1 / 25

Understanding X-ray Interactions in Matter

Explore the intricate interactions between X-rays and matter through coherent scattering, Compton scattering, and the photoelectric effect. Learn how different tissues absorb radiation and the role of secondary electrons. Discover the significance of beam attenuation and radiation dose measurements.

agreenleaf
Télécharger la présentation

Understanding X-ray Interactions in Matter

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. INTERACTION OF X RAYS WITH MATTER

  2. INTERACTION BETWEEN X-RAYS AND MATTER Coherent Scattering Photoelectric effect Compton Scattering

  3. COHERENT SCATTERING 8 % Classic scattering Incident X-ray photon Scattered X-ray photon Low energy photons only scattering, no Ionization and only little energy loss

  4. COHERENT SCATTERING – Rayleigh (coherent) scatter interaction with entire atom . Photon changes direction (though usually by small angle) . “Elastic” scattering: Photon energy unchanged . Most important for “soft” (low energy) . and x rays (< 10 keV) . Adds very little to film fog

  5. COMPTON SCATTERING Compton effect or Compton scattering (C) incoherent scattering: Directly proportional to electron density Can occur with very low atomic weight targets even at relatively low X-ray energies 62 %

  6. COMPTON SCATTERING • An x-ray photon of lower energy is scattered from the • atom • Proportional to electron density of absorber • Interaction with outer electron • Changes direction • Adds to film fog 62 %

  7. COMPTON SCATTERING • Incident X-ray changes direction and loses energy, imparting that energy to the electron (Compton electron) • Compton electron interacts with other atoms producing secondary ionizations • Possess relatively low energy, produce low energy x- rays • Energies of 100 keV -- 10 MeV – absorption of radiation mainly due to the Compton effect

  8. PHOTOELECTRIC EFFECT Interaction with bound atomic electron . Incident photon disappears . Photon energy absorbed by electron . Momentum absorbed by atom . Probability of PE absorption increases for: » Low incident photon energy » High electron density in medium (mass density x Z) . Following absorption, photoelectrons, and “characteristic” x rays are emitted

  9. PHOTOELECTRIC EFFECT 30 % • Critical indiagnostic X rays • Ionization occurs • Binding energy is small for biologic tissues • Usually with - K shell electron • Recoil electron travels only short distance

  10. DIFFERENTIAL ABSORPTION Different tissues - different amount of absorption Makes radiographs possible Hard tissue - mostly absorbed Soft tissue - heterogeneous beam Mainly by photoelectric effect - varies with third power of Z Of absorber 6.5 times more in bone than water

  11. SECONDARY ELECTRONS • Electrons ejected by photoelectric effect or • Compton effect • Energy given up by: • Collisional ionization or excitation • Radiative Bremsstrahlung radiation low energy

  12. BEAM ATTENUATION Reduction in intensity while passing through mattter Either by photo electric effect or Compton scattering Half Value Layer - thickness of an absorber needed to reduce the number of x ray photon by half

  13. RADIATION DOSE The International System (SI) unit • Radioactivity • Exposure • Absorbed Dose • Dose Equivalent • Effective dose

  14. RADIATION DOSE Activity: rate at which the isotope decays. Radioactivity may be thought of as the volume of radiation produced in a given amount of time. International System (SI) unit - Becquerel (Bq) (curie (Ci) Exposure: measure of the strength of a radiation field at some point in air. measure made by a survey meter.  Gray Gy (Roentgen (R) Effective dose: Sum of product of equivqlent dose to each organ or tissue Sivert Si

  15. RADIATION DOSE Absorbed Dose:amount of energy that ionizing radiation imparts to a given mass of matter. SI unit gray (Gy), “rad” (Radiation Absorbed Dose)   1 rad - 0.01 Gy  Different materials that receive the same exposure may absorb different energy  Dose Equivalent:  relates the absorbed dose to the biological effect of that dose absorbed dose of specific radiation X "quality factor" = dose equivalent (SI unit - sievert (SV), (rem)" One rem = 0.01 SV  X- or Gamma radiation - the quality factor is 1

  16. Radiation quantities and units

  17. DOSIMETRY Quantity of radiation exposure Radiation dosimeters are devices which are capable of measuring an accumulated absorbed dose of ionizing radiation • issued four times a year • - rate measuring instruments and    - personal dose measuring instruments • Direct • Indirect. 

  18. DOSIMETERS Film Badges Ring Dosimeters

  19. DOSIMETERS Pocket Dosimeter - Direct Read Pocket Dosimeter Digital Electronic Dosimeter Ionization Counters Scintillation Counters Particle Track Devices The Cloud Chamber Geiger Muller Counter

  20. THERMOLUMINESCENT DOSIMETERS (TLDS) 15% for low doses 3% for high doses TLD - a phosphor, such as lithium fluoride (LiF) or calcium fluoride (CaF), in a solid crystal structure exposed to ionizing radiationradiation interaction ionization trapping of free electrons Heating the crystal Release of energy as light 1 millirem

  21. Thermoluminescence dosimeter T L material T L D reader EXPOSURE Equipment used to measure T L heated Emitted light proportonal to absorbed dose

  22. Parts of TLD reader • HEATER • PHOTOMULTIPLIER TUBE • HEAT FILTER ALOW THE LIGHT TO PASS • MEASURE THE EMMITED LIGHT • ELECTRONIC SYSTEM • (POWER SUPPLY)

  23. AVAILABILITY • TLD AVAILABLE IN • SOLID • POWDER • APPLICATION OF TLD • RADIOTHERAPY • RADIODIAGNOSIS • PERSONAL MONITORING

  24. P M TUBE FILTER TLD READER PROCEDURE TRAY HEATER

More Related