Particles Salman A Level

• Fundamental particles


  • Leptons
  • Hadrons
• Leptons


  Fundamental particles including electron, muon, and neutrino
• Electron number

  1 for leptons, -1 for antiparticles
• Neutrinos


  Can be electron neutrinos or muon neutrinos
• Quark flavours


  • Up
  • Down
  • Strange
• Strangeness


  • 1 for strange quark, +1 for anti-strange
• Electromagnetic force


  • Affects any charged particle, exchange particle is photon
• Weak force


  • Affects any particle, exchange particles are W+, W-, Z0 bosons
• Strong force


  • Affects hadrons only, exchange particle is gluon
• Electrostatic repulsion between protons


  Pushes outwards
• Strong force


  Pulls inwards
• When forces are balanced, nucleus is stable
• Range of strong force

  1. 4 fm, switches from attractive to repulsive at 0.5 fm
• In any interaction, charge, baryon number and lepton number must be conserved
• Feynman diagrams


  Represent interactions, always a weak interaction for beta decay
• One down quark in neutron decays to up quark, turning neutron into proton
• Strangeness rules


  • Interactions with leptons are weak
  • Interactions with hadrons and conserved strangeness are strong
  • Interactions with hadrons and non-conserved strangeness are weak
• Charge


  Charge to mass ratio, unit is C/kg
• Radiation is any particle or wave emitted by something
• Types of radiation emitted by nuclei

  • Gamma radiation (high energy EM waves)
  • Alpha radiation (helium nucleus)
  • Beta radiation (high energy electron)
• Heavier nuclei are generally more unstable and likely to decay
• Alpha decay


  1. Nucleus emits helium nucleus (2 protons, 2 neutrons)

  2. Daughter nucleus has lower atomic number
• Beta decay


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

  2. Daughter nucleus has higher atomic number
• Electron-positron annihilation produces two photons
• Minimum energy/frequency of photons from annihilation

  Equal to 2mc^2 (rest energy of particles)
• Pair production


  Photon with sufficient energy converts into particle-antiparticle pair
• Electron energy levels in atoms

  Discrete levels, with ground state as lowest energy
• Electron excitation and de-excitation

  1. Electron can be excited to higher level by collision or photon absorption

  2. Electron then de-excites, emitting photon(s)
• Ionization


  Electron can be excited to ionization level, leaving atom as positive ion
• Energy levels


  Can be expressed in Joules or electron volts (1 eV = 1.6x10^-19 J)
• Emission spectrum


  Diagram showing wavelengths of photons emitted by an object, used to determine composition
• Absorption spectrum


  Diagram showing wavelengths absorbed by a gas or plasma, also used for composition analysis
• Fluorescent tube lights


  1. Electrons accelerated through mercury gas, causing UV emission

  2. UV absorbed by fluorescent coating, re-emitted as visible light
• Light has wave-particle duality
• Photoelectric effect


  1. Light shone on metal causes electrons to be liberated

  2. Kinetic energy of ejected electrons depends on photon frequency, not intensity
• Work function


  Minimum energy required to liberate an electron from a metal surface
• Photoelectric effect proves light acts as particles (photons)
• Electron diffraction


  Electrons passing through graphite produce interference pattern, proving wave nature
• de Broglie wavelength


  Wavelength of a particle, inversely proportional to momentum
• Atom


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