Particles and radiation

• Specific charge


  Charge (C) / Mass (kg)
• The word "Specific' in physics means per unit mass
• Nucleus


  • Held together by the strong nuclear force
  • Strong nuclear force has a very short range, 4fm
  • At longer distances, the repulsive electromagnetic force dominates
  • At shorter distances, 0.5fm, the strong nuclear force becomes repulsive to stop protons & neutrons being pushed into each other
• Electromagnetic spectrum


  The entire range of EM waves (radiations)
• Properties of EM radiation

  • All consist of vibrating magnetic & electric waves, both are in phase, they vibrate together
  • All EM waves are transverse, the vibrations are at right angles to the direction of the waves motion
  • All travel with the same speed (3.00 x10 ms-1) in a vacuum
• Photon


  Packets of energy carried by EM waves
• Max Planck (1901) concluded that energy carried by light and other types of electromagnetic radiation existed in discrete packets called quanta
• Energy of a photon

  E = hf, where h is Planck's constant and f is the frequency
• In 1909 Einstein proposed that light radiation consists of a stream of quants called photons
• Laser power


  Power = nhf, where n is the number of photons emitted per second
• Electron volt (eV)


  The energy gained by an electron when it is moved through a potential difference of 1 volt
• Rest energy


  The energy locked up as mass, given by E = mc²
• The existence of antimatter was predicted by English physicist Paul Dirac in 1928
• Particle-antiparticle pair


  They have the same mass but opposite charge, and annihilate each other when they meet, converting their rest-mass into photons of gamma radiation
• Calculating frequency of gamma rays from particle-antiparticle annihilation

  1. Equate the photon energy to the mass energy of the positron-electron pair

  2. Use E = mc² to calculate the frequency
• Pair production


  A photon creates an electron-positron pair and disappears in the process
• Fundamental particles


  • Leptons
  • Hadrons
• Leptons


  • Fundamental particles with no substructure
  • Have lepton number 1
  • Have baryon number 0
  • Have strangeness 0 (no strange quarks)
  • Neutrinos have no charge
• Leptons


  • Electron
  • Muon
  • Electron neutrino
  • Muon neutrino
• Antileptons


  • Positron
  • Antimuon
  • Electron antineutrino
  • Muon antineutrino
• Hadrons


  • Not fundamental, contain quarks
  • Consist of two families: baryons and mesons
• Types of quarks


  • Down quark (d)
  • Anti-down quark (d-bar)
  • Up quark (u)
  • Anti-up quark (u-bar)
  • Strange quark (s)
  • Anti-strange quark (s-bar)
• Baryons


  • Contain three quarks
  • Have baryon number 1
  • Have lepton number 0
  • Have strangeness 0
• Baryons


  • Proton (uud)
  • Neutron (udd)
• Mesons


  • Contain one quark and one antiquark
  • Have baryon number 0 (not baryons)
  • Have lepton number 0 (not leptons)
  • Decay into photons and leptons
• Mesons


  • Pions
  • Kaons
• Pions


  • Contain a quark-antiquark pair
  • Have strangeness 0
• Kaons


  • Contain a strange quark or antiquark and either an up or down quark or antiquark
  • Have strangeness ±1
• In any interaction, the total lepton number is conserved
• The conservation rule must be applied to each lepton family in any interaction
• Atomic number = Number of protons
• Mass number = Number of protons + Number of neutrons
• Isotopes are atoms with different numbers of neutrons but the same atomic number.
• Radioactive decay involves unstable nuclei emitting particles until they become stable.
• Alpha (α) decay occurs when a heavy nucleus decays into two lighter ones by ejecting a helium nucleus (2 protons and 2 neutrons). The mass number decreases by four units and the charge decreases by four units.
• Alpha (α) decay occurs when an atom loses two electrons and four neutrons, resulting in a helium-4 nucleus being ejected from the parent nucleus.
• Beta (-β-) decay can occur through either electron emission or positron emission, depending on whether the parent nucleus has more or fewer neutrons than protons.
• Gamma (γ) rays are high energy photons that result from nuclear transitions between excited states.
• Beta minus (β-) decay is where an electron is emitted from the nucleus, resulting in a change in the atomic number by one unit and no change in the mass number.
• Beta (-β-) decay is where a neutron inside the nucleus turns into a proton, releasing an electron and an antineutrino.