What Happens When High-Speed Electrons Hit Gold Foil?

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Discussion Overview

The discussion centers on the behavior of high-speed electrons when they collide with gold foil, drawing parallels to Rutherford's experiments with alpha particles. Participants explore the implications of such collisions for understanding the size and properties of electrons, as well as the energy levels at which electrons might rebound from targets like gold or protons.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether high-speed electrons, similar to alpha particles, would rebound directly back when fired at gold foil and seeks to understand the extent of the electron's field in such experiments.
  • Another participant mentions the HERA accelerator, which has been used for electron-proton collisions, suggesting that there are existing experiments involving high-energy electrons.
  • A participant emphasizes that Rutherford's findings are not solely based on backward scattering but also on the angular distribution of scattering, indicating the size of the gold nucleus relative to earlier models.
  • It is noted that firing electrons at gold or protons does not measure the electron's size due to the larger size of the targets, and that electron-electron scattering supports the idea of electrons as point charges.
  • One participant cites a specific upper limit on the electron radius, referencing a source that discusses high-energy scattering experiments and their implications for the electron's point-like nature.
  • Another participant mentions Hans Dehmelt's Nobel Prize-winning work, which provides a smaller upper limit for the electron radius and supports the point-like model of electrons.

Areas of Agreement / Disagreement

Participants express differing views on the implications of electron scattering experiments, particularly regarding the measurement of electron size and the relevance of various scattering experiments. No consensus is reached on the specific outcomes of firing electrons at gold foil.

Contextual Notes

Participants acknowledge limitations in measuring the electron size due to the relative sizes of the targets used in experiments. The discussion includes references to specific upper limits on the electron radius and the conditions under which electrons are considered point-like.

Who May Find This Useful

This discussion may be of interest to those studying particle physics, experimental methods in high-energy physics, or the properties of fundamental particles like electrons.

granpa
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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?
 
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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.
 
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".
 
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.
 
The tightest upper bound on the electron radius that I'm aware of is r < 10^{-22} meters, from http://www.iop.org/EJ/abstract/1402-4896/1988/T22/016/. High-energy scattering experiments can probe down to r \sim 10^{-20} meters, if I recall correctly, at which distance the electron still "looks pointlike".
 
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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