Nuclear experiments began using a particle accelerator built by John Cockcroft and Ernest Walton at Ernest Rutherford 's Cavendish Laboratory at the University of Cambridge. In 1932, Walton produced the first man-made fission by using protons from the accelerator to split lithium into alpha particles. The accelerator was then used to fire deuterons at various targets. Working with Rutherford and others, Mark Oliphant discovered the nuclei of helium-3 (helions) and tritium (tritons), the first case of human-caused fusion.