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.

Radiations

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

• A 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