Particles and radiation

• Atom


  Has a small nucleus located in the center containing protons and neutrons, with electrons orbiting the nucleus
• Proton


  • Charge of +1.6 x 10^-19 C
  • Mass of ~1.67 x 10^-27 kg
• Neutron


  • No charge
  • Mass of ~1.67 x 10^-27 kg
• Electron


  • Charge of -1.6 x 10^-19 C
  • Mass of ~9.11 x 10^-31 kg
• Atomic notation


  • Element symbol (X)
  • Proton number (Z)
  • Nucleon number (A)
• Isotopes


  • Hydrogen-1
  • Deuterium
  • Tritium
• Isotopes have the same number of protons but different numbers of neutrons
• Radioactive carbon dating


  • Living things contain a constant ratio of carbon-14 to carbon-12
  • After death, the ratio of carbon-14 to carbon-12 decreases
  • Physicists can use the percentage of carbon-14 left to calculate the age
• Specific charge


  Ratio of charge to mass of a particle, measured in C/kg
• Nuclear forces


  • Gravity (weak)
  • Electrostatic repulsion (large)
  • Strong nuclear force (binds nucleus)
• Alpha decay


  1. Nucleus emits alpha particle (2 protons, 2 neutrons)

  2. Decreases proton number by 2, decreases nucleon number by 4
• Beta minus decay


  1. Neutron turns into proton, emits electron and antineutrino

  2. Increases proton number by 1, nucleon number stays the same
• Antiparticles


  Have the same mass but opposite charge as their corresponding particles
• Electron-positron annihilation


  • Electron and positron convert all their mass into photon energy
• Photon energy


  E = hf = hc/λ, where h is Planck's constant
• Maximum photon wavelength from electron-positron annihilation = 2.42 x 10^-12 m
• The minimum energy we can use is the energy conservation and we can estimate the wavelength of these photons because this is the minimum energy, the wavelength will be a maximum
• Calculating the maximum wavelength


  1. Input energy = 2 x 0.511 Mega electron volts

  2. Energy afterwards = 2 x energy of a photon

  3. Rearrange for wavelength

  4. Plug in values for H and C
• The opposite of annihilation is known as pair production
• Pair production


  1. Photon turns into a particle-antiparticle pair

  2. Minimum energy for this = at least twice the rest energy of the particles
• Fundamental forces


  • Electromagnetic force
  • Weak nuclear force (responsible for nuclear decay)
  • Strong nuclear force (holds the nucleus together)
  • Gravity
• Gravity is considerably weaker than the other three fundamental interactions and is often ignored in particle physics
• Virtual photon


  The exchange particle that carries the electromagnetic interaction
• Exchange particles for the fundamental forces are known as gauge bosons
• Virtual particles


  Real particles that exist for a very short time
• Feynman diagram for electromagnetic repulsion

  1. Two electrons repelling

  2. Virtual photon exchanged between them
• Feynman diagram for beta plus decay

  1. Proton turns into neutron, positron, and neutrino

  2. W+ boson released
• Feynman diagram for beta minus decay

  1. Neutron turns into proton, electron, and anti-neutrino

  2. W- boson released
• Feynman diagram for electron capture

  1. Proton captures electron, turns into neutron and neutrino

  2. W+ boson released
• Hadrons


  Particles affected by the strong nuclear interaction
• Baryons


  Hadrons with three quarks
• Mesons


  Hadrons with a quark-antiquark pair
• Baryon number


  Quantum number conserved in reactions, baryons have B=1, mesons have B=0
• Baryons are generally unstable, except for the proton
• Leptons


  Particles that don't interact with the strong nuclear force, e.g. electrons, muons, neutrinos
• Lepton number


  Quantum number conserved in reactions
• Quarks


  Fundamental particles that make up hadrons
• Quark properties


  • Up quark: +2/3 charge
  • Down quark: -1/3 charge
  • Strange quark: -1/3 charge
• Proton composition: 2 up quarks, 1 down quark
• Neutron composition: 2 down quarks, 1 up quark