Nuclear Chemistry

General Overview of Nuclear Chemistry

• Instructor: Dr. William Antonio Boyle
• Textbook: Moore/Stanitski, Chapter 18

The Nature of Radioactivity

• Antoine Henri Becquerel (1896):
  • Discovered U salts emitted rays that fogged photographic plates.
  • U metal was found to be a stronger emitter.
• Marie and Pierre Curie:
  • Isolated Polonium (Po) and Radium (Ra) which exhibited similar behavior.
  • Marie Curie termed the phenomenon radioactivity.
• Joseph John Thomson and Ernest Rutherford:
  • Investigated radiation and discovered two types: alpha (α) and beta (β) particles.
• Henri Becquerel's & Villard’s Contributions:
  • Villard discovered gamma (γ) radiation.

Types of Radiation

• Table of radiation types includes:
  • Alpha particle (α): Symbol = He²⁺, Charge = +2, Mass = 6.65 x 10⁻²⁴g, Penetrating power ≈ 0.03 mm
  • Beta particle (β): Symbol = e⁻, Charge = -1, Mass = 9.11 x 10⁻²⁸g, Penetrating power ≈ 2 mm
  • Gamma radiation (γ): Symbol = γ, Charge = 0, Mass = 0, Penetrating power ≈ 100 mm
  • Note: Mass ratios suggest mα ≈ 10,000 mβ

Nuclear Reactions

• Rutherford & Soddy (1902): Defined radioactivity as the transformation of a radioactive isotope into a different element via decay.
• Example:
  • Decay of Radium-226 ($^{226}<em>{88}Ra$) to Radon-222 ($^{222}</em>{86}Rn$) + α particle ($^{4}_{2}He$).

Alpha & Beta Particle Emission

• Alpha Emission:
  • $^{234}<em>{92}U ightarrow ^{230}</em>{90}Th + He$
• Beta Emission:
  • $^{90}<em>{38}Sr ightarrow ^{90}</em>{39}Y + e^{-1}$
• Mechanism behind beta decay involves:
  • Neutron ($n$) transforms into a proton ($p$) and an electron ($e^{-1}$).

Radioactive Series

• A decay product (daughter isotope) often proves unstable leading to a radioactive decay series:
  • Number of neutrons can be calculated as: $N = A - Z$, where A is the mass number and Z is the atomic number.

Other Types of Decay

• Positron Emission: A positron is a positive electron ($e^+$) which interacts destructively with matter.
  • Example: $^{43}<em>{21}Sc ightarrow ^{43}</em>{20}Ca + e^+$
• Electron Capture (EC): Occurs when an inner-shell electron is captured by the nucleus.
  • Example: $^{7}<em>{4}Be + e^{-1} ightarrow ^{7}</em>{3}Li$

Stability of Atomic Nuclei

• Stability Criteria:
  • Generally, for lighter elements, $N ext{ (neutrons)} <br /> eq Z ext{ (protons)}$.
  • Odd atomic numbers lead to less stability.
  • Heavy elements such as bismuth (Bi) have no stable isotopes.

Band of Stability & Decay Types

• Elements with Z < 83 typically decay to reach stability (e.g., via β- decay).
• Heavier isotopes (>83) primarily undergo alpha decay to achieve stability.
• Isotopes which are too light or too heavy can often decay via beta (+) emission or electron capture to balance the neutron/proton ratio.

Binding Energy

• Binding energy reflects the energy necessary to maintain nucleon cohesion within a nucleus.
  • Calculated using Einstein’s theory: $E = mc^2$.
  • Example: Determine binding energy for Carbon-12 (12C) by comparing individual nucleon masses to total nucleus mass:
  • For Carbon-12, $ext{Binding Energy } (E_b) = ext{mass of nucleons} - ext{mass of nucleus}$

Rates of Disintegration

• Radioactive decay follows first-order kinetics: $ext{ln }[X]<em>t = -kt + ext{ln }[X]</em>0$.
• Half-life: t_{1/2} = rac{0.693}{k}.
• Example: For 239Pu with a half-life of 24,400 years, the amount remaining can be calculated over several half-lives.

Applications of Radioactivity

1. Food Irradiation: Uses gamma rays to sterilize and increase shelf life without making food radioactive.
2. Medical Imaging: Radioactive tracers like 99mTc provide imaging information while minimizing biological damage.
3. Therapeutic Applications: Radiation therapy targets rapidly dividing cancer cells, exploiting their higher susceptibility to radiation than normal cells.

Nuclear Power

• Nuclear Reactors:
  • Utilize controlled fission reactions to generate energy; controlled by materials such as cadmium and boron.
  • Difference between reactor-grade and weapons-grade uranium (>90% U-235 for bombs).
• Pros & Cons:
  • Clean energy with little CO2 emission versus concerns about radioactive waste and safety.
• Future challenges include difficulties with nuclear fusion as a clean power source, requiring significant energy inputs and complex containment.

Conclusion

• Radioactivity presents vast applications across multiple fields including energy generation and medicine, though safety and waste management remain areas for ongoing concern and development.