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Size of electron

  1. Jan 17, 2009 #1
    everyone knows that Rutherford fired alpha particles at high speed at gold foil and some rebounded directly back and that from this he concluded that it must be very small. what about electrons. if electrons are fired at high speed at gold foil then do some rebound directly back? how far down does this sort of experiment show the field of the electron extending to.

    how much energy can electrons have and still rebound directly backwards?
  2. jcsd
  3. Jan 17, 2009 #2


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    I don't know about gold foil, but there has been at least one high-energy accelerator used for electron-proton collisions: HERA at DESY in Hamburg, Germany.
  4. Jan 17, 2009 #3
    It should be emphasized that Rutherford discovery is not merely about some backwards scattering. It's about the angular distribution of the scattering. In fact, most of the alphas were almost not deflected, indicating that the gold nucleus was smaller than Thomson's "plum pudding".
  5. Jan 17, 2009 #4


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    Firing electrons at gold or at protons does not measure the electron size, because the gold and the proton are too big themselves. Electron electron scattering is consistent with scattering of point charges. The accuracy of the experiments provides a very small upper limit to the electron radius.
  6. Jan 17, 2009 #5
    The tightest upper bound on the electron radius that I'm aware of is [tex]r < 10^{-22}[/tex] meters, from this paper. High-energy scattering experiments can probe down to [tex]r \sim 10^{-20}[/tex] meters, if I recall correctly, at which distance the electron still "looks pointlike".
  7. Jan 18, 2009 #6


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    Hans Dehmelt won the Nobel prize for experiments like that. His result is a smaller upper limit than e-e scatering. All measurements are consistent with a point-like electron, which is the preferred theoretical model.
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