⚛️Intro to Applied Nuclear Physics Unit 1 – Atomic Structure and Nuclear Models

Key Concepts and Terminology

• Atom smallest unit of matter that retains the properties of an element
• Nucleus dense, positively charged core of an atom contains protons and neutrons
• Electron negatively charged particle that orbits the nucleus in shells or orbitals
• Proton positively charged subatomic particle found in the nucleus has a mass of approximately 1 atomic mass unit (amu)
• Neutron electrically neutral subatomic particle found in the nucleus has a mass slightly greater than a proton
• Isotope atoms of the same element with different numbers of neutrons
  • Isotopes have the same atomic number but different mass numbers
  • Examples include carbon-12, carbon-13, and carbon-14
• Mass number (A) total number of protons and neutrons in an atom's nucleus
• Atomic number (Z) number of protons in an atom's nucleus determines the element

Historical Development of Atomic Models

• Dalton's atomic theory (early 19th century) proposed that atoms were indivisible and indestructible
• Cathode ray experiments (late 19th century) led to the discovery of electrons by J.J. Thomson
• Thomson's "plum pudding" model depicted electrons embedded in a positively charged "pudding"
• Rutherford's gold foil experiment (1909) revealed the existence of a small, dense, positively charged nucleus
  • Most of an atom's mass is concentrated in the nucleus
  • Electrons orbit the nucleus at relatively large distances
• Bohr's atomic model (1913) introduced the concept of stationary electron orbits and energy levels
  • Electrons can transition between energy levels by absorbing or emitting specific amounts of energy
• Quantum mechanical model (1920s) described electrons as probability waves occupying orbitals
  • Schrödinger's wave equation and Heisenberg's uncertainty principle form the basis of this model

Structure of the Atom

• Atoms consist of a positively charged nucleus surrounded by negatively charged electrons
• Nucleus contains protons and neutrons held together by the strong nuclear force
  • Protons have a positive charge equal in magnitude to the electron's negative charge
  • Neutrons have no electrical charge and contribute to the mass of the nucleus
• Electrons occupy discrete energy levels or shells around the nucleus
  • Energy levels are labeled with principal quantum numbers (n = 1, 2, 3, etc.)
  • Electrons in higher energy levels are farther from the nucleus and have more energy
• Electron configuration describes the arrangement of electrons in an atom's orbitals
  • Electrons fill orbitals in order of increasing energy (1s, 2s, 2p, 3s, etc.)
  • Pauli exclusion principle states that no two electrons in an atom can have the same set of quantum numbers

Subatomic Particles and Their Properties

• Protons positively charged particles with a mass of approximately 1.67 × 10^-27 kg
  • Proton charge is equal in magnitude but opposite in sign to the electron charge
  • Number of protons in an atom's nucleus determines the element
• Neutrons electrically neutral particles with a slightly greater mass than protons (1.67 × 10^-27 kg)
  • Neutrons contribute to the mass of the nucleus and provide stability
  • Isotopes of an element have the same number of protons but different numbers of neutrons
• Electrons negatively charged particles with a mass of approximately 9.11 × 10^-31 kg
  • Electrons occupy orbitals around the nucleus and participate in chemical bonding
  • Electron configuration determines an atom's chemical properties
• Quarks fundamental particles that make up protons and neutrons
  • Protons consist of two up quarks and one down quark (uud)
  • Neutrons consist of one up quark and two down quarks (udd)

Nuclear Models and Theories

• Liquid drop model treats the nucleus as a drop of incompressible nuclear fluid
  • Explains nuclear fission and the stability of certain nuclei
  • Accounts for the spherical shape of most nuclei and the existence of nuclear surface tension
• Shell model describes nucleons (protons and neutrons) occupying discrete energy levels in the nucleus
  • Nucleons fill nuclear shells in a manner analogous to electron shells
  • Explains the enhanced stability of nuclei with certain "magic numbers" of protons or neutrons
• Collective model combines aspects of the liquid drop and shell models
  • Describes the nucleus as a combination of individual nucleon motion and collective behavior
  • Accounts for nuclear deformations and rotational and vibrational excitations
• Fermi gas model treats nucleons as a gas of non-interacting particles obeying the Pauli exclusion principle
  • Provides a simple description of nuclear properties, such as nuclear density and binding energy
  • Useful for understanding the behavior of nuclei at high temperatures or excitation energies

Isotopes and Nuclear Stability

• Isotopes are atoms of the same element with different numbers of neutrons
  • Isotopes have the same atomic number (Z) but different mass numbers (A)
  • Examples include hydrogen-1 (protium), hydrogen-2 (deuterium), and hydrogen-3 (tritium)
• Nuclear stability depends on the ratio of protons to neutrons in the nucleus
  • Most stable nuclei have a proton-to-neutron ratio close to 1 for light elements
  • Heavier elements require more neutrons than protons for stability due to the strong nuclear force
• Radioactive decay occurs when an unstable nucleus releases energy in the form of particles or electromagnetic radiation
  • Alpha decay involves the emission of an alpha particle (two protons and two neutrons)
  • Beta decay involves the emission of a beta particle (electron or positron) and a neutrino
  • Gamma decay involves the emission of high-energy photons (gamma rays)
• Half-life is the time required for half of a given quantity of a radioactive isotope to decay
  • Half-lives can range from fractions of a second to billions of years
  • Used to determine the age of materials in radiometric dating techniques

Applications in Nuclear Physics

• Nuclear power generation relies on controlled nuclear fission reactions to produce heat and generate electricity
  • Fission reactors split heavy nuclei (such as uranium-235) into lighter fragments, releasing energy
  • Challenges include safety, waste management, and nuclear proliferation concerns
• Nuclear fusion reactions power the Sun and other stars
  • Fusion combines light nuclei (such as hydrogen) into heavier elements, releasing large amounts of energy
  • Fusion research aims to develop controlled fusion reactors for clean, abundant energy production
• Medical applications of nuclear physics include diagnostic imaging and radiation therapy
  • Positron emission tomography (PET) uses radioactive tracers to visualize metabolic processes
  • Radiation therapy uses targeted ionizing radiation to destroy cancer cells
• Nuclear weapons rely on uncontrolled fission or fusion reactions to release massive amounts of destructive energy
  • Fission weapons (atomic bombs) use the rapid fission of heavy elements like uranium or plutonium
  • Fusion weapons (hydrogen bombs) use a fission reaction to trigger a more powerful fusion reaction

Challenges and Future Directions

• Nuclear waste management remains a significant challenge for the nuclear power industry
  • Radioactive waste must be safely stored and isolated from the environment for long periods
  • Research focuses on developing advanced storage methods and reducing waste generation
• Nuclear safety and security are critical concerns in the operation of nuclear facilities
  • Accidents (such as Chernobyl and Fukushima) highlight the need for robust safety measures
  • Nuclear material must be safeguarded to prevent theft or diversion for weapons purposes
• Fusion energy research aims to overcome technical challenges in achieving sustained, controlled fusion reactions
  • Magnetic confinement (tokamaks) and inertial confinement (laser fusion) are leading approaches
  • Challenges include maintaining plasma stability, achieving high temperatures and densities, and managing neutron damage to materials
• Advanced nuclear reactor designs seek to improve safety, efficiency, and sustainability
  • Small modular reactors (SMRs) offer scalability and reduced capital costs
  • Generation IV reactor concepts (such as molten salt reactors) aim to enhance safety and fuel utilization
• Fundamental research in nuclear physics continues to explore the nature of matter and the universe
  • Particle accelerators probe the structure and interactions of subatomic particles
  • Astrophysical observations and theories investigate the role of nuclear processes in stars and the evolution of the universe