2.1 Particles

• What are the subatomic particles?

  Proton, Neutron and Electron
• What is meant by specific charge?

  The charge:mass ratio

  
  

  Specific Charge = Charge / Mass

  
  

  Units: C/kg or Ckg^-1
• What is the mass of a proton and a neutron?

  Both are 1.67*10-27kg
• What is the mass of an electron?

  9.11*10^-31kg
• What is the charge on a proton and an electron?

  Proton: 1.6*10^-19

  Electron: -1.6*10^-19
• What is the letter associated with a proton number?

  Z
• What is a nucleon?

  Number of protons + number of neutrons
• Which letter represents nucleon number?

  A
• What is an isotope?


  A version of an element with the same number of protons but a different number of neutrons
• What is the strong nuclear force?

  The fundamental force that keeps the nucleus stable by counteracting the electromagnetic force of repulsion between protons
• Describe the range of the strong force

  Repulsive up to 0.5fm

  Attractive from 0.5fm - 3fm

  Negligible past 3fm
• What makes a nucleus unstable?

  Nuclei which either have too many neutrons, too many protons or both
• How do nuclei with too many nucleons decay?

  Alpha Decay (4,2)
• How do nuclei with too many neutrons decay?

  Beta minus decay in which a neutron decays to a proton by the weak interaction (quark character has changed from udd to uud)
• How was the existence of the neutrino hypothesised?

  The energy of particles after beta decay was lower than before, a particle with 0 charge (to conserve charge) and negligible mass must carry away the excess energy, known as a neutrino
• What is meant by beta minus decay?

  When a neutron turns into a proton, the atom releases an electron and an anti-electron neutrino
• What is an 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.
• What is the antiparticle of pi 0?

  pi 0 (itself)
• What occurs when a particle and antiparticle meet?

  Annihilation
• What is 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.
• What is pair production?

  A gamma ray photon is converted into a particle-antiparticle pair.
• Name the four fundamental forces

  Strong Nuclear

  Weak Nuclear

  Electromagnetic

  Gravitational
• The visual photon is the exchange particle of which fundamental force?

  The electromagnetic force
• What type of particles are affected by the strong nuclear force?

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

  W boson (W+ or W-)
• What does the electromagnetic force act on?


  It acts on charged objects, for example when a positively charged ball repels another positively charged ball.
• When does the weak nuclear reaction occur?

  When quark character changes (one quark turns into another quark), it affects all types of particles
• Which properties must be conserved in particle interactions?

  Energy, charge, lepton number (electron), lepton number (muon), baryon number, strangeness (only in strong interactions)
• What is a hadron?

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

  Baryons - 3 quarks

  Mesons - Quark-antiquark pair
• The pion and kaon are both examples of which class of particle?

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

  The strong nuclear force
• What particle does a kaon decay into?

  A kaon decays into a pion
• What is significant about a proton?

  It is the only stable baryon

  All baryons will eventually decay into protons
• What does a muon decay into?

  An electron and two types of neutrino