Whose experiment first proved that atoms can be split into subatomic particles by studying alpha particles?

Ernest Rutherford and his collaborators Hans Geiger and Ernest Marsden fired alpha particles at thin gold foil. Most particles passed through, but a few bounced back at surprising angles. Rutherford concluded that atoms are mostly empty space with a tiny, dense, positively charged nucleus at the center. This overturned the older plum pudding model of the atom. The experiment became a cornerstone of modern atomic physics and chemistry.