quantum+particles AS

• Types of particles


  • Hadrons
  • Leptons
• Leptons


  Fundamental particles, examples are electron, positron, neutrinos
• Hadrons


  Can be split into baryons and mesons
• Baryons


  • Made of quarks
• Mesons


  • Made of a quark and an antiquark
• Quarks are fundamental particles as far as we know
• Baryons have three quarks, mesons have two quarks (a quark and an antiquark)
• Quarks are held together by the strong nuclear force
• Examples of baryons and mesons


  • Neutron
  • Proton
  • Pion
• Baryon number


  Conserved quantity for baryons
• Lepton number


  Conserved quantity for leptons
• Four fundamental forces


  • Electromagnetic (gauge boson: virtual photon)
  • Strong nuclear (gauge boson: gluon)
  • Weak (gauge bosons: W+, W-)
  • Gravity (hypothetical gauge boson: graviton)
• Strong nuclear force


  • Keeps nucleus together by overcoming electrostatic repulsion of protons
  • Has a short range of attraction, around 3-4 fm
• Mass-energy equivalence


  E = mc^2
• Annihilation


  Particle and antiparticle collide and are destroyed, energy converted to photons
• Pair production


  Photon with sufficient energy turns into a particle-antiparticle pair
• Types of ionizing radiation

  • Alpha
  • Beta
  • Gamma
• Alpha radiation


  • Highly ionizing, weakly penetrating, stopped by paper or few cm of air
• Beta radiation


  • Medium ionizing and penetrating, stopped by few mm of aluminium
• Gamma radiation


  • Weakly ionizing, highly penetrating, reduced by concrete
• Alpha decay


  Nucleus emits alpha particle (helium nucleus)
• Beta decay


  Neutron converts to proton, emitting electron and antineutrino
• Feynman diagram shows beta minus decay: neutron -> proton + W- -> proton + electron + antineutrino
• Conservation rules: charge, lepton number, baryon number conserved, strangeness conserved in strong interactions
• Muon


  Heavy electron
• Isotopes


  Same element, different number of neutrons
• Specific charge


  Charge to mass ratio
• Electron volt (eV)


  Energy gained by electron accelerated through 1 volt
• Photoelectric effect


  Photons of sufficient energy liberate electrons from metal surface
• Photoelectric effect


  Proved light has particle nature, not just wave nature
• Measuring photoelectron kinetic energy


  Use stopping potential to counteract electron kinetic energy
• De Broglie wavelength


  Wavelength associated with a particle, given by h/p
• Electron diffraction


  Electrons diffract around atoms, producing interference pattern
• Fluorescent tube


  Electrons emitted by cathode, excite mercury gas atoms, which emit UV photons that then excite phosphor coating to emit visible light
• Electron energy levels


  Electrons can be excited to higher levels by absorbing photons or collisions
• Ionization level


  Energy level where electron can escape atom/molecule completely
• Absorption and emission spectra


  Absorption spectrum shows what wavelengths are absorbed, emission spectrum shows what wavelengths are emitted