PMT: particles (flashcards)

• Proton

  One of the main constituents of an atom
• Neutron

  One of the main constituents of an atom
• Electron

  One of the main constituents of an atom
• Specific charge

  The charge to mass ratio: Specific charge = charge / mass. Units C/kg.
• Protons have charge +1.6 x10^-19 and mass 1.67 x 10^-27 kg. Specific charge = 1.6 x 10^-19/1.67 x 10^-27 = 9.58 x 10^7 C/kg
• Proton number

  Represented by the letter Z
• Nucleon

  A constituent of the nucleus: a proton or a neutron
• Nucleon number

  Represented by the letter A
• The correct notation is X A Z
• Isotope

  A version of an element with the same number of protons but a different number of neutrons
• Use of radioactive isotopes

  • Carbon dating - the proportion of carbon-14 in a material can be used to estimate its age
• Strong nuclear force

  The fundamental force that keeps the nucleus stable by counteracting the electrostatic force of repulsion between protons
• Range of the strong force

  • Repulsive up to 0.5fm, Attractive from 0.5-3fm, Negligible past 3fm
• Unstable nucleus

  Nuclei which have too many of either protons or neutrons or both
• Alpha decay

  Emission of a helium nucleus formed of 2 protons and 2 neutrons
• Beta minus decay

  A neutron turns into a proton, the atom releases an electron and an anti-electron neutrino
• Alpha particle

  A particle contains two protons and two neutrons, the same as a helium nucleus
• Antiparticle

  For each particle there is an antiparticle with the same rest energy and mass but all other properties are the opposite of its respective particle
• Every particle has an antiparticle
• Positron


  The antiparticle of an electron
• The antiparticle of π0 (pion with 0 charge) is π0, its antiparticle is itself
• Annihilation

  When a particle and antiparticle meet, the mass of the particle and antiparticle is converted back to energy in the form of 2 gamma ray photons which go in opposite directions to conserve momentum
• Pair production

  A gamma ray photon is converted into a particle-antiparticle pair
• The minimum energy of a photon required to make a proton-antiproton pair is 2 x proton rest energy, 2 x 938.257 = 1876.514 MeV
• 4 fundamental forces

  • Gravity
  • Electromagnetic
  • Strong nuclear
  • Weak nuclear
• Annihilation

  The mass of the particle and antiparticle is converted back to energy in the form of 2 gamma ray photons which go in opposite directions to conserve momentum
• The minimum energy of a photon required to make a proton-antiproton pair is 2 x proton rest energy (2 x 938.257 = 1876.514 MeV)
• Fundamental forces

  • Gravity
  • Electromagnetic
  • Weak nuclear
  • Strong nuclear
• Virtual photon

  The exchange particle of the electromagnetic force
• Strong nuclear force

  Acts on hadrons
• Weak nuclear force

  Exchange particle is the W boson (W+ or W-)
• Electromagnetic force

  Acts on charged objects
• Weak nuclear interaction

  Occurs when quark character changes (a quark changes into another quark), it affects all types of particles
• Properties that must be conserved in particle interactions

  • Energy
  • Charge
  • Baryon number
  • Lepton number
  • Momentum
  • Strangeness (only for strong interactions)
• Hadron

  Both baryons and mesons are hadrons, hadrons are made of 2 or more quarks held together by the strong nuclear force
• Classes of hadrons

  • Baryons (three quarks)
  • Mesons (1 quark, 1 antiquark)
• Pion and kaon are both examples of mesons
• Pion

  Can be an exchange particle for the strong nuclear force
• A kaon decays into a pion
• Baryons

  • Proton - uud
  • Neutron - ddu