Physics Radioactivity in Medicine

Overview of Micro Cameras

  • Micro cameras integrated into mobile phones.

  • Setup rotates around the patient's phone, capturing images quickly.

  • Patient's body is also introduced into the machine.

  • Highlighting modern engineering accomplishments.

Introduction to Ionizing Radiation

  • Today's topic involves two lectures focusing on ionizing radiation.

  • The first lecture centers on radioactivity, leading to discussions on ionizing radiation.

  • Upcoming presentation intended to be engaging and informative.

Nucleus and Atomic Structure

Composition of the Nucleus

  • The nucleus consists of protons and neutrons.

  • Protons: positively charged particles.

  • Neutrons: neutral particles (no charge).

  • Electrons orbit around the nucleus, balancing the atom's charge.

Mass Concentration and Size

  • More than 99% of an atom's mass is in the nucleus.

  • Atoms are mostly empty space with nuclei significantly smaller than the overall atom size.

Nucleons

  • Protons and neutrons collectively referred to as nucleons.

  • Neutrons are approximately 0.1% heavier than protons.

  • Electronic mass (9.1 × 10^-31 kg) is significantly smaller than that of protons and neutrons.

Mass Number and Isotopes

Understanding Atomic and Mass Numbers

  • Mass number (A) = number of protons (Z) + number of neutrons (N).

  • Example: Uranium (U), atomic number 92, mass number 238, equals 146 neutrons.

  • Stable elements typically maintain an equal number of protons and neutrons.

Isotope Concept

  • Isotopes: Atoms of the same element with different neutron counts.

  • Hydrogen isotopes include:

    • Hydrogen-1 (protium)

    • Hydrogen-2 (deuterium)

    • Hydrogen-3 (tritium)

Nuclear Forces

Electromagnetic Forces and Strong Nuclear Force

  • Protons repel each other due to like charges.

  • Strong nuclear force (SNF) overcomes this repulsion at very short ranges (10^-15 meters).

  • SNF is critical in maintaining nucleus stability among nucleons.

Forces at Play in the Nucleus

  1. Gravity: Long-range force, less effect at small scales.

  2. Electromagnetic Force: Familiar, governs charge interactions.

  3. Strong Nuclear Force: Short-range, binds nucleons together.

  4. Weak Nuclear Force: Governs radioactive decay processes.

Stability and Radioactivity

Stability in Smaller Nuclei

  • Small nuclei (few protons) are generally stable, equal protons/neutrons balance.

  • Beyond atomic number 83, stability is rare; more neutrons required for large nuclei stability.

Nuclear Disintegration and Radioactivity

  • Nuclear disintegration or radioactivity occurs when nuclei are unstable.

  • Spontaneous disintegration leads to three major types of decay:

    • Alpha decay

    • Beta decay

    • Gamma decay

Types of Radioactive Decay

Alpha Decay

  • Emission of an alpha particle (helium nucleus).

  • Example: Uranium-238 decays to Thorium-234.

  • Each alpha decay transmits a helium nucleus and a decrease in the mass and atomic number of the parent nucleus.

Beta Decay

  • Involves the transformation of protons and neutrons:

    • Beta Negative Decay: Neutron converts to a proton, emitting an electron (beta particle).

    • Beta Positive Decay: Proton converts to a neutron, emitting a positron.

  • Example of Beta Negative: Carbon-14 decays to Nitrogen-14.

Gamma Decay

  • Nucleus releases excess energy as gamma rays without changing nucleon composition.

  • No transmutation occurs; element remains the same but at a lower energy state.

Binding Energy

Concept of Binding Energy in the Nucleus

  • Binding energy refers to the energy that holds nucleons together in the nucleus.

  • A portion of mass from nucleons is converted to energy during nucleon formation.

  • Example calculation shows that helium has binding energy of about 28.3 MeV due to mass deficit (difference in mass before and after nucleon formation).

Average Binding Energy Trends

  • Plotted against mass number; binding energy peaks around iron, indicating high stability.

  • Fusion occurs below iron as energy can be released; fission occurs for heavier elements post-iron due to stability.

Cosmic and Stellar Fusion

  • Elemental fusion in stars leads to heavier elements, impacting stellar life cycles.

  • Fusion processes in stars create lighter elements until iron, after which stability fails, leading to collapse and explosions that contribute to cosmic nucleosynthesis.

  • All elements originate from stars, contributing to Earth's radioactivity.

Conclusion

  • Understanding radioactivity and the forces within the nucleus is crucial for grasping nuclear processes and their applications in science and technology.