particles & radiation

• 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
• Baryons


  Have three quarks
• Mesons


  Have a quark and an antiquark
• Four fundamental forces


  • Electromagnetic
  • Strong nuclear
  • Weak
  • Gravity
• Electromagnetic force


  Gauge boson is the virtual photon
• Strong nuclear force


  Gauge boson is the pion, keeps nucleus together
• Weak force


  Gauge bosons are W+ and W-
• Gravity


  Gauge boson is the hypothetical graviton
• Mass and energy are interchangeable, described by E=mc^2
• Annihilation


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


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


  • Alpha
  • Beta
  • Gamma
• Alpha particle


  Helium nucleus, highly ionizing but weakly penetrating
• Beta particle


  Fast moving electron, medium ionizing and penetrating
• Gamma ray


  High energy photon, weakly ionizing but highly penetrating
• Alpha decay


  Nucleus emits an alpha particle (helium nucleus)
• Beta decay


  Neutron turns into proton, electron and antineutrino emitted
• Conservation rules: charge, lepton number, baryon number must be conserved
• Strangeness is only conserved in strong interactions
• Muon


  Heavy electron
• Lepton number


  Electrons and neutrinos have +1, positrons have -1
• Isotopes


  Same element (same protons) but different number of neutrons
• Specific charge


  Charge to mass ratio, usually a very large number
• Electron volt


  Energy of an electron accelerated through 1 volt, 1.6x10^-19 J
• Photoelectric effect


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


  Proved light has a particle nature, not just wave nature
• Measuring kinetic energy of photoelectrons


  Use stopping potential to counteract kinetic energy
• De Broglie wavelength


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


  Electrons diffract around atoms, producing interference pattern
• Fluorescent tube


  Electrons emitted from cathode, excite mercury atoms, emit UV, which then excites 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 spectrum


  Wavelengths absorbed by a gas when shone through it
• Emission spectrum


  Wavelengths emitted by a light source