Physics - Particle Physics

• Atomic structure

  • Small nucleus contains protons and neutrons
  • Electrons orbiting nucleus
• What is an atom?

  The entire individual particle that contains subatomic particles.
• What is the nucleus?

  The central part of an atom that contains protons and neutrons. Where the mass is located.
• What is a nucleon?

  A specific nucleus
• What are nuclei?

  Group of nucleons
• How can radioactive isotopes be used to calculate age of opbjects?

  • All living beings contain the same ratio of carbon-14 to carbon-12. The radioactive isotope carbon-14 is absorbed from the atmosphere
  • After they die, the carbon-14 inside decays
  • Scientists can use the percentage of Carbon-14 left and compare it with isotopic data to calculate the age
• How do you work out the specific charge of something?

  charge/mass
• What are the 3 forces in the nucleus?

  Gravitational force

  Electrostatic repulsion

  Strong Nuclear Force
• What is the approximate size of the gravitational force in the nucleus?

  It is small because the particles are small.
• The electrostatic force in the nucleus is much larger than gravitational force, trying to hold them together. Therefore the nucleus should fall apart. It doesnt because of the Strong Nuclear Force.
• Strong Nuclear force

  • Strong
  • Acts between all nucleons
  • Has no effect beyond 3 *10^15m (3fm)
  • Attractive 0.5fm - 3fm
  • Repulsive <0.5fm
• What happens during Alpha decay?

  Emission of an Helium nucleus. 4 Neutrons and 2 Protons.
• Beta minus - Too many Neutrons, Neutron decays into a proton, electron and anti neutrino.

  Beta plus - Too many protons, proton tuens into neutron, positron and neutrino
• Gamma radiation - Nuclide has excess energy so gives off gamma radiation. No change to nucleon number
• What is a photon?

  Packet of electromagnetic energy.
• Photon energy E=hf
• h = plancs constant
• 1eV = 1.602x10^-19 J
• E = hc/λ
• Pair production is when a photon with enough energy will turn into a particle and its corresponding antiparticle. Minimum energy of photon needed = 2 x Rest energy of the partcles created. Any kinetic energy the particle have after is additional energy.
• E=mc^2 shows that energy can be converted to mass and vice versa.
• Annihalation is when a particle and its corresponding antiparticle make 2 photons that go in opposite directions to conserve momentum. The energy of the photons released = 2hf
• When two particles interact with eachother they exert forces on one another. These can be repulsive or attractive. Exchange particles called bosons cause these forces. Bosons are an example of an exchange particle.
• Exchange particles exist for a short amount of time and transfer energy and momentum. This is theoretical.
• Electromagnetic force

  • Two particles repel eachother due to this force
  • Two particles could also attract eachother
  • Exchange particle is a virtual photon
• Weak Nuclear Forces

  • Causes Beta decay
  • Neutron --> Proton or Proton --> Neutron
  • Exchange particle is a W-Boson^+/-
• Look at Feynman diagrams in notebook 1. Rules:

  • Incoming particle at bottom
  • Should only be one wiggly line
  • All other lines straight and must connect
  • Wiggly line has to have a particle at each end
• Lepton type conservation

  The total electron muon or lepton numbers must be conserved in any interaction individually so leptons are split into the specific lepton groups
• View particle model in notebook 1.
• What is Baryon number?

  How many baryon particles something has - 0,1,-1
• Mesons

  • Made of 2 quarks
  • Very unstable
  • Made of quark, antiquark pair
  • E.g. Kaons, pions
• Leptons are not affected by the Strong Nuclear Force and are fundamental particles so decay into other leptons

  Lepton number

  0 - no lepton

  1 - lepton

  -1 - antilepton
• Quarks are a group of elementary subatomic particles consisting of up ,down and strange. We are given their properties in our formula book.
• Pions are not strange, kaons are strange
• A proton is UUD, A neutron is UDD
• Key facts in notebook 1.