Physics and Chemistry of Radiation Absorption

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Physics and Chemistry of Radiation Absorption

  1. 1. Physics and Chemistry of Radiation Absorption Chapter 1
  2. 2. In the beginning…
  3. 3. Radiation is Everywhere
  4. 4. The Humble Discovery Wilhelm Conrad Roentgen Gas discharge tube X-rays 1895
  5. 5. Ionizing Radiation – Alpha (), beta () – Gamma (), X-ray – Protons, neutrons • Ionizing vs. Excitation Ionization Excitation
  6. 6. Ionizing Radiation • Particulate Radiation – Alpha, beta, protons, neutrons, heavy charged ions, etc. • Electromagnetic Radiation – (UV), X-rays and Gamma rays
  7. 7. X-ray/γ-ray Absorption • Photoelectric effect – Low energy range • Electron emitted • X-ray emitted • Compton Scattering – High energy range • Electron emitted • Scattered photon
  8. 8. Direct vs Indirect Action • Particulate radiation = HIGH LET – Direct Action – Damages DNA directly by breaking bonds • Electromagnetic radiation = LOW LET – Indirect Action (~two thirds of time) – Damages DNA indirectly via radicals and reactive molecules
  9. 9. Direct vs Indirect Action
  10. 10. Direct Action Cannot be modified by sensitizers or protectors
  11. 11. Indirect Action H2O H2O + e- H + H2O2 OH o HO2 OH - Ho H2 WATERIncoming Radiation Production of free radicals within the cell can result in indirect effects Most abundant molecule within humans: Water Can be modified by sensitizers or protectors
  12. 12. Indirect Action Summary Incident X-ray Photon Fast Electron (e-) Ion Radical Free Radical Chemical Changes for Breakage of Bonds Biological Effects
  13. 13. Ionizing Radiation Natural Background 82% Man-made 18% Radiation Exposure Nuclear Medicine 21% Consumer Products 16% Occupational 2% Fallout 2% Nuclear Fuel Cycle 1% Medical X- rays 58% Man-made Radiation
  14. 14. Q & A’s • 1. What is the difference between X-rays and gamma rays? a. X-rays are produced extra-nuclearly whereas gamma rays are produced in nuclear decays. b. X-rays have higher energies than gamma rays. c. X-rays and gamma rays interact with matter differently. d. A and B are correct.
  15. 15. Q & A’s • 2. What is the main source of natural background radiation? a. Electrons. b. X-rays. c. Neutrons. d. Alpha-particles. e. Gamma rays
  16. 16. Q & A’s • 3. Which photon processes are dominant in the context of diagnostic radiology? a. Compton scattering and photoelectric effect. b. Photoelectric effect and pair production. c. Compton scattering and excitation. d. Photoelectric effect and ionization.
  17. 17. Q & A’s • 4. Direct action of radiation is the dominant process for a. X-rays. b. Neutrons and alpha particles. c. Electrons. d. Gamma rays.
  18. 18. Q & A’s • 5. Which of the following statements is true? a. Indirect action can be modified by protectors or sensitizers. b. Direct action can be modified by protectors or sensitizers.
  19. 19. Q & A’s • 6. A free radical is: a. Any charged particle. b. An atom or molecule with an unpaired electron in the outer shell. c. An atom with an even number of electrons. d. A chemically stable atom.
  20. 20. Q & A’s • 7. All types of radiation can induce biologic effects by direct or indirect action. a. True. b. False.
  21. 21. Q & A’s • 8. What is the main reason for the difference in biologic effects caused by neutrons and photons? a. The energy of the radiation. b. The fact that the charged particles produced by neutrons are, for the most part, positively charged. c. The density of ionization. d. The fact that neutrons can interact with nuclei.
  22. 22. Q & A’s • 9. What is the correct order from low to high LET? a. Protons, neutrons, alpha particles, x-rays b. Alpha particles, protons, beta, gamma rays c. X-rays, beta, protons, neutrons d. gamma rays, beta, protons, alpha particles
  23. 23. Q & A’s • 10. What year did Röntgen discovery x-rays? a. 1885 b. 1886 c. 1895 d. 1897 e. I don’t care.

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