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Revision:OCR A Level Physics - Nuclear And Particle Physics

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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Physics > OCR A Level Physics - Nuclear And Particle Physics

Contents

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
  • \displaystyle E_K = \frac{3kT}{2}
  • \displaystyle F = \frac{mv^2}{r}
  • \displaystyle F = B q v
  • \displaystyle T = \frac{2\pi r}{v}


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:

\displaystyle \mathsf{{}^2_1H} + \mathsf{{}^3_1H} \longrightarrow \mathsf{{}^4_2He} + \mathsf{10n}\ (+ \mathsf{energy})


\displaystyle \mathsf{Deuterium} + \mathsf{Tritium} \longrightarrow \mathsf{Helium} + \mathsf{neutron}\ (+ \mathsf{energy})


  • 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):
    • \displaystyle \mathsf{{}^1_0n} + \mathsf{{}^6_3Li} \longrightarrow \mathsf{{}^3_1H} + \mathsf{{}^4_2He} or,
    • \displaystyle \mathsf{{}_1^0n} + \mathsf{{}^7_3Li} \longrightarrow \mathsf{{}^3_1H} + \mathsf{{}^4_2He} + \mathsf{{}^1_0n}
    • 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


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