Whose experiment first split the atom?

In 1932 John Cockcroft and Ernest Walton, working in Rutherford laboratory at Cambridge, used a machine that accelerated protons to smash into lithium atoms, breaking their nuclei apart into helium nuclei. This was the first time an atomic nucleus had been deliberately split, or disintegrated, using artificially accelerated particles. Earlier, Rutherford himself had induced a nuclear reaction in 1917 using natural particles. The 1932 experiment confirmed Einstein famous relationship between mass and energy in a nuclear reaction. Cockcroft and Walton shared the Nobel Prize in Physics in 1951 for this pioneering work.