Rutherford’s Scattering Experiment

The Experiment:

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Image from: Kurzon - CC BY-SA 3.0 1

Alpha particles (particles with 2 protons and 2 neutrons, hence positively charged) are fired at very thin gold leaf. The angle of deflection is measured using a fluorescent screen encapsulating the radium source which lights up when impacted by an alpha particle. A microscope is used to view the paths of alpha particles.

Conclusions:

  1. The atom must be mostly empty space - This is because the majority of the alpha particles pass through the gold leaf unaffected.
  2. The nucleus must contain the majority of the mass of the atom - This is because for an alpha particles to be deflected in the way that was observed they must be impacting something more massive than themselves.
  3. The nucleus must have a large positive charge - This is because the positively charged alpha particles, when deflected, often are deflected by a very large angle.
  4. The nucleus must be very small - This is because very few of the alpha particles are deflected more than $90^{\circ}$.

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Image cropped from: Kurzon - CC BY-SA 3.0 2

  1. https://commons.wikimedia.org/wiki/File:Geiger-Marsden_experiment_results.svg, https://creativecommons.org/licenses/by-sa/3.0/deed.en ↩︎

  2. https://commons.wikimedia.org/wiki/File:Geiger-Marsden_experiment_expectation_and_result.svg, https://creativecommons.org/licenses/by-sa/3.0/deed.en ↩︎