Particles

Particles

1. Constituents of The Atom

   • Isotopes
     • Atoms of the same element with the same number of protons but a different number of neutrons
   • Specific Charge
     • How much charge a particle has for its mass

2. Stable and Unstable Nuclei

   • Strong Nuclear Force
     • An attractive force from 0.5fm to 3-4fm; a replusive force below 0.5fm
       • 1 fm =1x10^-9m
     • Only applies to all hadrons (particles which have a quark in them)
     • Keeps the nucleus stable, negates electrostatic repulsion of the protons with each other
       • As you go up the periodic table, elements with more protons need more neutrons to negate the electrostatic repulsion
   • Neutrinos
     • Beta minus decay is accompanied by the emission of an anti-neutrino
     • Hypothesised to account for conservation of energy in beta decay
     • Negligible mass
   • Nuclei decay (emit particles) to make itself more stable
     • Alpha Decay
       • Emission of a particle with two neutrons and two protons
     • Beta Decay
       • Emission of a beta-minus particle (electron) or a beta plus-particle (positron)

3. Particles, Anitparticles and Photons

   • Annihilation
     • For every type of particle, there is a corresponding antiparticle that:
       • Annihilates the particle and itself if they meet, converting their total mass into two photons
         • Two photons are produced to ensure that both momentum and energy are conserved
       • Has exactly the same mass as the particle
       • Has exactly opposite charge to the particle( if there is a charge)
       • Same ability to experience the same forces
   • Pair Production
     • A photon can interact with the high electric field an atom
       • The energy of the photon can be converted into a particle-antiparticle pair
         • The energy of the incident photon is equal to the mass (rest mass energy) and energy (kinetic) of the two particles produced
           • • Photon with sufficient energy that suddenly has changed into a particle-antiparticle pair (electron and positron)
   • Photons
     • A packet of energy E= hf = hc / λ
       • Where h is Planck's constant h = 6.63x10^-34 Js

4. Particle Interactions

   • 4 Fundamental Interactions
     • Gravity
       • Affects particles/objects with a mass
       • Only attractive
     • Electromagnetism
       • Affects particles with a charge
       • Attractive and Replusive
     • Strong Force/Interaction
       • Acts only on particles known as Hadrons
       • Keeps nuclei together
     • Weak Force/Interaction
       • Only mechanism which can change the flavour of quarks
       • Affects all particles
       • Causes beta decay and other interactions
   • Exchange Particles
     • Forces are caused by the exchange of photons e.g. the electromagnetic force between two charged objects is due to the exchange of virtual photons.
       • Feyman Diagrams
         • Electromagnetism
         • Electron Capture

5. Classification of Particles

   • Hadrons
     • Baryons
       • Consists of 3 quarks; all 3 are strange or none are strange
       • The proton is the only stable baryon into which other baryons eventually decay into
       • Baryon Number - Must be conserved
     • Mesons
       • Pions
         • Made up of up and down quarks (in a quark and anti-quark pair)
         • Exchange particle of the strong nuclear force
       • Kaons
         • Usually contains a strange or anti-strange quark in its pair
         • Can decay into pions
       • Consists of a quark & anti-quark pair
     • Subject to the Strong Nuclear Force
   • Leptons
     • Fundamental Particles - Cannot be broken down into anything else
     • Lepton Number - Must be Conserved
     • Lepton Number must be conserved, in the electron branch and muon branch upon muon decay
   • Strangeness
     • Always conserved/produced in strong interactions but decay/are not conserved in the weak interaction
       • Strangeness - Quantum Number

6. Quarks and Antiquarks

7. Conservation Laws

   • Charge, Baryon Number and Lepton Number must be conserved (same on both sides)
   • Charge: 0 -> +1 -1 +0
   • Baryon: 1 -> 1 + 0 + 0
   • Lepton: 0 -> 0 +1 -1

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