Positively charged particles emitted from a radioactive source (radium).
At the time, scientists believed in the , where an atom was a blob of positive charge with electrons scattered inside like fruit in a pudding. If this were true, the heavy alpha particles should have whizzed straight through the "soft" atoms. Rutherford Gold Foil Experiment - Backstage Science
While most did pass through, Rutherford was shocked to find that: scientists believed in the
To look inside the atom, Rutherford needed to fire something at it. He used: 000 atoms thick.
Chosen because gold is incredibly malleable and can be beaten into a sheet only about 1,000 atoms thick.