page_title: Geiger–Marsden experiment
section_title: The outcome of the experiments
hierarchical_section_title: Geiger–Marsden experiment / Summary / The outcome of the experiments
context_page_description: The Geiger–Marsden experiments were a landmark series of experiments by which scientists discovered that every atom has a nucleus where all of its positive charge and most of its mass is concentrated. They deduced this after measuring how an alpha particle beam is scattered when it strikes a thin metal foil. The experiments were performed between 1908 and 1913 by Hans Geiger and Ernest Marsden under the direction of Ernest Rutherford at the Physical Laboratories of the University of Manchester.
context_section_description: At Rutherford's behest, Geiger and Marsden performed a series of experiments where they pointed a beam of alpha particles at a thin foil of metal and measured the scattering pattern by using a fluorescent screen. They spotted alpha particles bouncing off the metal foil in all directions, some right back at the source. This should have been impossible according to Thomson's model; the alpha particles should have all gone straight through. Obviously, those particles had encountered an electrostatic force far greater than Thomson's model suggested they would. Furthermore, only a small fraction of the alpha particles were deflected by more than 90°. Most flew straight through the foil with negligible deflection.
  To explain this bizarre result, Rutherford imagined that the positive charge of the atom was concentrated in a tiny nucleus at its center, which in turn meant that most of the atom's volume was empty space.
caption: Left: Had Thomson's model been correct, all the alpha particles should have passed through the foil with minimal scattering.
   Right: What Geiger and Marsden observed was that a small fraction of the alpha particles experienced strong deflection.