Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
Ernest Rutherford (1871-1937) worked with radioactivity, which he found to be of different kinds, distinguishing between positive, or alpha rays, and negative, or beta rays. He discovered that the alpha particles were helium nuclei, which he used to bombard very thin metal foils. Sometimes the alpha particles were scattered backward as if repelled by other positive charges; this led Rutherford to propose the theory of a nuclear atom, containing a very small positive nucleus, surrounded by negatively charged electrons and a great deal of empty space.