 In 1899, Ernest Rutherford showed the difference between alpha and beta radiation. He found that alpha radiation stopped in paper, but beta radiation was a hundred times more penetrating. In the next year in 1900, Vallard discovered the next type of radiation, gamma radiation. He used a piece of equipment that looked something like this. The radiation that's emitted from the source goes through the collimator. The alpha radiation was stopped in the lead foil, and the other radiation could penetrate through and pass through the magnetic field. He found that there were two different types of radiation coming out of the lead foil. One of them was bent in the magnetic field, and another one went straight ahead. The end result was he separated the three different types of radiation. The alphas were stopped in the lead foil, the betas were bent in the magnetic field, and the new type of radiation, the gammas, went straight ahead and weren't affected by the magnetic field. Now that three different types of radiation had been identified, the race was on to try and prove what these different types of radiation were. In 1900, Beckville measured the mass to charge ratio for beta particles and showed that it was exactly the same as an electron, and hence it was decided that beta particles must be electrons. In 1907, Rutherford and Boyds proved that alpha particles were positively charged helium atoms. Finally, in 1914, Rutherford and Andrade managed to reflect gamma rays off a crystal surface, and this demonstrated that they were actually electromagnetic radiation. After Rutherford had managed to identify that alpha particles were actually helium atoms, he became interested in trying to understand why they didn't travel very far in material and whether it was possible to scatter them off different types of material. He worked with his colleague Geiger and an undergraduate student Marsden, and over 1908 to 1913 he set up an experiment where he scattered alpha particles off a gold foil.