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COHERENT SCATTE-WPS Office.pptx
- 1. BASIC INTERACTION B/WX-RAYS AND MATTER
- 2. • X-rays arephotons(EM rays without mass)& they interact with orbital electrons of an atom • 5 ways by which the X-rays photons interact: • 1)COHERANT SCATTERING • 2)PHOTO-ELECTRIC EFFECT • 3)COMPTON SCATTERING • 4)PAIR PRODUCTION • 5)PHOTODISINTEGRATION
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- 4. • Also calledas Classical and Unmodified scattering • Happens when incoming xray photon has energy less than the binding energy of orbital electron • Interaction in which radiation undergo change in direction without change in wavelength
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- 6. THOMAS SCATTERING A singleelectron is involved in interaction
- 7. RAYLEIGH SCATTERING Xray photoninteract with all electrons in an atom
- 8. • Only typeof interaction b/w Xray & matter that doesn't cause ionisation(no energy exchange) • Only effect is to change the direction of the incident radiation • Only less than 5% incident radiation
- 9. PHOTO-ELECTRIC EFFECT Photoelectric effectcan occur when an incident photon has energy little more than the binding energy of electron in an atom
- 11. Photon with energymore than binding energy Photon disappears
- 12. Energy of photon Overcomebinding energy Kinetic energy of released e- Photo-electric effect Photo electron Characteristic radiation Positive ion
- 13. Probability of occurrence •The incident photon must have sufficient energy to overcome the binding energy of the electron. • A photoelectric reaction is most likely to occur when the photon energy and electron binding energy are nearly the same, provided of course that the photon's energy is greater
- 14. • Tighter anelectron is bound in its orbit,the more likely it is to be involved in a photoelectric reaction
- 15. Application of Characteristic radiation Produceradiographic image of excellent quality Patient recieve more radiation than from any other interactions
- 16. Image quality No scatterradiation production It enhances natural tissue contrast
- 17. Radiation exposure To decreasethe radiation exposure due to photoelectric effect we use radiation with high kvp High Kvp High penetration power Low absoption
- 18. COMPTON SCATTERING • Interactionb/w high energy photon and outer shell electron with negligible binding energy. • Electron is ejected from atom and photon is scattered with some reduction in energy • Scatter Xray emerging from this interaction is called compton scatter and ejected electron is called recoil electron
- 20. Energy of incident photon Goesto recoil electron as its kinetic energy Retained by deflected photon
- 21. Energy retained in scatterdphoton Initial energy of incident photon Angle of deflection of photon
- 22. • Change inwavelength of scattered photon is:
- 23. • Conversion ofwavelength to energy of photon
- 24. • Lower theangle of deviation, higher is the energy retained by scattered radiation • Photons scattered at narrow angles will reach xray film and will create a fog. • Cannot be removed by filters(high energy )& cannot be removed by grid(narrow angle of deviation) • Since scatter radiation maintain same energy it also cause radiation hazard.
- 25. Probability of occurrence •Depends on • 1)Total no of e- in an absorber(density of absorber) • 2)Energy of the radiation(as the energy of the photon increases the no of reactions decreases)
- 26. Pair production Photon interactwith nucleus of atom Photon disappeares Energy converted to 2 particles Electron Positron (Both has same msss with energy of 0.51mev)
- 27. Pair production occurwith a photon of energy 1.02 mev only,which is not used in diagnostic radiology
- 28. Photodisruption • High energyphoton ejects a part of nucleus. • The ejected part can be a proton,neutron or aan alpha particle • Photon energy should be greater than nuclear binding energy (7-15 mev)
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