PMT: 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
• 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. Occurs in large nuclei with too many of both protons and neutrons

  2. Proton number decreases by 2

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


  1. Occurs in nuclei which are neutron-rich

  2. Proton number increases by 1

  3. 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 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)
• Proton

  Only stable baryon, 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
• Kaons

  Strange particles that decay into pions through the weak interaction
• Strangeness

  Property of particles, 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⁻ (du)
  • k⁰ (sd)
  • k⁺ (su)
  • k⁻ (su)
• Neutron decay


  n → p + e- + νe
• Energy, momentum, charge, baryon number and lepton number must always be conserved in particle interactions
• Types of quarks and antiquarks

  • Up (u)
  • Down (d)
  • Strange (s)