Lecture Notes: Nuclear Physics and Reactions

Structure of the Nucleus

• Components: Neutrons and protons held by strong nuclear force.
• Mass and Energy: Mass can convert to energy (E=MC^2).
  • During nucleus formation, some mass converts to energy (photons).
• Different Nuclei: Mass loss per proton/neutron varies by nucleus type.
• Graph: Mass loss trends
  • Light to heavy nuclei: Initial increase, then decrease beyond iron.
• Fusion vs. Fission
  • Lighter elements: Fusion releases energy.
  • Heavier elements: Fusion consumes energy.

Nuclear Fusion

• Conditions for Fusion: High pressure and temperature (e.g., stars).
• Energy Source in Stars: Fusion of lighter elements.
• Supernova: Fusion of heavier elements at star's death.
• Hydrogen Bombs: Fusion process in thermonuclear weapons.
  • Primary Explosion: Compression of hydrogen.
  • Secondary Explosion: Nuclear fusion (hydrogen to helium).

Nuclear Fission

• Mechanism: Nucleus splits, releasing energy.
• Controlled Reaction: Used in nuclear power plants with control rods.
• Uncontrolled Reaction: Used in nuclear weapons.
• Neutron Absorption: Key for starting fission chain reactions.

Energy States and Gamma Rays

• Excited Energy States: Similar for nuclei and electrons.
• Photon Emission: When nucleus drops to lower energy level.
  • Photons from nuclei are gamma rays (high energy).
• Gamma Ray Interactions
  • Pass through, absorbed by electron, energy transfer, or electron-positron pair creation.

Neutron Interactions

• Speed and Absorption: Slower neutrons more likely absorbed.
  • Most rapid slowdown when colliding with hydrogen nuclei.
• Thermal Vibrations: Neutrons match surrounding atomic energy levels.

Nuclear Stability and Decay

• Unstable Nuclei: Too many/too few neutrons for protons.
  • Various decay methods: cluster emission, neutron to proton transformation, etc.
• Decay Products: New nucleus (stable/unstable), may emit gamma rays.

Key Points

• Energy Conversion: Mass to energy in nuclear reactions.
• Fusion: Energy release in stars and bombs.
• Fission: Energy release in reactors and bombs.
• Decay: Process and products, gamma ray emission.

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