Lecture on Atomic Structure and Nuclear Physics

Introduction

• Focus on nuclei in atomic structure; often referred to as nuclear physics.

Historical Discoveries in Atomic Structure

• JJ Thompson:
  • Discovered atoms consist of positive and negative charges.
  • Proposed the "plum pudding model" where electrons dot a positively charged substance.
• Ernest Rutherford:
  • Found the existence of a small, dense, positively charged nucleus.
  • Electrons orbit the nucleus at a distance.
• Neils Bohr:
  • Introduced the concept of electrons existing in shells or orbitals.
• James Chadwick:
  • Discovered neutrons, neutral charges in the nucleus.
  • Identified protons as the positive charges in the nucleus.

Atomic Structure and the Periodic Table

• Symbols and Numbers:
  • Bottom number: Atomic number (number of protons).
  • Top number: Mass number (protons + neutrons).
• Isotopes:
  • Atoms with the same number of protons but different numbers of neutrons.
  • Example: Carbon-13 with seven neutrons compared to Carbon-12.

Radiation

• Definition: Emission of particles or waves.
• Electromagnetic Spectrum:
  • All radiation, except gamma rays, is emitted by electrons.
  • Gamma rays emitted by nuclei with excess energy.
• Effects and Dangers
  • Gamma rays can ionize atoms, causing damage such as cancer.

Types of Nuclear Decay

• Alpha Decay:

  • Heavy nuclei emit alpha particles (2 protons, 2 neutrons).
  • Example: Americium-241 to Neptunium.
  • Alpha particles are similar to helium nuclei.

• Beta Decay:

  • Neutron transforms into a proton and emits an electron (beta particle).
  • Increases atomic number by one, mass stays the same.

Properties of Radiation

• Alpha Particles:
  • High ionizing ability.
  • Stopped by air or paper.
  • Used in smoke detectors.
• Beta Radiation:
  • Moderate ionizing ability and penetrating power.
  • Used in measuring material thickness.
• Gamma Radiation:
  • Low ionizing ability but high penetration.
  • Used in medical treatments and sterilization.

Measuring Radioactivity

• Concepts:

  • Decay rate measured in counts per second (Becquerel, BQ).
  • Half-life: Time for activity or mass to reduce by half.

• Calculations:

  • Example problem-solving for half-life.

Nuclear Processes

• Fission:

  • Splitting of large nuclei (e.g. Uranium-235).
  • Releases energy and additional neutrons, potentially causing chain reactions.

• Fusion:

  • Light nuclei (e.g. hydrogen) fuse to form heavier nuclei (e.g. helium).
  • Occurs in the sun, releases more energy, requires high kinetic energy.

Challenges in Nuclear Fusion

• Difficulty in harnessing energy in a controlled, sustainable way.

Conclusion

• Continuation of scientific research in nuclear physics is crucial for understanding and harnessing nuclear processes.