How did Hans Geiger discover the atomic nucleus?

In the Geiger-Marsden gold foil experiment, a stream of alpha particles were fired at a sheet of gold foil, one atom thick. This setup was surrounded by a zinc sulphide screen which would scintillate if hit by an alpha particle.

At the time, the prevelant model of the atom was known as the 'plum pudding' model, which suggested that an atom was a sphere of uniform density with electrons randomly distributed within, like the raisins in a plum pudding. With this model the alpha particles should only have been deflected by a small amount at most.

When the experiment was carried out, most alpha particles streamed straight through the foil, as expected (the gaps between gold atoms were quite large and so alpha particles could fit through easily). Some were deflected through small angles and an even smaller number were deflected through angles of greater than 90 degrees. This was totally unexpected.

Ernest Rutherford did some calculations and worked out that the only way this could happen was if a large amount of the mass and charge of the atom was concentrated very highly in the centre of the atom (a nucleus) and surrounded by a lot of empty space and a few electrons.