(i) In 1911, Geiger and Marsden did a remarkable experiment based on the advice of their teacher Rutherford, which is known as scattering of alpha particles by gold foil.
(ii) The experimental arrangement. A source of alpha particles (radioactive material, example polonium) is kept inside a thick lead box with a fine hole.
(iii) The alpha particles coming through the fine hole of lead box pass through another fine hole made on the lead screen. These particles are now allowed to fall on a thin gold foil and it is observed that the alpha particles passing through gold foil are scattered through different angles.
(iv) A movable screen (from `0^(@)` to `180^(@)`) which is made up of zinc sulphide (ZnS) is kept on the other side of the gold foil to collect the alpha particles. Whenever alpha particles strike the screen, a flash of light is observed which can be seen through a microscope.
(v) Rutherford proposed an atom model based on the results of alpha scattering. experiment.
(vi) In this experiment, alpha particles (positively charged particles) are allowed to fall on the atoms of a metallic gold foil. The result of this experiment. Rutherford expected the nuclear model, but the experiment showed the model.
(a) Most of the alpha particles are un-deflected through the gold foil and went straight.
(b) Some of the alpha particles are deflected through a small angle.
(c) A few alpha particles (one in thousand) are deflected through the angle more than `90^(@)`.
(d) Very few alpha particles returened back (back scattered) - that is, deflected back by `180^(@)`.
