The person generally credited with discovering the atomic nucleus is the New Zealand-born British physicist Ernest Rutherford. In an experiment conducted in 1911, Rutherford's team directed a beam of alpha particles (helium nuclei) at a thin sheet of gold foil. Most of the alpha particles passed through the foil without any deflection, indicating that most of the atom is empty space. However, a small number of alpha particles were deflected at large angles, suggesting that there was a small, dense core at the center of the atom. Rutherford calculated that this core, which he called the "nucleus," contained most of the atom's mass and positive charge.