Revision:OCR A Level Physics - Nuclear And Particle Physics

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Nuclear And Particle Physics

• Neutron-induced fission:
  • The splitting of a nucleus into parts caused by absorption/capture of a neutron
  • The reaction cannot start without neutrons
• Thermal neutrons:
  • Neutrons having KE comparable with KE of thermal molecular KE
  • Slow moving, low energy
  • So-called because the energies are due simply to their temperature (KE does not really contribute to their energies)
• Accelerating charged particles:
  • Use two oppositely charged electrodes with p.d. between them
  • OR use electric field
  • F = ma
• Fast moving charged particle made to follow circular path:
  • Particle moves inside magnetic field
  • Field is uniform
  • Force perpendicular to direction of motion and acts as centripetal force
  • Force causes acceleration
• Nuclear decay:
  • Means loss of alpha/beta particles from nucleus, plus gamma radiation
  • Spontaneous
• Nuclear fission:
  • Means splitting of nucleus into two (roughly equal) nuclei
  • Neutron-induced
• Coulomb barrier:
  • Electrostatic repulsion between nuclei
• Binding energy
  • The loss in mass/energy when nucleons cluster together to form an atomic nucleus
  • The energy that needs to be supplied to separate the nucleons
  • Can be though of as the energy that binds them together
• Hadrons:
  • Particles made up from quarks
  • Are affected by the strong force
  • Two types: baryons and mesons
• Leptons:
  • Fundamental particles not affected by the strong force
  • E.g. electrons
• Baryons:
  • Hadrons comprising three quarks
  • E.g. protons and neutrons
• Mesons:
  • Hadrons that consist of a quark and an anti-quark
• Nuclide:
  • Atomic nucleus with a particular number of protons and neutrons
  • Isotopes have same number of protons but different neutrons and so are different nuclides

Useful figures and formulae

• 1 u = 931.5 MeV

• 1 eV = 1.6 x10^-19 J

Plasma

• Definition:
  • Electrons have separated from nuclei
  • So plasma consists of free electrons and positive ions / is completely ionised
• Confinement:
  • Magnetic field: ions rotate around or follow magnetic field, so cannot escape
  • Strong gravitational field: nucleons and electrons pushed together by pressure of material
  • Inertial: laser beams directed inwards/converging and compress a fuel pellet

JET fusion reactor

• Reaction:

• Conditions:
  • High temperature (of gases), over 10⁶K
  • This energy is high enough for the nuclei to overcome the Coulomb barrier
  • Gas becomes very dense plasma; electrons stripped from nuclei
  • Plasma confined by magnetic field/’bottle’
• Achieving above conditions:
  • Materials contained in toroidal Tokamak
  • Ohmic heating (large current) causes heating
  • Plasma forms one-turn transformer secondary coil, leading to a low turns ratio and therefore a large current
  • Heating also caused by neutral beam injection, radio frequency, and self-heating by alpha particles
• Generating energy (note JET does not do this itself):
  • or,
  • 
  • Lithium ‘blanket’ surrounds reactor vessel
  • The KE of neutrons is transferred to lithium, causing heating
  • Coolant is circulated through the lithium
  • This heats water and converts it to steam, which drives turbines and turns electrical generators, generating useful electrical energy

Comments

• Suitable for: A Level Physics, OCR board.
• Written by: MichaelJWilliams.
• From this post.