Gold foil Experiment and conclusions:
Helium Ions (α-particles) from a radioactive material (Radium) is passed through narrow slits to collimate them into straight-line path. Fast moving α-particles are made to hit a thin sheet (foil) of gold metal of about 100nm thickness. A photographic film or a screen coated with fluorescent- zinc sulphide material, is kept around the gold foil. Number and the angle of deflection of the scattered α-particles all around the gold foil, is measured by their interaction, with the film.
From the location and number of α-particles reaching the screen, Rutherford concluded the following:
i) Almost 99% of the α-particles pass through the gold foil without any deflection.
So atom must be having a lot of empty space in it.
ii) Several α-particles get deflected at angles.
α-particles being positive, the deflection can be caused only by the presence of another positively charged particle inside the atom.
iii) A few α-particles (one in twenty thousand) do not either go through or get deflected by the atom, rather they bounces back.
A heavy and highly positively charged particle must then have opposed these, few α- particles
in the atom. A higher charge density indicate a smaller size. Rutherford considered this smaller sized positive charged part as a dense core and called it as nucleus. Nucleus contains all the protons present in the atom and hence the mass of the atom.