Key Concepts in Artificial Transmutation and Medical LECTURE 16 Uses of Radioisotopes

Artificial Transmutation

  • High energy particles can create new nuclei by bombarding target nuclei.
  • Sources of particles can be radiation from radionuclides or accelerated charged particles.
  • Example: O-17 was created by bombarding N-14 with alpha rays; Cf-244 by bombarding U-238 with C-12.
  • Neutrons can also be used for bombardment.

Particle Accelerators

  • Linear accelerators (linacs) accelerate particles in a straight path; SLAC is the second most powerful.
  • Cyclotrons, invented by Ernest Lawrence, circularly accelerate particles.

Medical Uses of Radioisotopes

Treatment - Radiotherapy

  • Cancer treatment: radiation targeted at cancer cells, which are more sensitive than healthy cells.
  • Brachytherapy: radioisotope placed near cancer.
  • Teletherapy: external gamma radiation (e.g., Co-60) used to penetrate the body.
  • Radiopharmaceutical therapy: uses radioisotopes concentrated in specific areas.

Diagnosis

  • Radiotracers: radioisotope-tagged molecules injected to image organs.
  • Ideal tracers have short half-lives and low ionizing emissions (beta or gamma).
  • Common radiotracers include:
    • Technetium-99m (gamma, half-life 6.01 hours) - Various organs
    • Iodine-131 (beta, half-life 8.0 days) - Thyroid
    • Iron-59 (beta, half-life 44.5 days) - Blood, spleen
    • Thallium-201 (electron capture, half-life 3.05 days) - Heart
    • Fluorine-18 (positron emission, half-life 1.83 hours) - PET studies of heart, brain.

Imaging Techniques

SPECT

  • Utilizes gamma-emitting radionuclides to create images.
  • A gamma-camera detects radiation, forming 2D and 3D images via rotating cameras and reconstruction techniques.

PET (Positron Emission Tomography)

  • Involves positron-emitting radionuclides annihilating electrons, generating gamma rays.
  • PET imaging detects these gamma rays (511 KeV).
  • Systems include multiple gamma-detector rings; detection of coincidences helps map radioactivity areas.

Background Radiation

  • 50% from natural sources: radon (37%), cosmic (5%), soil (3%), internal (5%).
  • 50% from artificial sources: nuclear medicine (12%), medical procedures (36%).