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Size of a neutron

  1. Apr 13, 2008 #1
    If a proton and neutron have a mass of roughly 1.67e-27 kg . And a proton has a diameter of 1.65e-15 ..
    Is the diameter of a neutron the same?
  2. jcsd
  3. Apr 13, 2008 #2


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  4. Apr 13, 2008 #3


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    For all intents and purposes they are about the same. But concepts like diameter or radius in the context of small spheres, like ball-bearing in our everyday experience, are meaningless when applied to subatomic particles.
  5. Apr 13, 2008 #4

    Astronuc, The "diameter" is more of a orbital boundary, correct?
  6. Apr 13, 2008 #5
    It will be hard and long to make sens of such a concept in the case hadrons. It is doable, it has been done, but there is virtually no experiment shedding light on this specific approach to hadron structure.

    The problem if you talk about "orbit" is that you have to take both position and momentum in the game. With ultra-relativistic light quarks confined in a proton/neutron, there is a long and technical path before you reach any kind of reward. What has been done for long and measured is effective electromagnetic radius for instance. You can interpret that as a position charge distribution density, without reference to momentum.
  7. Apr 15, 2008 #6
    If the diameter is the same, then the density must be roughtly the same as well. The difference between composition of neutron and proton is that neutron is made up of 2 down quarks and 1 up quark while proton is made up of 2 up quarks and 1 down quark. I am not sure of the density of the up and down quarks but if they are roughly similiar they the conclusion that the diameter of neutron thus its density is roughly similiar to that of a proton is true.
  8. Apr 26, 2008 #7
    Usually the linear size of charged particle is Compton wavelength (1.65e-15 m is c.w. of a proton)
    [tex]\lambda_C = \frac{\hbar c}{m c^{ 2 }}[/tex]

    Therefore if neutron had been charged its size would has been equal to proton size, proton and neutron have about same [tex]\lambda_C[/tex] as [tex]m_{p} \approx m_n[/tex]. Your question is not trivial because size of a particle is defined trough forces of its interactions.
  9. Apr 26, 2008 #8
    I am not too sure about those agruments. What is the Compton wavelength of a u or d quark ? How does it compare with the size of a nucleon ? What can we conclude about the semi-classical approximation of a static-potential like confinement scenario, such as t'Hooft's dual-color-superconducting model of the vacuum ? Can we re-interpret this model in terms phase transitions a la Gribov ?
  10. Apr 27, 2008 #9
    It's good example, quarks are very strongly interacting particles, their sizes are not defined trough their Compton wavelengths.
    This model and tricks are not well-known for me, may you advise to me some good books and/or articles about it with rapidly clear explanation?
  11. Apr 27, 2008 #10
  12. Apr 28, 2008 #11
    Thanks, I'll taste it.
  13. Apr 28, 2008 #12
    I was surprised to find a neutron weighed more than a proton as I always thought a protron
    as a neutron with a positive electron inside it (or something like that).
    But then maybe a neuton is is a proton with an electron inside it?
    Actually if you look at the atomic weights a neutron is probably a proton with three electrons stuffed inside it.
    Has this been confirmed by atom bashing????
  14. Apr 28, 2008 #13


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    no it weight more due to its different quark composition.

    And atomic weight of a neutron? Huh?
  15. Apr 29, 2008 #14
    Something like this is what appears on: http://www.terra.es/personal/gsardin/news13.htm
    There is a lot that can be done with this and values that have been discarded such as the Classical Radius; but the difficulty is that there are no forums where incomplete theories (i.e. theories under development) are taken seriously and it is of course, inappropriate to mention them on other forums.
    'Atom bashing' experiments use a selective computer program with the result that only two or three results, out of each batch of 80,000 results; are selected for investigation. This has lead to the PDG pointing out that experimental results are theme related.
    The whole question of particle structure is unresolved.
  16. Apr 29, 2008 #15
    Maybe you can explain us what you know about particle physics ?

    In most of those laboratories, and universities as well, one can count several hundreds, even thousands, of people whose daily purpose is to unravel those structures. They are working hard, and have been studying for a long time. You might be very surprised, if you took time to pay them a visit, to realise that they are not that close minded at all. On the contrary. But also, you might be surprised if you would take the time to seriously try to understand what they do, to realise that they are making continuous progress on our understanding. You will not find their latest understanding in the textbooks, because it is still considered speculative. You do need however to go through the textbooks in order to read the published articles, which is where you will find reports on what they are currently doing.

    I emphasized published because you are more than welcome to publish you own theory so that we discuss it here.
    Last edited: Apr 29, 2008
  17. Apr 30, 2008 #16

    You might be very surprised, if you took time to pay them a visit, to realise that they are not that close minded at all.

    I have never said they were. The crux of my case lies in the second part of your reply:

    You will not find their latest understanding in the textbooks, because it is still considered speculative.

    My work has been dismissed as ‘speculation’ so where does one go to debate speculative theories. Professionals, as you point out; have there associates in laboratories and universities but, the only hope for the complete amateur is the internet; but then comes the catch, only published works are eligible for debate on any forum worth calling a Science Forum.
    All my work is done by re-arranging PDG listings, Tables of Elements and tables published in papers on Hall fractions; to show mathematical relationships that have (as far as I am aware) not been published. So I am looking for a forum on speculations, where the moderators decide what is worthy of serious debate and reject the pseudo-science; if my work were then rejected (with reason) then although disappointed, I would at least, know where I stand. But to be rejected as speculation, without reason, leaves me uncertain as to whether I should continue or give up.
    (Debate precedes progress.)
  18. Apr 30, 2008 #17


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    Humanino: "I emphasized published because you are more than welcome to publish you own theory so that we discuss it here."

    I dont know where the boarder lies between "own theories" and "own/speculative theories" that is mentioned in the forum rules.
  19. Apr 30, 2008 #18
    Sorry, I was not clear.

    People are welcome to publish their theories in peer reviewed papers (read : somewhere else) so that we can discuss them here. :smile:
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