Question

How alpha particles beamed through gold foil

Answer 1

there is space between the atoms of gold and it is through this space that alpha beam went through. The ones who hitted got deflected

Answer 2

Rutherford experimented this experiment.
The thin gold foil was bombarded with alpha particles. On bombarding the alpha particles scattered in different directions (in different angles).
 
They were detected by florescent detector(which rotated) and has a microscope and a screen coated with zinc sulphide.