Ernest Rutherford and the Atom article

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Imagining Science

Ernest Rutherford – The nuclear atom

Today we’re going to be looking at Rutherford’s alpha-particle scattering experiment and how, through this, he found ground-breaking new evidence on the structure of a nuclear atom.

Ernest Rutherford, a notable English physicist, in the 20th century understood that all matter is made up of atoms. However, he wanted to delve deeper in this understanding about atoms. As a result in 1909, along with his assistants, Hans Geiger and Ernest Marsden, carried out an experiment  to investigate a detailed model for the atom (the ‘inner-workings’).

Diagram of Rutherford’s Alpha-Particle Scattering Experiment

What Rutherford did was quite unique. He used and a He used a source which emitted alpha particles (charged helium ions), and directed the beam of alpha particles towards a thin gold foil (he wanted a thin layer as thin a layer as possible) to observe any effects between the two.

Rutherford’s Observations

  • Roughly 99% of the alpha particles passed straight through the foil.
  • Some of the alpha particles were deflected by the foil at small angles - 1 in 8000 alpha particles were deflected at around 90° and over.  
  • Around one out of every 12000 particles to rebounded off the gold foil – some directly in the opposite direction!
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Rutherford stated that:

“It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”

Rutherford’s Explanation about the Observations

Rutherford inferred from the observations that there must be a positive charge in the atom due to the fact that the alpha particles, which were repelled, were positively-charged (as similar charges repel each other and cause them to scatter in ...

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