2.1 particles

• Specific charge = total charge of particles / total mass of particles

  
  

  Isotopes - an atom of an element with the same number of protons but different number of neutrons; same atomic number but different nucleon number

  
• Electrostatic force - the result of an interaction between a charge with the electric field produced by another charge

  • Has infinite range
  • Is only felt by charged particles

  Strong nuclear force - counteracts electrostatic force of positive nucleons trying to repel each other

  • Has a very short range
  • Is felt by all nucleons
  • Repulsive at very small separations

  
• Neutrino - v

  • Subatomic particle similar to an electron that accounts for conservation of energy in beta decay
  • Have no charge
  • Have negligible mass, 1.25 x 10-37
  • Nearly impossible to detect 
  • Anti-neutrino - (^-v)

  
• Antiparticles - a subatomic particle with identical mass and energy as a given particle but with opposite electric or magnetic properties

  • An unstable particle and its antiparticle have the same lifetime
  • Some neutral particles and their antiparticles are identical 
  • Others have different features that are opposite like spin

  
• Rest mass - mass of a stationary particle

  $E =$$mc^2$

  Rest energy E0 - the energy equivalent of the mass of a stationary particle

  Energy of a moving particle = rest energy + moving energy

  $E =$$mc^2 +$$1/2(mass * v^2)$
• ElectronVolt - eV

  • The energy required to accelerate an electron across a potential difference of 1 volt
  • E = v x Q

  1 eV = 1.6 x 10-19J

  
• Photon - a quanta or packet of light of a certain energy

  • A photon of wavelength 400nm has energy of 4.97 x 10-19J

  Photon emission

  • The stopping, slowing down, or change of direction of a fast moving electron
  • An electron moving from a high energy shell to low energy shell
• Energy levels

  Particle E= mc2

  • energy is equivalent to a particle’s mass when travelling at the speed of light

  Photon E = hf 

  • energy is planck’s constant times the photon’s frequency
  • Planck’sck’s constant - 6.6310-31

  Speed of light E = hc

  • c =f, or f = c
  • Speed of light = frequency x wavelength
• Lasers - Monochromatic light

  Power P = nhf

  • Power is number of photons per second x Planck’s constant x frequency

  P= nhf / wavelength

  Power = (number of photons per second x planck's constant x speed of light) / wavelength
• Annihilation

  If a particle collides with its antiparticle, they annihilate each other and their mass separates as two photons with equal energy

  • E_0=2mc^2
  • E = 2hf
  • mc^2 = hf
  • E_min = 2E_0

  
• Fundamental interaction forces

  • Strong nuclear 
  • Weak forces
  • Electrostatic
  • Gravitational 

  Exchange particles 

  • Virtual particles / gauge bosons
  • Short lived
  • Each fundamental reaction has its own boson that can transfer momentum, energy, and charge
• Hadrons

  • Feel strong nuclear force
  • Not fundamental particles
  • E.g. protons and neutrons

  Leptons 

  • Feel weak nuclear force
  • Are fundamental particles
  • E.g. electrons and neutrinos

  
• Feynman diagram

  • Particle interaction diagram
  • Straight lines represent particles
  • Gauge bosons are represented by ‘wiggly lines’
  • Hadrons are always on the left
  • Leptons are always on the right
  • Time goes from top to bottom
  • All lines must be connected 
  • Two lines connect to either side of the ‘wiggly line’

  
• Hadrons

  • Stout and thick
  • Feels a strong force
  • Not fundamental particles
  • Formed from quarks
  • Only quarks feel the strong force
• Baryons

  • Heavy
  • Forms from three quarks
  • Baryon number of 1
  • All decay via weak interaction
  • All are unstable except proton
  • Protons
  • Neutrons

  Mesons

  • Intermediate
  • Formed from 2 quarks
  • Baryon number of 0
  • All decay via weak interaction
  • All are unstable
  • All produced in pairs
  • Pions
  • Kaons K (strange)
• Leptons

  • Fine, small, thin
  • Dont experience the strong force 
  • Fundamental particles
  • Dont contain quarks
  • All have lepton number of 1
• Electrons

  • Mass 0.511MeV
  • Charge -1
  • e+, e-

  Electron neutrino

  • Mass < 2eV
  • No charge Ve

  Muon

  • 200 x Me
  • Charge -1
  • Decays to electron + 2 neutrinos
  • +, -

  Muon neutrino

  • Mass < 0.2MeV
  • No charge
  • V

  Tau 

  • 3500 x Me
  • Charge -1
  • Decays quickly
  • +, -

  Tau neutrino

  • Mass < 18MeV
  • No charge
  • V
• In baryons, quarks are either all matter or all anti-matter

  
• Quark combinations

  Proton - u u d

  Antiproton - u u d

  Neutron - u d d

  Antineutron - u d

  Kaon+ - s u

  • Strange with +1

  Kaon- - s u

  • Strange with -1 charge

  Kaon0 - s d

  • Strange with 0 charge

  Pion+ - u d

  Pion- - u d

  Sigma+ - s u u

  Sigma- - s d d

  • Baryon with -1 charge/strangeness

  Sigma0 - s u d

  Delta+ - u u d

  Delta- - d d d

  Delta0 - u d d

  Strangeness - particles take less time to decay

  
• Conservation laws

  • Particle interactions are possible if certain quantum numbers are conserved
  • Charge
  • Lepton and baryon number
  • Strangeness (only in strong interaction)

  Weak interaction 

  Occurs if any of the following applies

  • There are leptons involved
  • Total strangeness changes
  • Quarks change
  • W+ or W- exchange particles are present

  If there are none, the strong interaction occurs

  • Changing flavour happens due to the weak interaction
• Strangeness

  • Particles with strange or anti-strange quarks - e.g. kaons
  • Strange particles always share properties
  • Are produced through strong interaction
  • Decay through the weak interaction