Basic interactions of x-rays with matter .pptx

basic interaction of xa-ray with maters.
physics presentation

1. BASIC INTERACTIONS OF X-RAYS WITH MATTER BY MARYAM AHMAD SA’ID 12/3/22 1

2. OUTLINE INTRODUCTION DEFINITIONS BASIC ATOMIC STRUCTURE INTERACTIONS TRANSMISSION ABSORPTION SCATTER MECHANISM OF INTERACTIONS APPLICATIONS TO DIAGNOSTIC RADIOLOGY TERMINOLOGIES SUMMARY/CONCLUSION 12/3/22 2

3. Introduction X-rays are EM-waves produced from x- ray tubes by deceleration of fast moving electrons by a metal target (Tungsten) Together with gamma-rays… they are the most energetic Matter is any thing that has weight an can occupy space X-ray beam contains many of such photons at various energy levels Binding energy of an electron in an atom is the energy expended in completely removing the electron from the atom against the attractive force of the positive nucleus 12/3/22 3

4. Introduction cont…. X-ray photon vs x-ray beam source photons X-ray beam 12/3/22 4

5. Introduction cont… An atom is a particle of matter that uniquely defines an element They are bonded into molecules by electrons In their outermost shell X-ray photons may interact either with the orbital electrons or with the nucleus of atoms In the diagnostic energy range (10keV-150keV) however, interactions are always with orbital electrons 12/3/22 5

6. Introduction cont…. Basic Structure of an Atom 2n 2 n= n th shell K shell = 2 L shell = 8 M shell = 18 N , ……… 12/3/22 6

7. Basic interactions of x-rays with Matter Transmission – X-ray photon passes through unaffected Absorption – X-ray photon disappears partly or completely Scatter – X-ray photon changes direction with or without loss of energy 12/3/22 7

8. Interactions cont… Absorber Transmitted Scattered source Absorbed 12/3/22 8

9. Mechanisms involved in the processes Photoelectric Effect Compton effect Coherent Scattering Pair production Photodisintegration 12/3/22 9

10. Photoelectric Effect Interactions cont… Mechanisms 1 2 3 Positive ion 12/3/22 10 Characteristic radiation

11. Recoil Electron Scattered photon positive ion Compton Effect Interactions cont… Mechanisms 12/3/22 11

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14. Interactions cont… Mechanisms Coherent scattering 1 2 3 Scattered photon 12/3/22 14

15. Interactions cont… Mechanisms Pair production positron electron High energy photon 12/3/22 15

16. Interactions cont… Mechanisms Photodisintegration Proton Neutron Alpha particle 12/3/22 16

17. Probability of occurrence Photoelectric Effect The incident photon must have sufficient energy to overcome the binding energy of the electrons This energy must be close to & slightly above the binding energy of the electrons Involves tightly bound electrons Compton Effect Energy radiation Density of the absorber (physical & Electron) Involves free outer shell electrons 12/3/22 17

18. Probability of occurrence cont.. Coherent scattering…. low energy is involved Pair production and photodisintegration…. - High energy is required of the order 1.02MeV and 7.0MeV respectively. 12/3/22 18

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20. Applications to Diagnostic Radiology Photoelectric effect…. It produces radiographic images of excellent quality Increased patient dose. Compton Effect…. Contribute to film fog and Poses safety hazard to the personnel within the exposure area 12/3/22 20

21. Terminologies Half value layer (HVL) - thickness of a material that will reduce the intensity of a narrow beam of x-radiation to half its original value Attenuation – reduction in the number of photons of an x-ray beam Linear attenuation coefficient ( μ ) - is a parameter that quantifies the attenuating properties of a material μ = 0.693/HVL Mass attenuation coefficient – is the ratio of the linear attenuation coefficient to the density of the material μ/ ρ 12/3/22 21

22. Summary/Conclusion X- ray photons have 3 fates…. Transmitted Absorbed or Scattered Mechanisms by which they occur…. Photoelectric effect Compton effect Coherent scattering Pair production or photodisintegration Photoelectric effect and the Compton scattering are the most important in diagnostic radiology 12/3/22 22

23. THANK YOU FOR LISTENING 12/3/22 23

24. References Basic interactions between x-rays and matter. Christensen's Physics of Diagnostic Radiology 4 th edition. 4; 61-69. Interaction of x and gamma rays with matter. Farr’s physics for medical imaging. 2 nd edition. 1.4; 9-15. 12/3/22 24