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Introduction to Nuclear Physics

Jul 9, 2024

Lecture Notes: Introduction to Nuclear Physics

Mass-Energy Equivalence

  • E=mc^2: Equation discovered by Albert Einstein
    • Demonstrates the relationship between mass and energy
    • Energy (E) of a particle = Mass (m) x Speed of light squared (c^2)

Nucleus of an Atom

  • Composed of protons (positively charged) and neutrons (electrically neutral)
  • Nucleons: Collective term for protons and neutrons
  • Exception: Hydrogen nucleus only has a single proton
  • Atomic number: Number of protons in a nucleus (determines the element)
  • Mass number: Number of protons + neutrons in a nucleus
    • Example: Carbon nucleus
      • 6 protons + 6 neutrons = Mass number 12
      • 6 protons + 8 neutrons = Mass number 14

Isotopes

  • Nuclei with the same atomic number but different mass numbers
  • Example: Carbon isotopes
    • Carbon-12 (C-12): 99% of carbon on Earth
    • Carbon-14 (C-14): Less stable, fewer neutrons equal more stable

Atomic Mass Units

  • Unified atomic mass unit (u): Unit for measuring the mass of nuclei
    • 1 u = 1.6605 x 10^-27 kg

Binding Energy

  • Mass of stable nucleus < Mass of individual protons + neutrons
    • Example: Helium nucleus
      • Helium atom: 4.0026 u
      • 2 protons + 2 neutrons: 4.03298 u
    • Mass difference = Binding energy
    • Binding energy: Energy needed to break apart nucleus
  • Binding energy increases with atomic number
    • Iron: Highest binding energy per nucleon
    • Very large nuclei: Lower binding energy per nucleon (less stable)

Forces in the Nucleus

  • Strong nuclear force: Holds protons and neutrons together
    • Overcomes the repulsive electric force between protons
    • Acts only over small distances
  • Larger elements require more neutrons to maintain stability

Radioactivity

  • Radioactive decay: Process of unstable nuclei breaking into stable state
  • Henri Becquerel: Discovered natural radioactivity

Types of Radioactive Decay

  1. Alpha Decay
  • Emits 2 protons + 2 neutrons (alpha particle)
    • Parent nucleus -> Daughter nucleus + Alpha particle
    • Example: Radium -> Radon + Alpha particle
    • Transmutation: Change from one element to another
    • Weakest penetrating power
  1. Beta Decay
  • Emits an electron (beta particle) and neutrino
    • Neutron turns into a proton
    • Caused by the weak force (changes quarks)
    • Intermediate penetrating power
  1. Gamma Decay
  • Emits high-energy photons (gamma rays)
    • Nucleus in excited state -> Ground state + Gamma ray
    • No transmutation
    • Strongest penetrating power

Applications and Additional Topics

  • Half-lives
  • Radiocarbon dating
  • Basics of nuclear power
  • Understanding mass-energy equivalence through practical applications

Additional Resources: Check out PBS Digital Studios for related content

Credits: Crash Course Studio and Thought Cafe team

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