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Author Topic: How do Protons and Neutrons Generate and Respond to the Strong Nuclear Force?  (Read 4316 times)

Offline evan_au

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Two parallel discussions on "Is proton-proton fusion feasible?" and "What is the evidence for the existence of protons and neutrons?" raised a possibility that I had not considered previously...
  • It seems that protons feel the strong nuclear force, but also generate it. They also feel the electrostatic force, so two protons (a diproton) mostly disintegrates back into two protons (but sometimes into deuterium).
  • It seems that neutrons are attracted by the strong nuclear force, but do not generate it? So two neutrons (a dineutron) are not bound together by the strong nuclear force, and they just drift apart?
  • So to produce a stable nucleus heavier than a proton, you need both protons & neutrons.
     
A rather weak analogy using magnetism might look something like this:
  • "Soft" iron does not generate an external magnetic field, but it does respond to a magnetic field, and will be attracted into an external magnetic field
  • A permanent magnet generates an external magnetic field, and will respond to an external magnetic field. 

Can someone explain this apparent asymmetry between protons & neutrons in their generation & response to the strong nuclear force, in more technical terms? Thanks...
« Last Edit: 04/09/2015 01:53:34 by chris »


 

Offline PmbPhy

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Quote from: evan_au
  • It seems that neutrons are attracted by the strong nuclear force, but do not generate it? So two neutrons (a dineutron) are not bound together by the strong nuclear force, and they just drift apart?
Why do you say this? A neutron is a hadron just as a proton is. By definition, the strong force is that interaction which holds hadrons together. So I can't see why you'd say that a proton feels the strong force and generates it while the neutron only is attracted by it. There's no difference between the proton and neutron as far as the strong force goes. As far is it goes they're both hadrons.
 

Offline mathew_orman

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Strong force fails stability making all nucleus attract and combine just like gravity... Or is there another type of force preventing self attraction?

 
 

Offline evan_au

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Quote from: PmbPhy
I can't see why you'd say that ...the neutron only is attracted by [the strong nuclear force].

This comment was triggered by the following description of a dineutron:
Quote from: Wikipedia
A system made up of only two neutrons is not bound, though the attraction between them is very nearly enough to make them so.

The reference includes the comment:
Quote
The stability of the deuteron is a result of the nuclear force being stronger when the nucleons have parallel spin than when the spins are opposite. The Pauli exclusion  principle requires that the nucleons in the diproton and dineutron have opposite spin."

...a 9% increase in the strong force coupling constant, αs, is sufficient to bind the dineutron and a 13% increase will bind the diproton. The needed increase in coupling constant to bind the diproton was ...due to the electrostatic repulsion of the protons

This paper suggests that the strong force between neutrons is similar in strength to the strong force between protons.

So I conclude, after further investigation that both neutrons & protons will generate & feel the strong nuclear force.
 

Offline PmbPhy

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Quote from: mathew_orman
Strong force fails stability making all nucleus attract and combine just like gravity.
What does that mean? Please justify this assertion as well.
 

Offline jeffreyH

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Free neutrons are in a state of decay. The fact that they last around 15 mins means that the potential for decay is lower than for shorter-lived particles but still high. Can a particle heading towards decay ever reach a bound state unless its partner adds a charge to the combined system? This may be why two neutral neutrons won't bind.
 

Offline Atomic-S

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According to the earlier-cited source, two neutrons won't bind because they cannot assume the necessary parallel spins required for an adequate strong force. As for the role of charge in preventing neutron decay or for any other purpose -- this is a difficult subject requiring significant knowledge of quantum structure as it pertains to mesons (which are involved in this process), quarks, and gluons. I am no an expert, but in rough terms, I understand that the gluons hold the quarks together, this arrangement making protons, neutrons, and mesons; and the mesons end up holding the protons and neutrons together.
 

Offline mathew_orman

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If role of neutron is to generated force field which should hold all the repelling protons together then i must also have force which holds all neutrons together but then all nucleus would attract them-selfs creating infinitely large nucleus of equally infinite size...
Current nuclear model of an atom does not make any sense..
 

Offline evan_au

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Quote from: mathew_orman
all nucleus would attract them-selfs creating infinitely large nucleus
The strong force has an extremely short range.
The minimum average orbital radius of an electron is larger than the range of the strong nuclear force.

So at room temperature, the electrons around the nucleus act as a barrier to nearby nuclei fusing together.

Even if you heat atoms until they become a plasma and all the electrons are stripped off, the nucleus still has a strong electrostatic field, which has a greater range than the strong nuclear force. So this, too, acts as a barrier to nuclei fusing together.

Quote
"infinitely" large nucleus
Something like this can occur in a neutron star, left behind in the ashes of a supernova explosion.

A neutron star has the protons and neutrons packed together with the density of a uranium nucleus. It can have 1-2 times the mass of the Sun, which makes it a pretty big nucleus, compared to (say) uranium.
 

Offline mathew_orman

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I looks like more research need to be done...
The only reliable knowledge states that electrons and atoms exist...
Other subatomic particle are just hypothetical...

Thank you for your help...
 

Offline evan_au

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Quote from: mathew_orman
The only reliable knowledge states that electrons and atoms exist...Other subatomic particle are just hypothetical
Have a look at this animation of the Large Hadron Collider:
  • The two particles that you follow for the first part of the video are protons (ie neither electrons or atoms).
  • The enormous complexity of the instrumentation where the protons collide is so that the scientists can track the position, charge, mass, velocity, energy and lifetime of the particles in the debris field. And much of the debris is not electrons nor atoms.
  • So these other particles are not just hypothetical. 
 

Offline mathew_orman

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It is not clear how they produce a proton to start with. Thus the rest is built on assumptions...
 

Offline evan_au

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Quote from: mathew_orman
It is not clear how [the LHC] produce a proton to start with
They have a small tank of hydrogen gas, and pass the hydrogen through an electric arc to rip off the electrons, leaving a pair of protons, which get fed into the first stage of the LHC.

So protons are just as fundamental as atoms and electrons, in that: Hydrogen atom = electron + proton

....and Neutrons are almost as fundamental, because about 1 in 10,000 Hydrogen atoms has double the mass: when you put it in an electric arc, you have a proton and a neutron bound together, which behaves distinctly differently than a proton alone.
 

Offline mathew_orman

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That does not prove that the outcome is proton which was invented in first place and not discovered yet...
Nothing but a pyramid of hypotheses...
 

Offline acsinuk

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    • electricmagnofluxuniverse.blogspot.com
So is the deuterium molecule containing 2 protons or 1 proton and 1 neutron? and what about tritium?
 

Online chiralSPO

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A deuterium atom contains 1 proton and 1 neutron and 1 electron. A deuterium molecule contains 2 protons and 2 neutrons as 2 nuclei, bound together by 2 electrons...
 

Online chiralSPO

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That does not prove that the outcome is proton which was invented in first place and not discovered yet...
Nothing but a pyramid of hypotheses...

I have a hypothesis: mathew_orman doesn't exist.

Prove me wrong! Sure, I see evidence of his existence, but it could all be explained by ever more complex theories...
 

Offline evan_au

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Quote from: acsinuk
the deuterium molecule...
About 1 in 10,000 hydrogen atoms is Deuterium. A vanishingly small fraction are Tritium - it decays in about 11 years, and has to be manufactured in nuclear plants.

The most likely place to find Deuterium is in seawater, where about 1 in 10,000 water molecules will weigh about 6% more than the than the usual water molecule, due one extra neutron (one deuteron).

If you made hydrogen gas from seawater, there would be around 0.01% of hydrogen molecules containing 1 Deuterium atom and 1 "Normal" hydrogen atom. There would be a microscopic fraction (around 0.00001%) that consisted of 2 deuterium atoms.

It is certainly possible to extract the deuterium, and make water with 100% deuterium ("Heavy Water" for some nuclear reactors), and even 100% Deuterium gas.

It is even possible to make proteins with deuterium (or tritium), and follow the biochemical pathways that metabolize these chemicals into their final products.
« Last Edit: 10/09/2015 13:51:18 by evan_au »
 

Offline evan_au

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Quote from: mathew_orman
That does not prove that the outcome is a proton which was invented in first place and not discovered yet
CERN uses about 200MW of electricity, enough for a fair sized city. Much of that is used to power the magnets and electronics which accelerate bunches of these "hypothetical" protons.

They have instruments that count how many protons are in each bunch - a current flow of protons is just as real as the current flow of electrons in your light globe.

If there is a malfunction, they must quickly dump the energy in these proton beams (within microseconds) - an energy equivalent to 173kg of TNT. This is very real energy, stored in very real particles!
 

Offline mathew_orman

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The CERN is not a prove of existence of neutrons or protons...
 

Offline PmbPhy

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Quote from: mathew_orman
The CERN is not a prove of existence of neutrons or protons...
Science is not about proving anything. That's a common misconception about science. If you're new to this fact then watch this video which is on my companies website: http://www.newenglandphysics.org/common_misconceptions/DSC_0002.MOV

The operation of the CERN collider is consistent with the existence of protons and neutrons. That's what scientific evidence means, i.e. that you have information which is consistent with an hypothesis or theory being correct.

I have a book called Great Experiments in Physics which describes Chadwick's discovery of the neutron. I'll scan it in and post it later today.

Meanwhile there are the following pages which describe the discovery of the proton and neutron, respectively:
http://chemed.chem.purdue.edu/genchem/history/proton.html
http://ansnuclearcafe.org/2011/10/19/pioneers102011/
« Last Edit: 11/09/2015 16:21:46 by PmbPhy »
 

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