Course Material 9 Nuclear Physics

Course Outline

1. Nuclear Physics

   • a. Atomic Structure and Radioactivity

   • b. Nuclear Reactions

   • c. Applications in Medical Imaging and Treatments

Atomic Structure and Nuclear Physics

• In 1896, Henri Becquerel discovered radioactivity through exposed photographic plates from uranium.

• The atomic nucleus comprises neutrons (neutral particles) and protons (positively charged), playing a critical role in atomic stability.

Key Concepts of the Atomic Nucleus

• Neutrons act as a 'nuclear cement' helping to hold the nucleus together.

• The mass of nucleons is approximately 2000 times that of electrons, with the atom's mass closely aligned with its nucleus's mass.

• Strong Force: Responsible for binding protons and neutrons within the nucleus.

  • Strong over short distances; ineffective at larger separations.

  • Essential for the stability of nuclei, especially in heavier elements.

Radioactive Decay

• All elements heavier than bismuth (atomic number 83) are radioactive.

• Types of Radiation:

  • Alpha Particles: Positive charge, consists of 2 protons and 2 neutrons.

  • Beta Particles: Negatively charged electrons emitted from neutron transformation.

  • Gamma Rays: High-energy electromagnetic radiation with no mass.

• Decay Processes:

  • Alpha decay reduces atomic number by 2.

  • Beta decay increases atomic number by 1 without changing mass number.

Radioactive Half-Life

• Definition: Time it takes for half of a radioactive sample to decay.

  • Example: Radium-226 has a half-life of 1620 years.

  • Half-life is constant and unaffected by external factors.

• Carbon-14 dating uses its 5730-year half-life to date organic materials.

Applications of Nuclear Physics

Medical Imaging

• Radiopharmaceuticals used in PET (Positron Emission Tomography) and SPECT imaging.

• Gamma camera: Utilizes scintillators to detect gamma rays and produce images.

Radiotherapy

• Treatment of tumors using targeted gamma radiation (example: Cobalt-60).

Nuclear Reactions

• Nuclear Fission: Splitting of atomic nuclei releasing more energy than radioactivity.

  • Initiated by neutron absorption, resulting in a chain reaction.

  • Requires specific conditions and isotopes (U-235 for fission reactions).

Controlling Nuclear Fusion

• High temperatures are needed to overcome repulsion between positively charged nuclei.

• Potentially unlimited energy from fusion, particularly using hydrogen isotopes (deuterium and tritium).

Safety and Risks

• Radiation Exposure: Variably sourced, with natural background radiation accounting for the majority.

• Health Concerns: Cell repair mechanisms can handle low-level exposures, but prolonged or high exposure increases cancer risk.

  • Awareness of the types of radiation (alpha, beta, gamma) is essential for safety.