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Draw a schematic arrangement of the Geiger-Marsden experiment. How did the scattering of a-particles by a thin foil of gold provide an important way to determine an upper limit on the size of the nucleus ? Explain briefly. |
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Answer» Solution :A schematic arrangement of the Geiger-Marsden experiment is shown in Fig. 12.11. In their experiment it was observed that most of the alpha-particles pass through the gold foil without any APPRECIABLE deflection. Some a particles are scattered through different angles and a very small number of particles suffers large angle scattering of about `180^(@)` Large angle scattering can be explained if we consider the ENTIRE positive charge and almostwhole mass of gold foil atom to be concentrated in a tiny central core of the atom. When an `alpha`-particle with kinetic energy K approaches the gold nucleus DIRECTLY along itscentral line it SLOWS down, as it approaches the a-particles gold nucleus, due to coulombian repulsion force between nucleus and `alpha`-particle. The `alpha` -particle can come up to a certain minimumdistance is calledthe distanceof closed approach . Obviously valueof distanceof closest approach provides the upperlimit onthe SIZE of thenucleus . 
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