8 Nuclear and Particle physics

• Why a beam of protons could be more effective treatment for tumours than a beam of X rays

  • Proton beam deposits more energy in the tumour than X rays
  • Proton beam results in less energy absorbed by surrounding tissue compared to X rays
• Why a cosmic ray could lead to the creation of a lamda particle

  • Energy of cosmic ray could be turned into mass
  • According to E=mc^2
• Explain why the Λ0 particle cannot be directly observed but information about it can be obtained by studying its decay particles

  • Neutral particles do not leave a track
  • Conservation of laws to deduce the properties of particles
  • Tracks of decay particles can be determine momentum of lamda particle
• Describe the process in which electrons are produced by the filament. Electron gun

  • Thermionic Emission
  • Electrons in heated metal to gain enough energy to be emitted from the surface
• Annihilation

  Particle and antiparticle collide the pair annihilate and the mass is converted 2 gamma photons that travel in opposite direction.
• Pair production

  Photon collides with a nucleus and energy produced creates a particle antiparticle pair

  Neutron is need for pair production to occur
• Fixed target

  • collision of fast moving particles with a stationary particle
  • P(momentum) before is the same as P(momentum) after
  • Particle creates some kinetic energy
  • Not all energy is converted to mass
• Colliding beams

  • If mass and velocity is the same the total initial momementum = 0
  • There fore p after = 0 as well
  • All kinetic energy is converted to mass based on equation

  2m = 2E/c^2
• Momentum of a photon

  
• Linacs used for radiotherapy operate by means of a standing wave formed within the linac. Explain how standing waves are produced

  • Waves travelling in opposite direction meet and superpose
  • At points where waves in phase constructive interference occurs
  • Antinodes/maximum amplitude at points where constructive interference occurs
• In Lawrence’s cyclotron, an alternating potential difference was used to accelerate particles to high energies.

  Explain the significance of the expression obtained by Lawrence to the operation of a cyclotron.

  • Time independent of speed
  • Particles spend the same time in each dees
  • So a fixed frequency can be used for the p.d
  • because the field across the gap will be in the correct direction to increases speed of the particles as they cross each time
• Explain why high energy particles are required to investigate the structure of nucleons.

  • High energy so particles have high momentum
  • High momentum so wavelength is small p=h/λ
  • Studying nucleons requires the wavelengths of the order of nucleon size
• Explain the process that enables a particle detector to detect charged particles.

  Particle is ionising

  A track is formed by the ionised particles produced
• Structure of Baryon and Meson

  Baryon is three quarks

  Meson is an anti-quark and a quark
• • There is a change in magnetic flux linkage
  • The greater the rate of change of magnetic flux linkage the larger the induced EMF
  • After the south pole reaches the coil, the flux linkage decreases
  • As south pole of the magnet passes through the coil, the induced emf is negative
  • Downward speed of magnet increases
  • EMF is zero as magnet totally leaves the coil
• 0.99c, Muon lifetime = 2.2µs

  • Relativistic speed as it is close to c / speed of light
  • Experience time dilation
  • So increase in muon life time and mass
• State three observations and the corresponding conclusions made from the alpha particle scattering experiment (6)

  • Most alpha particles were undeviated/ passed through with little or no deviation
  • Most of the atom is empty space
  • Few alpha particles were scattered by small angles
  • There is a concentration of charge in the atom
  • Very few particles were deviated by 90 degrees
  • Most of the mass is concentrated in nucleus
• Muons

  • Travel close to speed of light
  • Unstable fundamental perticle
  • Same charge as electron but greater mass
  • A high speed muon lifetime is long and mass is large compared to a stationary muon
• Discuss the extet to which the results of the alpha particle scattering experiments justified replacing the plumodel with nuclear model (rutherford)

  • Most alpha particles passed through the gold foil
  • Some were deflected by small angles
  • Very little were deflected by more than 90 degrees
  • Both models would predict little deflections because in nuclear model the atom is mostly empty space and pudding model matter is too spread out
  • Nuclear model required high concentration of charge to provide a large force
  • Pudding model didn't work as the delfection requires a high concentration of mass
• Explain why thickness of the gold foil is very small

  • Alpha cannot pass through thick foil
  • due to its ionising power
  • it won’t penetrate through
• K-

  Anti up and strange
• Quark structure of pion

  up and anti up

  down and anti down

  up and anti down

  down and anti up
• Mesons do not have a baryon number
• Baryon

  consists of 3 quarks

  Proton = p = 1 baryon number

  neutron = n = 1 baryon number

  pion = 0 baryon number ( it is a meson)
• Leptons

  Electrons and neutrinos

  fundamental particles

  eg. muon or muon neutrino

  tau

  Electron = 1 lepton number

  Electron neutrino = -1 lepton number

  
  

  Neutrinos have no charge
• Quark structure of proton

  up up down
• Quark structure of neutron

  up down down
• Explain why the protons and anti-protons needed high energies to produce the Z boson (large mass particle).

  • Mass energy is conserved according to E = mc^2
  • Needs large amounts of energy to create a high mass particle
  • Additional energy is from kinetic energy of colliding particles
• Explain why alpha particles are more suitable for these experiments compared to beta particles or gamma particles

  Alpha particles have double the charge of beta

  Alpha particles are more massive than beta

  Gamma has no charge
• Mass of proton 939Mev/c^2 Mass of pion 139Mev/c^2

  Explain why the sum of the masses of the two particles after the decay is not equal to the mass of the delta particles

  939+139 = 1078

  mass of delta = 1232 > 1078

  total mass of decay of products < mass of delta particle
• Explain how the momentum of proton compares with momentum of the pion

  Radius of proton is larger compared to pion

  due to p = Bqr

  Momentum of photon is larger than pion