3.2.1 Particles

3.2.1 Particles

1. Constituents of the atom

   • p, n, e
   • isotopes
     • different number of neutrons
       • different A number (top number)
   • specific charge = charge / mass
     • unit - C kg^(-1)
   • atomic mass unit

2. Stable and unstable nuclei

   • strong nuclear force
     • overcomes electrostatic force of repulsion between protons in the nucleus and keeps the protons and neutrons together
     • range no more than 3-4 fm
     • attractive force from 3-4 fm to 0.5 fm
   • unstable nuclei and radioactive decay
     • beta decay
       • neutron changes into proton
         • when nuclei have too many neutrons
     • gamma radiation emitted when nucleus has too much energy following an alpha or beta emission
     • neutrino needed for conservation of energy

3. Particles, antiparticles, and photons

   • each type of particle has a corresponding antiparticle
   • photon energy, E = hf = hc / λ
   • Photon
     • wave packet of em radiation
   • rest energy, E = mcc
   • particle and corresponding antiparticle
     • annihilate if they meet
       • mass converted to photons
         • minimum energy of each photon produced, hf min = E0
     • have exactly the same rest mass
     • have exactly the opposite charge
     • pair production
       • photon with sufficient energy passing near a nucleus or an electron can suddenly change into a particle-antiparticle pair, which would then separate from each other
         • minimum energy of photon needed = hf min = 2E0
   • 1Mev = 1.60 x 10^(-13) J

4. Particle interactions

   • strong
     • hadrons subject to strong
   • strong nuclear force
     • pion is exchange particle
   • strange particles produced through strong, and decay through weak
     • strangeness can change by 0, +1, or -1 in weak interactions
   • gravity, em, weak, strong
   • em
     • virtual photon is exchange particle
   • weak
     • limited to beta minus and beta plus decay, electron capture, and electron-proton collisions
     • W+ and W- as exchange particles
   • Feynman diagram

5. Classifications of particles

   • particle zoo
   • proton is the only stable baryon into which other baryons eventually decay
   • kaon decays into pions
   • muon decays into electron

6. Quarks and antiquarks

   • table in formula booklet

7. Applications of conservation laws

   • know how quarks change in beta minus and plus decay
   • energy and momentum are conserved in interactions

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