74zmq6Pmo3O6dzhxFBtaGsdt)

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)

------
Leace
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
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....](https://commons.wikimedia.org/wiki/File:Beta_Negative_Decay.svg)

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cperciva
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?

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

~~~
cperciva
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?

~~~
raattgift
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.

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bawana
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.

------
leptoniscool
Could this lead to a different approach to fusion?

~~~
drpossum
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.

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undersuit
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.

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criddell
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?

~~~
nabla9
Yes. Also molecules and macroscopic objects.

The largest molecule where this has been experimentally verified had 810 atoms
(roughly 15,000 protons,neutrons and electrons).

Matter–wave interference of particles selected from a molecular library with
masses exceeding 10000 amu
[https://pubs.rsc.org/en/content/articlehtml/2013/cp/c3cp5150...](https://pubs.rsc.org/en/content/articlehtml/2013/cp/c3cp51500a)

~~~
hi41
Thank you. I too had the same question. At what size does this wave particle
feature stop? For example a coffee cup does not toggle between being a wave
and a particle.

~~~
Florin_Andrei
> _a coffee cup does not toggle between being a wave and a particle_

Neither does an electron, for that matter.

Particles such as electrons, protons, etc, are quantum objects. They're not
waves. They're not particles. They are quantum objects - which means they have
some wave-like properties, and some particle-like properties, but really are
something else altogether.

~~~
rrmm
The toggling that does occur is in our mathematical treatment of the objects:
sometimes it is advantageous to model them as a billiard ball and other times
as a disturbance of a field. Sometimes you have no choice but to treat them
fully as the quantum object they are.

It just depends on whether you can eliminate some part of the complexity and
still come up with an answer that is useful in reality.

~~~
criddell
This is something I've wondered about. Is the particle and wave idea just a
calculation model or does that seem to be how things are actually constructed?

For example, the Bohr model of the atom probably doesn't reflect how atoms are
but 100 years ago (and in high school today) it's a useful model.

~~~
Florin_Andrei
Both "particle" and "wave" are simplifications. And yes, models can be useful.

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

~~~
teilo
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.

