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Question: Does the nuetron have a tiny electric charge?

  1. Jul 7, 2009 #1
    I was going through wikipedia and other online 'resource' sites trying to to find an answer to this question, and the answers I came across were difficult for me to interpret. Obviously in general terms the Neutron has a charge of 0 but I remember once reading a few years ago that it might have a tiny electric charge. If it does, what's the sign of the charge and how tiny is its magnitude?

    Thanks.
     
  2. jcsd
  3. Jul 7, 2009 #2

    Vanadium 50

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    The neutron has, to a high degree of precision, no charge.
     
  4. Jul 10, 2009 #3

    jtbell

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    What you saw was probably a reference to an experimental upper limit on the charge of the neutron. No experimental measurement is exact, there is always some uncertainty associated with it. Reporting an upper limit basically says, "we didn't detect anything, so if the neutron has a net charge, it must be less than this amount which reflects our experimental uncertainty." The word "if" is crucial here.
     
  5. Jul 10, 2009 #4

    turin

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    Or, perhaps you saw electric dipole but are remembering it as electric charge. There are four electromagnetic form factors, and three of them can be nonzero for neutral composite particles. (Don't confuse form factors with moments. While similar, the concept is distinct.) The electromagnetic form factors can be orgainzed as: electric charge, magnetic moment, electric (dipole) moment, and anapole (moment). In my opinion, the anapole is particularly strange, as it is only manifested by direct contact with electromagnetic matter current. I think that the only nonzero form factor that is possible for a fundamentally neutral particle (that is, a neutral point particle) is the anapole.
     
  6. Jul 10, 2009 #5
    The upper limit for the neutron charge in my 2002 Particle Data Group book is less than 10-21 times the electron charge. The value for the electric dipole moment of the neutron in my 2002 Particle Data Book is less than 0.63 x 10-25 e-cm. This does not mean that the neutron has an electric dipole moment, but this is the uncertainty in the measurement. This means that if there were two opposite charges, a +q and a -q, separated by 10-13 cm (typical nuclear size), the +q and -q would be less than about 10-12 times the electron charge.
    [Edit} See page 6 of
    http://pdg.lbl.gov/2009/listings/rpp2009-list-n.pdf
    for neutron charge measurement
     
    Last edited: Jul 10, 2009
  7. Jul 13, 2009 #6
    The neutron has no *net* charge. But it is comprised of 3 basic particles called quarks, which do have charge. A neutron is 1 up quark plus 2 down quarks. The up quark has a charge of +2/3, vs. the down quark whose charge is -1/3. The sum is zero.

    A proton OTOH, is 2 ups & 1 down, for a net charge of +1.

    Does this help?

    Claude
     
  8. Jul 13, 2009 #7
    It has no dipole moment, within the limits of measurements. If there were two electron-size opposite charges or quarks with different charges, they would have to be less than about 10-25 cm apart. The neutron size is about 10-13 cm.
     
    Last edited: Jul 13, 2009
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