particles

• the strong nuclear force keeps the nucleus stable
• the strong nuclear force is attractive up to approximately 3 fm
• the strong nuclear force is repulsive closer than approximately 0.5 fm
• some atomic nuclei are unstable. the nucleus gives out radiation as it changes to become more stable. this is a random process called radioactive decay
• an alpha particle consists of two neutrons and two protons
• an alpha particle is the same as a helium nucleus
• a beta particle (β-) is a high speed electron ejected from the nucleus
• during beta-minus (β-) decay a neutron turns into a proton, emitting a beta-minus particle and an electron antineutrino in the process
• the existence of the neutrino was hypothesised to account for conservation of energy in beta decay
• for every type of particle there is a corresponding antiparticle
• the antiparticle of the proton is the antiproton
• the antiparticle of the neutron is the antineutron
• the antiparticle of the electron is the positron
• the antiparticle of the neutrino is the antineutrino
• a particle and its antiparticle have identical masses
• a particle and its antiparticle have opposite charge that are equal in magnitude
• a particle and its antiparticle have identical rest energies
• a photon is a packet or 'quantum' of electromagnetic waves
• the energy of a photon is directly proportional to its frequency

  $E=$$hf$
• the energy of a photon is inversely proportional to its wavelength

  $E=$$hc/λ$
• annihilation occurs when a particle and its corresponding antiparticle meet and their mass is converted into radiation energy in the form of two photons
• two photons are released (travelling in opposite directions) as a result of annihilation in order to conserve both momentum and energy
• following annihilation the minimum total energy of the two photons produced is equal to the total rest energy of the particle-antiparticle pair
• in pair production a photon creates a particle and its corresponding antiparticle providing that the photon has enough energy to produce their rest masses
• in order for pair production to occur the photon must have energy greater than the total rest energy of the particle-antiparticle pair produced. any excess energy is transferred to the kinetic energy store of the particles
• hadrons are subject to the strong force
• there are two classes of hadrons: baryons and mesons
• the proton is an example of a baryon

  uud
• the neutron is an example of a baryon

  udd
• the pion is an example of a meson

  π- = du ¯

  π+ = uu ¯, dd ¯

  π0 = ud ¯
• the kaon is an example of a meson

  K- = su ¯

  K+ = us ¯

  K0 = ds ¯, sd ¯
• baryon number must be conserved in all interactions
• the proton is the only stable baryon into which other baryons eventually decay into
• the pion is the exchange particle of the strong nuclear force
• the kaon is a particle that can decay into pions
• the electron is an example of a lepton
• the muon is an example of a lepton
• the electron neutrino is an example of a lepton
• the muon neutrino is an example of a lepton
• the antiparticle of the muon is the antimuon