# INTERACTION OF PHOTONS.pptx

17 de Apr de 2022
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### INTERACTION OF PHOTONS.pptx

• 1. INTERACTION OF PHOTONS By- Dr. Aakriti Bhardwaj Moderator- Dr. Umesh V
• 2. INTRODUCTION • Absorption of energy from radiation in biological material may lead to excitation or ionization • IONIZING RADIATION : Radiation with sufficient energy to eject ≥1 orbital electrons from atom or molecules • NON-IONIZING RADIATION: Radiation that doesn’t carry enough energy to ionize atoms or molecules
• 3. Types of Ionizing Radiations • Electromagnetic • Particulate
• 4. Electromagnetic radiation • Electromagnetic waves have both electric and magnetic components. They are at right angles to each other, vary with time. • The wave moves forward with velocity ‘c’, which in vacuum = 3 x 10^10 cm/s. The distance between successive peaks of wave ‘λ‘, is wavelength. The number of waves passing a fixed point per second is frequency ‘v’. • c= λv
• 6. X-RAYS • Produced extranuclearly • Waves of electrical and magnetic energy in fields perpendicular to each other. • Streams of photons of packets of energy. • Potency of X-rays depends on the size of each individual packets ; not on the total energy absorbed.
• 7. Properties of photons • A photon is a “packet” of electromagnetic energy. • It has no mass, no charge, and travels in a straight line at the speed of light. • Photons interact differently in matter than charged particles because photons have no electrical charge. • In contrast to charged particles, photons do not continuously lose energy when they travel through matter.
• 8. • When photons interact, they transfer energy to charged particles (usually electrons) and the charged particles give up their energy via secondary interactions (mostly ionization). • The interaction of photons with matter is probabilistic, while the interaction of charged particles is certain.
• 9. Particulate radiation • This constitutes of electrons, protons, alpha particles, neutrons, negative π-mesons, and heavy charged ions. • Electrons are small, negatively charged particles that can be accelerated to high energy to a speed close to that of light by means of an electrical device, such as a betatron or linear accelerator. They are widely used for cancer therapy.
• 10. • Protons are positively charged particles and are relatively massive, having a mass almost 2,000 times greater than that of an electron. Because of their mass, they require more complex and more expensive equipment, such as a cyclotron, to accelerate them to useful energies, but they are increasingly used for cancer treatment in specialized centers.
• 11. Absorption of X-RAY • Coherent Scatter • Photoelectric Effect • Compton Effect • Pair Production • Photo Disintegration
• 13. Photoelectric process
• 14. Compton Process
• 15. Pair Production
• 16. • Radioactive tracer injected into body gets trapped within tissue of interest. • Tracer emits positrons which interact with neighbouring electrons. • Two annihilation photons are produced which is measured by PET.
• 17. • Positron emitting used are : 18-F ,11-C,13-N,15-O ; can be incorporated into a biological substrate without altering their biological activity • Provides molecular imaging of a biological function in stead of anatomy • The detection of both annihilation photons in coincidence increase the sensitivity of PET.However images are much blurier compared to CT/MRI
• 18. PHOTO DISINTEGRATION
• 19. • At energies above 8-16 MeV • Emission of neutron – more late toxicity • Not a major contributor to therapeutics • Main source of neutron contamination
• 21. Direct and Indirect action of Radiation
• 22. Indirect action of Radiation • H2O → H2O+ + e− • H2O+ + H2O → H3O+ + OH∙
• 23. • Incident x-ray photon • ↓ • Fast electron (e−) • ↓ • Ion radical • ↓ • Free radical • ↓ • Chemical changes from the breakage of bonds ↓ Biologic effects
• 24. Summary • Types of radiation-ionizing and non-ionizing • Types of ionizing radiation-electromagnetic and particulate • Absorption of X-rays: coherent scatter, photoelectric effect, compton effect, pair production, photo disintegration • Direct and indirect effect of radiation
• 25. Reference • Radiobiology for the Radiologist by Eric J.Hall, Amato J.Giaccia • Goodwin PN, Quimby EH, Morgan RH. Physical Foundations of Radiology. 4th ed. New York, NY: Harper & Row; 1970. • Johns HE, Cunningham JR. The Physics of Radiology. Springfield, IL: Charles C Thomas; 1969. • Rossi HH. Neutron and heavy particle dosimetry. In: Reed GW, ed. Radiation Dosimetry: Proceedings of the International School of Physics. New York, NY: Academic Press; 1964:98–107. • Smith VP, ed. Radiation Particle Therapy. Philadelphia, PA: American College of Radiology; 1976.
• 26. THANK YOU