Particles

• What are the main constituents of an atom?

  Proton, neutron, electron
• What is meant by specific charge?

  The charge to mass ratio: C = Q/m

  Units are C/kg.
• What is the charge of a proton?

  The charge of a proton is 1.6*10^-19 C.
• What is an isotope?


  A version of an element with the same number of protons but a different number of neutrons.
• State a use of radioactive isotope

  Carbon dating - the proportion of carbon-14 in a material can be used to estimate its age.
• What is the strong nuclear force?

  The fundamental force that keeps the nucleus stable by counteracting the electrostatic force of repulsion between protons.
• What is the range of the strong force?

  Repulsive from 0 to 0.5 fm, then attractive from 0.5 to 3fm. Past 3fm the force drops off rapidly.
• What makes a nucleus unstable?

  When they have too many protons or neutrons or both.
• How do nuclei with too many nucleons decay?

  Alpha decay.
• How do nuclei with too many neutrons decay?

  Beta minus decay. (Neutron decays to a proton by the weak interaction.)
• How was the existence of the neutrino hypothesised?

  The energy of particles after beta decay was lower than before, a particle of 0 charge and negligible mass must carry away this excess energy, hence the neutrino.
• What is beta minus decay?

  When a neutron turns into a proton, the atom releases an electron and an anti-electron neutrino.
• What is an alpha particle?

  A helium nucleus (2 protons, 2 neutrons).
• What is an antiparticle?


  For each particle there is an antiparticle with the same rest energy and mass but all the other properties are opposite.
• What is the antiparticle of a pion with 0 charge.

  A pion with 0 charge, it is itself.
• What happens when a particle and an antiparticle meet?

  They annihilate eachother: The mass of the particle and antiparticle are converted back to energy in the form of 2 gamma ray photons which go in opposite directions to conserve momentum.
• What is pair production?

  A gamma ray photon is converted into a particle-antiparticle pair.
• What is the minimum energy of a gamma ray photon to produce a proton-antiproton pair?

  2*proton rest energy = 2*938 = 1876 MeV
• What are the 4 fundamental forces?

  Gravitational force, electromagnetic force, strong nuclear force, weak nuclear force.
• The virtual photon is the exchange particle of which force?

  The electromagnetic force.
• Which types of particles are affected by the strong nuclear force?

  Hadrons
• What is the exchange particle of the weak nuclear force?

  A W boson.
• What does the electromagnetic force act on?

  Charged particles.
• When does the weak nuclear interaction occur?

  When quark character changes. It affects all particles.
• Which properties must be conserved in particle interactions?

  Charge, Baryon number, Lepton numbers, Energy, Momentum, Strangeness (only for strong interactions).
• What is a hadron?

  A particle made from quarks that is affected by the strong force. 
• What are the classes of hadrons?

  Baryons (3 quarks) and mesons (quark-antiquark pair).
• The pion and kaon are both examples of what?

  Mesons
• The pion can be an exchange particle for which force?

  Strong nuclear force.
• What particle does a kaon decay into?

  Pion
• Give some examples of baryons.

  Proton - uud

  Neutron - udd
• What is significant about a proton?

   It is the only stable baryon and all baryons will eventually decay into protons.
• What are some examples of leptons?

  Electron, muon, neutrino (and their antiparticles).
• What does a muon decay into?

  An electron, a neutrino and an antineutrino.
• What is the strangeness of a strange quark?

  -1
• How much can strangeness change by in the weak interaction?

  +1, -1, or 0 change.
• Strange particles are produced through which interaction?

  The strong interaction
• Strange particles decay through which interaction?

  The weak interaction.