Particles

• What are the three constituents of an atom?

  Protons, neutrons and electrons
• Where is the nucleus of an atom located?

  At the centre of the atom
• What are protons and neutrons in the nucleus called?

  Nucleons
• What is the charge of a proton, neutron and electron in relative units?

  +1, 0, -1
• What is the mass of a proton, neutron and electron in relative units?

  1, 1, 0.0005
• What is the specific charge of a proton, neutron and electron?

  $9.58 \times 10^7 \text{ C/kg}$, 0 $\text{C/kg}$, $1.76 \times 10^{11} \text{ C/kg}$
• What is the proton number (Z) and nucleon number (A) of an atom?

  Z is the number of protons, A is the number of protons and neutrons
• What are isotopes?

  • Atoms with the same number of protons but different numbers of neutrons
  • For example, carbon-14 is a radioactive isotope of carbon
• How does carbon dating work?

  • Carbon-14 is a radioactive isotope of carbon
  • All living things have the same starting amount of carbon-14
  • As an object ages, the amount of carbon-14 decreases due to radioactive decay
  • By measuring the remaining carbon-14, the age of the object can be calculated
• What force keeps nuclei stable?

  The strong nuclear force
• How does the strong nuclear force vary with distance?

  It is attractive up to 3 fm and repulsive below 0.5 fm
• What type of decay occurs in nuclei with too many protons and neutrons?

  Alpha decay
• What happens to the proton number and nucleon number in alpha decay?

  The proton number decreases by 2, the nucleon number decreases by 4
• Why was the neutrino hypothesized in beta-minus decay?

  To account for the missing energy observed in the decay
• What is the relationship between a particle and its antiparticle?

  They have the same mass and rest energy but opposite properties
• What is the relationship between the energy of a photon and its frequency?

  The energy is directly proportional to the frequency
• How does annihilation work?

  • A particle and its antiparticle collide
  • Their masses are converted into energy
  • This energy, along with their kinetic energy, is released as two photons moving in opposite directions to conserve momentum
• How does a PET scanner work?

  • A positron-emitting radioisotope is introduced into the patient
  • Positrons annihilate with electrons, emitting gamma photons
  • The gamma photons are detected to create a 3D image of the inside of the body

  
• What is the requirement for pair production to occur?

  The photon energy must be greater than the total rest energy of the particle-antiparticle pair
• What are the four fundamental forces and their exchange particles?

  • Strong nuclear force: Gluons
  • Weak nuclear force: W and Z bosons
  • Electromagnetic force: Virtual photons
  • Gravitational force: Gravitons (not on specification)
• How do the weak nuclear force interactions of electron capture and electron-proton collision differ?

  They use different exchange particles (neutrino vs W boson)
• What is the difference between hadrons and leptons?

  Hadrons experience the strong nuclear force and are made of quarks, while leptons do not experience the strong force and are fundamental particles
• What are the different types of hadrons?

  • Baryons (3 quarks)
  • Antibaryons (3 antiquarks)
  • Mesons (quark-antiquark pair)

  
• What is the only stable baryon?

  The proton
• What are the two types of lepton number that must be conserved?

  Electron lepton number and muon lepton number
• What are strange particles and how do they decay?

  Strange particles are produced by the strong force but decay via the weak force, such as kaons decaying into pions
• Why do scientific investigations in particle physics rely on international collaboration?

  Particle accelerators are very expensive to build and run, and produce huge amounts of data
• What are the properties of the up, down and strange quarks?

  • Up (u) quark: Charge = +2/3, Baryon number = +1/3, Strangeness = 0
  • Down (d) quark: Charge = -1/3, Baryon number = +1/3, Strangeness = 0
  • Strange (s) quark: Charge = -1/3, Baryon number = +1/3, Strangeness = -1
• What are the quark combinations for different mesons?

  • π⁰: uu or dd
  • π⁺: ud
  • π⁻: du
  • k⁰: ds or ds
  • k⁺: us
  • k⁻: us

  
• What is the equation for the decay of a neutron?

  n → p + e− + νe
• What properties must be conserved in particle interactions?

  • Energy and momentum
  • Charge
  • Baryon number
  • Electron lepton number
  • Muon lepton number
  • Strangeness (only in strong interactions)
• How do the quark changes in beta-minus and beta-plus decay show they are weak interactions?

  In beta-minus decay a down quark changes to an up quark, and in beta-plus decay an up quark changes to a down quark, which involves a change in quark type