Rutherford's initial research was studying alpha particles, which he hypothesized were helium nuclei. With the help of Hans Geiger, Rutherford conducted the gold foil experiment, which justifies that the nucleus of an atom is a dense collection of protons and contains the majority of an atom’s mass. It also inferred that most of the atom is empty space and electrons are not located in the nucleus. He won the Nobel Prize in chemistry in 1908 for his studies on radioactive substances.