Inside the atom

Inside the atom

1. Structure

   • So small, need an electron microscope to see them
   • Alpha scattering investigation - Rutherford
     • Showed
       • Positive nucleus
         • Protons
         • Neutrons
       • Electrons surrounding nucleus
         • Negative charge (-1.6x10^-19 C)
         • Held by electrostatic attraction
     • Procedure
       • Alpha particles at gold foil
       • Most went through undetected
       • Some were deflected back at large angles
       • Small number deflected backwards
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2. Isotopes

   • Different numbers of neutrons
   • Nucleon number - Protons and neutrons, mass number

3. Specific charge

   • Charge/Mass

4. Strong nuclear force

   • Force holding nuclei together
   • Overcomes electrostatic force of repulsion between protons
   • Keeps protons and neutrons together (in stable nuclei)
   • Range no more than 3-4fm
     • Diameter of small nucleus
   • Has the same effect on two protons as on two neutrons
   • Attractive force from 3-4fm down to about 0.5fm
     • At separation smaller than this, it is repulsive and prevents protons and neutrons being pushed into eachother

5. Radioactive decay

   • Alpha radiation
     • Helium nucleus released (2 p 2 n)
   • Beta radiation
     • Fast moving electrons
       • Charge equal and opposite to the proton
     • Neutron becomes a proton
     • Antineutrino emitted
   • Gamma radiation
     • EM radiation
     • Can pass through thick metal plates
     • No mass or charge
     • Emitted from a nucleus with too much energy, after alpha or beta emission

6. Elusive particle

   • Energy spectrum of beta particles measured
     • Energy appeared not to be conserved
       • Actually carried away by particles
   • Particles were called neutrinos or anti neutrinos
   • Detected due to their interaction with cadmium nuclei in a large tank of water