The contenders have always been:Sir Ernest Rutherford, Ernest Walton, and John Douglas Cockroft.
Newly found academic papers and certain diary entries seem to indicate the fourth man, Percival H. Drypoofs, an itinerant rubber beater (?) and porchman (also ?) had managed the feat ten years prior to the other men and his method involved only a pool cue and a tooth.
His only known comment regarding the breakthrough was, "Yah, I gave it a right whack. 'Is loaf turned into a mushy cap, and me cheroot blew out!"