Particle physics

• Rutherford scattering 


  Fired alpha particles at a thin piece of gold leaf and most particles passes through the gold leaf, but some were deflected at large angles.

  The strong deflections were caused by electrostatic repulsion between the positive nucleus and positive alpha particles.

  Most of the particles passed through as the atom is mostly free space
• Antiparticle 


  oppositely charged
• Antiparticle of electron 


  Positron
• Annihilation 


  When particle and antiparticle collide, masses converted into pure energy producing a pair of gamma photons
• pair production 


  one high energy photon spontaneously turns into a particle-antiparticle pair
• Hadrons 


  Made of quarks
• proton is made up of 


  2 up quarks and down quark
• neutron made up of 


  One up quark and 2 down quarks
• mesons 


  type of hadron containing two quarks
• Baryon number is always conserved
• each lepton number is conserved separately
• Baryons 


  Contain 3 quarks
• stable baryon 


  proton is only stable
• leptons 


  not made of any smaller particles and do not feel strong nuclear force
• Lepton example


  Electrons
• muon 


  example of lepton

  negatively charged and heavier than electrons and unstable and always decay into electrons.
• fentometre

  10^-15 m
• Strong nuclear force acts on

  Nucleons and all quarks
• Weak nuclear force acts on

  Beta decay
• EMF acts on

  Particles with charge

  Infinite range