Notes on Nuclear Physics Lecture

Introduction to E=mc²

• E=mc²: Mass-energy equivalence discovered by Albert Einstein.
• Indicates mass can be converted to energy and vice versa.
• Fundamental in the study of nuclear physics.

The Nucleus

• Composed of protons (positively charged) and neutrons (neutral).
• Except for hydrogen, all elements have both protons and neutrons (collectively called nucleons).

Atomic and Mass Numbers

• Atomic Number: Number of protons in a nucleus (determines the element).
• Mass Number: Total number of protons and neutrons.
  • Example:
    • Carbon with 6 protons and 6 neutrons: Atomic Number = 6, Mass Number = 12.
    • Carbon with 6 protons and 8 neutrons: Atomic Number = 6, Mass Number = 14.

Nuclear Notation

• Chemical symbol for an element with atomic number and mass number:
  • Carbon-12: [ ^{12}_{6}C ]
  • Carbon-14: [ ^{14}_{6}C ]
• Isotopes: Nuclei with the same atomic number but different mass numbers.
  • Example: Most Carbon on Earth is Carbon-12, while Carbon-14 is less common.

Mass and Binding Energy

• Total mass of a stable nucleus < total mass of individual protons and neutrons.
  • Example: Helium atom (4.002603 u) vs. its component parts (4.032980 u).
• The difference in mass is binding energy: energy to break the nucleus apart.
• Binding energy per nucleon decreases for larger nuclei beyond iron.

The Strong Nuclear Force

• Strong Nuclear Force: Attracts nucleons, overcoming repulsive forces between protons.
• Acts over short distances; larger nuclei need extra neutrons for stability.
• Chart shows neutron-to-proton ratios for stability.

Radioactivity

• Radioactivity: Decay of unstable nuclei into stable forms, releasing energetic particles.
  • Henri Becquerel: Discovered natural radioactivity.

Types of Radioactive Decay

1. Alpha Decay:

   • Nucleus loses 2 protons and 2 neutrons (alpha particle).
   • Example: Radium decays into Radon.
   • Low penetrating power (stopped by paper).

2. Beta Decay:

   • Emits a beta particle (electron) and a neutrino.
   • Neutron turns into a proton, causing transmutation.
   • Medium penetrating power (stopped by aluminum).

3. Gamma Decay:

   • Emission of gamma rays from excited nuclei to lower energy state.
   • No transmutation occurs.
   • High penetrating power (requires concrete/lead for blockage).

Conclusion

• Key concepts covered:
  • Atomic number, mass number, nuclear notation.
  • Binding energy and mass-energy equivalence.
  • Strong and weak nuclear forces.
  • Three types of radioactive decay: alpha, beta, gamma.
• Understanding of E=mc² and its implications in nuclear physics.