02: Particles And Radiation

• Atom


  Formed of 3 constituents: protons, neutrons and electrons
• Nucleus


  Formed of protons and neutrons, also known as nucleons
• Electrons


  Orbit the nucleus in shells
• Particle properties


  • Charge
  • Mass
  • Specific charge

  
• Proton number


  Number of protons in an atom
• Nucleon number


  Number of protons and neutrons in an atom
• Isotopes


  Atoms with the same number of protons but different numbers of neutrons
• Carbon-14


  Radioactive isotope of carbon used in carbon dating
• Carbon dating


  Calculating the percentage of carbon-14 remaining in an object to determine its approximate age
• Strong nuclear force (SNF)

  Keeps nuclei stable by counteracting the electrostatic force of repulsion between protons
• Unstable nuclei


  • Have too many of either protons, neutrons or both, causing the SNF to not be enough to keep them stable
• Alpha decay


  1. Proton number decreases by 2

  2. Nucleon number decreases by 4
• Beta-minus decay


  1. Proton number increases by 1

  2. Nucleon number stays the same
• Neutrinos were hypothesised to account for the lack of energy conservation in beta-minus decay, and later observed

  
• Antiparticle


  Has the same rest energy and mass but all other properties are opposite the particle
• Photon


  Packets of electromagnetic radiation that transfer energy and have no mass
• Annihilation


  Particle and antiparticle collide, converting their masses into energy released as 2 photons

  
• Pair production


  Photon is converted into an equal amount of matter and antimatter
• Fundamental forces


  • Gravity
  • Electromagnetic
  • Weak nuclear
  • Strong nuclear
• Exchange particles


  Carry energy and momentum between particles experiencing a force
• Exchange particles for each fundamental force

  • Gluon (strong)
  • W boson (weak)
  • Virtual photon (electromagnetic)
  • Graviton (gravity)
• Electron capture


  p + e- → n + νe
• Electron-proton collision


  p + e- → n + νe
• Beta-plus decay


  p → n + e+ + νe
• Beta-minus decay


  n → p + e- + νe
• Hadrons


  Particles that experience the strong nuclear force, formed of quarks
• Leptons


  Fundamental particles that do not experience the strong nuclear force
• Types of hadrons


  • Baryons
  • Antibaryons
  • Mesons
• Baryon number


  Shows whether a particle is a baryon (1), antibaryon (-1) or not a baryon (0)
• The proton is the only stable baryon, so all baryons will eventually decay into a proton
• Lepton number


  Shows whether a particle is a lepton (1), antilepton (-1) or not a lepton (0)
• Muon


  Heavy electron that decays into an electron
• Strange particles


  Produced by the strong nuclear interaction but decay by the weak interaction
• Strangeness


  Property of particles that must be conserved in strong interactions but can change in weak interactions
• Scientific investigations in particle physics rely on international collaboration due to the high cost and data output of particle accelerators
• Types of quarks


  • Up (u)
  • Down (d)
  • Strange (s)
• Quark combinations for mesons

  • π⁰ (uu or dd)
  • π⁺ (ud)
  • π⁻ (ud)
  • k⁰ (ds or ds)
  • k⁺ (us)
  • k⁻ (us)
• Neutron decay


  n → p + e- + νe
• Properties that must be conserved in particle interactions

  • Energy and momentum
  • Charge
  • Baryon number
  • Lepton number
• Quarks


  Fundamental particles which make up hadrons