<P> At Rutherford's behest, Geiger and Marsden performed a series of experiments where they pointed a beam of alpha particles at a thin foil of metal and measured the scattering pattern by using a fluorescent screen . They spotted alpha particles bouncing off the metal foil in all directions, some right back at the source . This should have been impossible according to Thomson's model; the alpha particles should have all gone straight through . Obviously, those particles had encountered an electrostatic force far greater than Thomson's model suggested they would, which in turn implied that the atom's positive charge was concentrated in a much tinier volume than Thomson imagined . </P> <P> When Geiger and Marsden shot alpha particles at their metal foils, they noticed only a tiny fraction of the alpha particles were deflected by more than 90 ° . Most just flew straight through the foil . This suggested that those tiny spheres of intense positive charge were separated by vast gulfs of empty space . Most particles passed through the empty space and experienced negligible deviation, while a handful struck the nuclei of the atoms and bounced right back . </P> <P> Rutherford thus rejected Thomson's model of the atom, and instead proposed a model where the atom consisted of mostly empty space, with all its positive charge concentrated in its center in a very tiny volume, surrounded by a cloud of electrons . </P> <P> Ernest Rutherford was a physics professor at the University of Manchester . He had already received numerous honors for his studies of radiation . He had discovered the existence of alpha rays, beta rays, and gamma rays, and had proved that these were the consequence of the disintegration of atoms . In 1906, he received a visit from a German physicist named Hans Geiger, and was so impressed that he asked Geiger to stay and help him with his research . Ernest Marsden was a physics undergraduate student studying under Geiger . </P>

Who discovered that most of an atom is empty space