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Basic interactions of x-rays with matter .pptx
- 1. 09/28/2024 1 BASIC INTERACTIONSOF X-RAYS WITH MATTER BY MARYAM AHMAD SA’ID
- 2. 09/28/2024 2 OUTLINE • INTRODUCTION –DEFINITIONS – BASIC ATOMIC STRUCTURE • INTERACTIONS – TRANSMISSION – ABSORPTION – SCATTER • MECHANISM OF INTERACTIONS • APPLICATIONS TO DIAGNOSTIC RADIOLOGY • TERMINOLOGIES • SUMMARY/CONCLUSION
- 3. 09/28/2024 3 Introduction • X-raysare 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
- 4. 09/28/2024 4 Introduction cont…. X-rayphoton vs x-ray beam source photons X-ray beam
- 5. 09/28/2024 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
- 6. 09/28/2024 6 Introduction cont…. BasicStructure of an Atom 2n2 n= nth shell K shell = 2 L shell = 8 M shell = 18 N , ………
- 7. 09/28/2024 7 Basic interactionsof 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
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- 9. 09/28/2024 9 Mechanisms involvedin the processes • Photoelectric Effect • Compton effect • Coherent Scattering • Pair production • Photodisintegration
- 10. 09/28/2024 10 Photoelectric Effect Interactionscont… Mechanisms 1 2 3 Positive ion Characteristic radiation
- 11. 09/28/2024 11 Recoil Electron Scatteredphoton positive ion Compton Effect Interactions cont… Mechanisms
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- 14. 09/28/2024 14 Interactions cont… Mechanisms Coherentscattering 1 2 3 Scattered photon
- 15. 09/28/2024 15 Interactions cont… Mechanisms Pairproduction positron electron High energy photon
- 16. 09/28/2024 16 Interactions cont… Mechanisms PhotodisintegrationProton Neutron Alpha particle
- 17. 09/28/2024 17 Probability ofoccurrence 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
- 18. 09/28/2024 18 Probability ofoccurrence cont.. • Coherent scattering…. – low energy is involved • Pair production and photodisintegration…. - High energy is required of the order 1.02MeV and 7.0MeV respectively.
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- 20. 09/28/2024 20 Applications toDiagnostic 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
- 21. 09/28/2024 21 Terminologies • Halfvalue 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
- 22. 09/28/2024 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
- 23. 09/28/2024 23 THANK YOUFOR LISTENING
- 24. 09/28/2024 24 References • Basicinteractions between x-rays and matter. Christensen's Physics of Diagnostic Radiology 4th edition. 4; 61-69. • Interaction of x and gamma rays with matter. Farr’s physics for medical imaging. 2nd edition. 1.4; 9-15.