In-Depth Notes on Radiopharmaceuticals and Radioactivity

Radioactivity and Radioactive Substances

  • Definition: Radioactive substances emit rays that affect photographic plates and discharge electrified bodies.
  • Characteristics:
    • Unstable elements undergo spontaneous decomposition, emitting radiation.
    • Spontaneous emission is termed Radioactivity.
    • Forty known radioactive elements categorized into the Uranium, Thorium, and Actinium series.
    • Radiation emission is independent of temperature, pressure, or catalysts.

Types of Radiation

  • Alpha Rays (α-Rays):

    • Properties:
    • Least penetrating; stopped by 1-2 cm air or a sheet of paper.
    • Positively charged particles similar to Helium nuclei, with a mass of 4 amu.
    • Ionization Power: Produces about 30,000 ion pairs/cm in air.
    • Decay:
    • Reduces atomic number by 2 and mass number by 4.
    • Only emitted by elements with atomic numbers greater than 82.

  • Beta Rays (β-Rays):

    • Types: Positrons (positive) and negatrons (negative).
    • Properties:
    • Greater penetrating power than α-rays; can pass through aluminum foil.
    • Negligible mass (~1/1836 of a hydrogen ion).
    • Decay: Changes atomic number (increases by 1 or decreases by 1) but does not alter mass number.

  • Gamma Rays (γ-Rays):

    • Properties:
    • More penetrating than α and β rays; similar to short electromagnetic waves (X-rays).
    • Unaffected by magnetic fields, possess no mass or charge.
    • Poor ionizing power, causing energy level changes without elemental changes.

Radioactive Decay

  • Definition: The process where unstable nuclei emit radiation to reach stability.
  • Types of Decay:
    • Alpha decay: Emission of α-particles.
    • Beta decay: Emission of β-particles, converting neutrons to protons or vice versa.
    • Gamma decay: Emission of excess energy as γ-rays.
  • Half-Life (t1/2): Time it takes for half of a radioactive sample to decay; varies significantly between isotopes.

Measurement of Radioactivity

  • Detection Devices:
    • Ionization Chamber: Measures radiation through ion pairs created in gas.
    • Proportional Counter: More sensitive; measures with a gas mixture.
    • Geiger-Müller Counter: Detects particles and radiation via avalanche ionization.
    • Scintillation Counter: Uses scintillator materials that emit light when struck by radiation.

Applications of Radioisotopes

  • In Therapeutics:
    • Target malignant tissues; examples include Gold-198 for effusions and Sodium Iodide-131 for thyroid treatment.
  • In Diagnosis:
    • Used as tracers in various diagnostic procedures: e.g. Ferric citrate for hematological disorders.
  • In Research:
    • Used for biological studies; Carbon-14 and Tritium for metabolic tracing.
  • For Sterilization:
    • Radiation sterilizes pharmaceuticals without heat or chemicals, effective for thermolabile substances.

Isotopes and Their Properties

  • Isotopes: Atoms of the same element with different mass numbers; contain the same number of protons but different neutrons.
  • Example Isotopes of Hydrogen:
    • Protium (H-1), Deuterium (H-2), Tritium (H-3).
  • Uranium Decay Series: A sequence of decays leading from Uranium-238 to stable Lead-206.

Safety and Handling of Radioactive Materials

  • Precautions:
    • Use protective gear; avoid direct contact.
    • Store in labeled containers, preferably in remote corners with lead shielding.
    • Regular monitoring of areas storing radioactive materials is critical to ensure safety.