Nuclear Chemistry Lecture Notes

Overview of Nuclear Chemistry

• Often overlooked in chemistry due to lack of observable changes in chemical properties.
• Focuses on nuclear processes which allow transformation of elements (e.g., changing lead into gold).
• Has significant energy implications, much greater than those in chemical reactions.

Historical Context

• Early studies by scientists like Henri Becquerel and Marie Curie focused on radioactivity.
• Radioactivity: Phenomenon where unstable nuclei emit particles, leading to development of photographic plates.

Types of Nuclear Reactions

1. Spontaneous Decay (Radioactive Decay)
   • Unstable nuclei spontaneously release high-energy particles.
2. Nuclear Bombardment (Transmutation)
   • Purposeful manipulation of nuclei by bombarding them with high-energy particles.

Nuclear Reactions Representation

• Nucleus represented as:
  • X: Element Symbol
  • A: Mass Number (protons + neutrons)
  • Z: Atomic Number (number of protons)
• Example:
  • For a decay reaction:
    • Before: X_A^Z
    • After: Y_B + emitted particle

Types of Emitted Particles

• Alpha Particles (α): Helium nuclei (2 protons + 2 neutrons) - positively charged.
• Beta Particles (β): High-energy electrons emitted when a neutron decays into a proton.
• Gamma Particles (γ): High-energy electromagnetic radiation, no mass or charge.

Penetrating Power of Radiation

• Alpha Radiation:
  • Low penetration; stopped by paper or skin.
• Beta Radiation:
  • Moderate penetration; can pass through paper, but stopped by metal.
• Gamma Radiation:
  • Highly penetrating; requires thick lead or concrete for shielding.

Radioactive Decay Processes

Alpha Decay

• Loss of an alpha particle leads to a decrease in mass and atomic numbers.
• Example: Uranium-238 → Thorium-234 + Helium-4

Beta Decay

• A neutron converts into a proton, emitting a beta particle.
• Mass number remains the same; atomic number increases by one.
• Example: Carbon-14 → Nitrogen-14 + Electron.

Positron Emission and Electron Capture

• Positron Emission: Proton converts to a neutron, emitting a positron.
• Electron Capture: Electron combines with a proton to form a neutron.

Band of Stability

• Graph showing stable nuclei based on neutron-to-proton ratios.
• Lighter elements need a 1:1 ratio; heavier elements require more neutrons than protons.

Nuclear Binding Energy

• Mass defect observed when comparing the mass of nucleons to the mass of a nucleus.
• Energy released during nuclear reactions can be calculated using Einstein's equation: E = mc².

Applications of Nuclear Chemistry

• Medical Uses: Radiotherapy, radioactive tracers for imaging (e.g., thyroid gland imaging).
• Energy Production:
  • Nuclear Fission: Uranium-235 as fuel in reactors.
  • Nuclear Fusion: Occurs in the sun; challenges in harnessing it on Earth.
• Agricultural Uses: Food irradiation to kill bacteria.

Radiation Measurement Units

• Becquerel (Bq): Activity of 1 disintegration per second.
• Curie (Ci): 3.7 x 10^10 disintegrations per second.
• Gray (Gy): Absorption of 1 Joule per kilogram of tissue.
• Rad: 0.01 Gray.
• Rem: Effective dose considering biological effectiveness.

Biological Effects of Radiation

• Ionizing radiation can damage biological tissues, potentially leading to cancer.
• Signs of radiation exposure vary based on dose:
  • 0-25 Rem: No effect.
  • 25-50 Rem: Temporary decrease in white blood cells.
  • 100-200 Rem: Nausea, significant drop in white blood cells.
  • 500 Rem: Potentially lethal (50% mortality rate in 30 days).

Conclusion

• The study of nuclear chemistry includes understanding nuclear reactions, their applications, and their impacts on health and safety.
• Nuclear fission and fusion hold potential for energy production, while safety protocols must address the risks of radiation exposure.