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Nuclear Physics

Geiger-Marsden α-scattering
  • Experiment: A beam of α-particles is fired at a thin gold foil
  • Results of the experiment:
    • Most particles pass straight through
    • Some are scattered appreciably
    • Very few — 1 in 8,000 — suffered deflections > 90°
  • Conclusion:
    • All mass and charge are concentrated in the center of the atom. Therefore, the nucleus is very small and very dense
    • The nucleus is positively charged as α-particles are repelled/deflected
The Nuclear Atom
  • Nucleon number is the total number of protons and neutrons
  • Proton/atomic number: is the total number of protons
  • Isotopes are atoms of the same element with a different number of neutrons but the same number of protons
Nuclear Processes
  • During a nuclear process, nucleon number, proton number, and mass-energy are conserved
  • Radioactive processes are random and spontaneous
    • Random: Impossible to predict and each nucleus has the same probability of decaying per unit time
    • Spontaneous: Not affected by external factors such as the presence of other nuclei, temperature and pressure
  • Evidence on a graph:
    • Random: The graph will have fluctuations in count rate
    • Spontaneous: The graph has the same shape even at different temperatures, pressures, etc.

Types of Decays
  • α-decay: Loses a helium proton
  • β-decay: Neutron turns into a proton and an electron and electron antineutrino are emitted
  • β+-decay: Proton turns into a neutron and a positron and electron neutrino are emitted
  • γ-decay: A nucleus changes from a higher energy state to a lower energy state through the emission of electromagnetic radiation (photons)
Fundamental Particles
  • Fundamental Particle is a particle that cannot be split up into anything smaller
  • Electron is a fundamental particle but protons and neutrons are not
  • Protons and neutrons are made up of different combinations of smaller particles called quarks
  • Table of Quarks
  • Quark Models:
  • All particles have their corresponding antiparticle
  • A particle and its antiparticle are essentially the same except for their change
  • Table of Antiquarks
  • These antiquarks combine to similarly form respective antiprotons and antineutrons
Quark Nature of β-decay
  • Conventional model of β-decay:
    • β-decay: n → p + β + v̄
    • β+-decay: p → n + β+ + v
  • Quark model of β-decay:
    • β-decay:
    • β+-decay:
  • Quarks undergo change to another quark in what is called a ‘weak interaction’
Particle Families

  • There are other families under Leptons
  • Leptons are a part of elementary particles

  • There are other families under Hadrons too
  • Hadrons are a part of composite particles